Synthesis and Characterization of Single-Phase Metal Dodecaboride Solid Solutions: Zr1- xYxB12 and Zr1- xUxB12

Article abstract of DOI:10.1021/jacs.9b03482

Single-phase metal dodecaboride solid solutions, Zr_0.5Y_0.5B₁₂ and Zr_0.5U_0.5B₁₂, were prepared by arc melting from pure elements. The phase purity and composition were established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), and ¹⁰B and ¹¹B solid-state nuclear magnetic resonance (NMR) spectroscopy. The effects of carbon addition to Zr_1-xY_xB₁₂ were studied and it was found that carbon causes fast cooling and as a result rapid nucleation of grains, as well as "templating" and patterning effects of the surface morphology. The hardness of the Zr_0.5Y_0.5B₁₂ phase is 47.6 ± 1.7 GPa at 0.49 N load, which is ～17% higher than that of its parent compounds, ZrB₁₂ and YB₁₂, with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr_0.5U_0.5B₁₂ is ～54% higher than that of its UB₁₂ parent. The dodecaborides were confirmed to be metallic by band structure calculations, diffuse reflectance UV-vis, and solid-state NMR spectroscopies. The nature of the dodecaboride colors - violet for ZrB₁₂ and blue for YB₁₂ - can be attributed to charge-transfer. XPS indicates that the metals are in the following oxidation states: Y³⁺, Zr⁴⁺, and U^5+/6+. The superconducting transition temperatures (T_c) of the dodecaborides were determined to be 4.5 and 6.0 K for YB₁₂ and ZrB₁₂, respectively, as shown by resistivity and superconducting quantum interference device (SQUID) measurements. The T_c of the Zr_0.5Y_0.5B₁₂ solid solution was suppressed to 2.5 K.

Full text of DOI:10.1021/jacs.9b03482

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Article
Synthesis and Characterization of Single Phase
1-x
x
12
1-x
x
12
Metal Dodecaboride Solid Solutions: ZrYB and ZrUB
Georgiy Akopov, Wai H. Mak, Dimitrios Koumoulis, Hang Yin, Bryan Owens-
Baird, Michael T. Yeung, Mit H. Muni, Shannon Lee, Inwhan Roh, Zachary C.
Sobell, Paula L. Diaconescu, Reza Mohammadi, Kiril Kovnir, and Richard B. Kaner
J. Am. Chem. Soc., Just Accepted Manuscript • Publication Date (Web): 07 May 2019
Downloaded from http://pubs.acs.org on May 7, 2019
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Synthesis and Characterization of Single Phase Metal Dodecaboride Solid Solutions: Zr1-
xYxB12 and Zr1-xUxB12
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Georgiy Akopov1,2,3, Wai H. Mak1, Dimitrios Koumoulis1, Hang Yin1, Bryan Owens-Baird2,3,
Michael T. Yeung4, Mit H. Muni1, Shannon Lee2,3, Inwhan Roh1,5, Zachary C. Sobell1,7, Paula L.
Diaconescu1, Reza Mohammadi7*, Kirill Kovnir2,3* and Richard B. Kaner1,8,9*
1Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los
Angeles, CA 90095, USA
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2Department of Chemistry, Iowa State University, Ames, IA 50011, USA
3Ames Laboratory, U.S. Department of Energy, Ames, IA 50011, USA
4Department of Chemistry, Northwestern University, Evanston, IL 60208, USA
5College of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
6Department of Chemistry and Biochemistry, University of Colorado Boulder, Boulder, CO 80309
7Department of Mechanical and Nuclear Engineering, Virginia Commonwealth
University, Richmond, VA 23284, USA
8Department of Materials Science and Engineering, University of California, Los Angeles (UCLA),
Los Angeles, CA 90095, USA
9California NanoSystems Institute (CNSI), University of California, Los Angeles (UCLA), Los
Angeles, CA 90095, USA
* Corresponding authors: rmohammadi@vcu.edu, kovnir@iasate.edu, kaner@chem.ucla.edu
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ABSTRACT
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Single-phase metal dodecaboride (MB12) solid solutions, Zr0.5Y0.5B12 and Zr0.5U0.5B12 were
prepared by arc melting from the pure elements. The phase purity and composition were
established by powder X-ray diffraction (PXRD), energy-dispersive X-ray spectroscopy (EDS),
X-ray photoelectron spectroscopy (XPS) and 10B and 11B solid-state nuclear magnetic resonance
(NMR) spectroscopy. The effects of carbon addition to Zr1-xYxB12 were studied and it was found
that carbon causes fast cooling and as a result rapid nucleation of grains, as well as “templating”
and patterning effects of the surface morphology. The hardness of the Zr0.5Y0.5B12 phase is 47.6 ±
1.7 GPa at 0.49 N load, which is ~17% higher than that of its parent compounds, ZrB12 and YB12,
with hardness values of 41.6 ± 2.6 and 37.5 ± 4.3 GPa, respectively. The hardness of Zr0.5U0.5B12
is ~54% higher than that of its UB12 parent. The dodecaborides were confirmed to be metallic by
band structure calculations, diffuse reflectance UV-vis and NMR spectroscopies. The nature of the
dodecaboride colors – violet for ZrB12 and blue for YB12 – can be attributed to charge-transfer.
XPS indicates that the metals are in the following oxidation states: Y+3, Zr+4 and U+5/+6. The
superconducting transition temperatures (Tc) of the dodecaborides were determined to be 4.5 and
6.0 K for YB12 and ZrB12, respectively, as shown by resistivity and SQUID (superconducting
quantum interference device) measurements. The Tc of the Zr0.5Y0.5B12 solid solution was
suppressed to 2.5 K.
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INTRODUCTION
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The compositional breadth of metal borides has resulted in a remarkable range of crystal
structures.1,2 This structural diversity yields exciting optical, magnetic and electronic,3–7
catalytic,8,9 and mechanical properties.1,10–12 Metal boride structures range from metal rich sub-
borides13 (M4B) to mono-,14,15 di-16,17 and tetraborides,18–20 to boron rich borides: dodecaborides21
(MB12) and higher borides22 (MB66), and β-rhombohedral boron doping phases23,24 (MB50-100); as
well as ternary and multinary metal borides.1,25 Of the aforementioned boride families, metal
dodecaborides are interesting due not only to having superior mechanical properties
(superhardness),26–29 but also interesting optical (color)26–28 and electronic (superconductivity)30
properties, as well as good oxidation resistance.26
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Metal dodecaborides can crystallize in two different structures: cubic-UB (
) and
퐹푚3푚
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tetragonal-ScB12 (I4/mmm) (Figure 1).1,21,26,31 The majority of metals form the cubic phase1,21 and
only Sc, as well as solid solutions based on ScB12 (at <5 at.% secondary metal addition),
crystallizes in the tetragonal structure.26,31–33 The dodecaboride structure can be thought of as a
face-centered cubic (FCC), or body-centered tetragonal (BCT) for ScB12, lattice of 12-coordinate
metal atoms, each surrounded by a 24 boron atom cuboctahedron cage. Whether a metal can form
a dodecaboride phase is primarily determined by the size of the metal in a 12 coordinate
environment; generally, the metal has to have a 12-coordinate radius in between that of zirconium
(1.603 Å) and yttrium (1.801 Å).28,34 Moreover, slight deviations from this range, as in the case of
hafnium (1.580 Å)35 and gadolinium, require high-pressure (6.5 GPa) synthesis34,35 or ambient
pressure stabilization via solid-solution formation (Y1-xHfxB12 and Zr1-xGdxB12).27–29
Most metal dodecaboride phases are incongruently melting, and as such can either be
formed as a mixture of MB12 and a lower boride (e.g. ZrB2 and YB6) or as MB12 and a higher
boride or crystalline boron (e.g. YB66 and ZrB50).36,37 This severely limits their potential
applications in tooling and as abrasives, due to having either boron-rich phases, which can form
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boride phases with the binder metals, or having the soft lower boride phases (ZrB2 and YB6), which
hinder the mechanical properties and also reduce the thermal conductivity of the material and as
such heat removal from the tool edge.38
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Metal dodecaborides can be synthesized as single crystals via zone melting, which is not
easily scalable.38 However, using solid solution alloying, here we have synthesized a single-phase
metal dodecaboride phase, Zr0.5Y0.5B12 and Zr0.5U0.5B12, as confirmed by powder XRD, scanning
electron microscopy (SEM) and solid-state NMR spectroscopic data. The fact that these alloys are
single phase not only makes it easier to study their properties, but also in the case of mechanical
properties has the added benefit of solid-solution hardening resulting in enhanced hardness, i.e.
47.6 ± 1.7 GPa at 0.49 N load – a 17% increase in hardness over that of the parent phases (ZrB12
and YB12). Furthermore, we have studied the effects of the addition of carbon to the zirconium-
yttrium dodecaboride system, as well as provide a possible explanation for the color in metal
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dodecaborides using diffuse-reflectance, XPS and solid-state NMR (10B and B) spectroscopy.
Additionally, we studied the magnetic, electronic and thermal properties of the 50/50 at.% solid
solution as well as the parent phases. We show that from one single boride structure, subtle
variations of stoichiometry can yield a wide range of outcomes, and that careful optimization of
even a few atomic percent can yield optimal properties of a superhard, superconducting boride.
For the purposes of this manuscript, boron carbide (~B12-xC2-x)39,40 will be referred to as
“B4C” and zirconium carbide (~ZrC1-x)41 as “ZrC”.
EXPERIMENTAL PROCEDURE
Pellets of the following nominal compositions: (Zr1-xYx):Cz:13B, (x = 0.00, 0.05, 0.25, 0.50,
0.70, 0.75, 0.95 and 1.00; z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0, C = B4C + ZrC; 13 boron
equivalents account for the evaporation of boron during arc-melting; the amount of pure Zr metal
was adjusted based on the concentration of ZrC, while the total amount of boron was adjusted
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based on the amount of boron in B4C), Zr:Cw:13B and Y:Cw:13B (w = 1.0, 2.0 and 3.0),
(Zr0.5Y0.5):Cz:13B (z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0 and C = B4C, ZrC + B4C and graphite),
(Zr1-xUx):20B, (x = 0.00, 0.05, 0.25, 0.50, 0.70, 0.75, 0.95 and 1.00; metal to boron ratio of 1 : 20
was used in order to conserve uranium metal), Zr:2.5B, Y:9.0B, boron carbide, (B4C):zB (z = 2.5,
6, 9, 16, 22 and 36), zirconium carbide, tungsten carbide were prepared from high-purity metal
and boron powders: amorphous boron (99+%, Strem Chemicals, USA), zirconium (99.5%, Strem
Chemicals, USA), yttrium (99.9%, Strem Chemicals, USA), depleted uranium metal wire (US
Department of Energy), boron carbide (99+%, Strem Chemicals, USA), zirconium carbide (99.5%,
Alfa Aesar, USA), tungsten carbide (99.5%, Strem Chemicals, USA) and carbon (graphite, 99+%,
Strem Chemicals, USA). In addition, cadmium sulfide (99.999+%, Strem Chemicals, USA),
titanium metal (99.9%, Strem Chemicals, USA), chromium metal (99.9%, Strem Chemicals, USA)
and potassium permanganate (98%, Alfa Aesar, USA) were used in UV-vis diffuse-reflectance
studies. Additionally, ZB12 and YB12 samples with a 1 : 20 metal to boron ratio were prepared for
SQUID magnetometry analysis. The amounts of metal were stoichiometrically based on 0.15 g of
boron in each sample.
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To ensure homogeneous mixing, the weighted powder samples were homogenized in a
vortex mixer for ~1 minute and pelletized under a load of 10 tons using a hydraulic press (Carver).
The pressed pellets were then placed in an arc-melter onto a copper hearth along with oxygen
getter materials (zirconium or titanium metal). The arc-melter chamber was later sealed and
evacuated for 20 minutes followed by purging with argon, this process was repeated 4 times to
ensure that no oxygen was present in the chamber. During arc-melting, the getters were melted
first to ensure the absorbance of any trace oxygen, and then the samples were heated for T ~ 1 to
2 minutes at I ~ 145 Amperes until molten then allowed to solidify, flipped and re-arced 2 more
times to ensure homogeneity.
The synthesized ingots were cut into 2 roughly equal pieces using a diamond saw. One half
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of the ingot was crushed for PXRD using the diamond crusher into a 325 mesh (≤45 μm) powder.
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PXRD was performed on a Bruker D8 Discover powder X-ray diffractometer (Bruker Corporation,
Germany) utilizing a CuKα X-ray beam (λave = 1.5418 Å, λKα1 = 1.5406 Å, λKα2 = 1.5444 Å, λKβ
is absorbed by a Ni filter) in the 5 - 100° 2θ range with a scan speed of 0.1055°/s, time per step of
0.3 s. The phases analyzed were cross-referenced against the Joint Committee on Powder
Diffraction Standards (JCPDS) database. Maud software was used to perform the unit cell
refinements.42–46
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The remaining half of the ingot was mounted in epoxy resin for Vickers hardness
measurements and SEM/EDS using an epoxy/hardener set (Allied High Tech Products Inc., USA),
and then polished to an optically flat finish on a semi-automated polisher (Southbay Technology
Inc., USA) using both silicon carbide abrasive disks of 120 - 1200 grit (Allied High Tech Products
Inc., USA) and 30 - 1 µm particle-size diamond films (Southbay Technology Inc., USA).
The morphology of the surfaces of the samples was analyzed using an UltraDry EDS
detector (Thermo Scientific, USA) and an FEI Nova 230 high-resolution scanning electron
microscope (FEI Company, USA). Vickers hardness testing was performed using a MicroMet
2103 Vickers microhardness tester (Buehler Ltd., USA) with a pyramidal diamond indenter tip. 15
indents were made at applied loads of 0.49, 0.98, 1.96 N each, and a minimum of 10 indents were
made at loadings of 2.94 and 4.9 N each. The indents were carried out on randomly chosen spots
of the samples. A high-resolution optical microscope (Zeiss Axiotech 100HD, Carl Zeiss Vision
GmbH, Germany) with 500× magnification was used to measure the length of the diagonals of
each indent. Vickers hardness (Hv) was calculated using Equation 1:
1854.4 퐹
Hv =
(1)
푎2
where F is the loading force applied in Newtons (N), a is the average of the length of the two
diagonals of each indent in micrometers (µm) and Hv is Vickers hardness in gigapascals (GPa).
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The reflectance spectra were collected using a diffuse-reflectance attachment on a UV-vis-
NIR spectrophotometer (Shimadzu Corp., Japan) in a 400 – 800 nm range (0.5 nm steps) using
BaSO4 powder as background. The acquired reflectance spectra was converted to pseudo-
absorbance applying Kubelka-Munk theory, using Equation 2:
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2
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%푅
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(2)
%푅
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2(
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where %R is the percent reflectance and Ap is the logarithm of the pseudo-absorbance.
XPS spectra were collected using a Kratos Axis Ultra DLD spectrometer equipped with a
monochromatic Al Kα X-ray source. Raw data processing was performed using CasaXPS 2.3
software. Spectral binding energies were calibrated by assigning the C 1s peak with a binding
energy of 284.5 eV. For high resolution XPS, samples were Ar+ sputter cleaned at an accelerating
voltage of 4 kV.
A Bruker AV III 600 (14.10 Tesla) nuclear magnetic resonance (NMR) spectrometer was
employed for the acquisition of 11B and 10B NMR signals at the frequencies of 192.57 MHz (11B)
and 64.51 MHz (10B), respectively. Specifically, the B and B NMR spectroscopic data were
acquired by using the magic-angle spinning (MAS) technique. The MAS NMR measurements
were performed with the use of a 3.2-mm outside diameter zirconia rotor.47 The NMR spectra were
obtained at several spinning rates, ranging from 5 - 17 kHz. The boron background effect resulting
from the boron nitride stator in the MAS probe was minimized by the use of the “elimination of
artifacts in NMR spectroscopy” pulse sequence.48 For the 11,10B saturation recovery measurements
with MAS at a rate of 17 kHz, the method of pulsing asynchronously to the spinning sample was
applied as initially proposed by Yesinowski, et al.49 All samples were washed in dilute
HCl/methanol in order to remove any iron content from powderizing. In addition, all samples were
mixed with a small amount of NaCl in order to reduce particle-to-particle contacts. The 11,10B
chemical shift scales were calibrated using the unified Ξ scale,50 by relating the nuclear shift to the
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1H resonance of dilute tetramethylsilane in CDCl3 at a frequency of 600.13 MHz. According to
the Ξ scale, the BF3 etherate compound is the reference for defining zero ppm. The chemical shift
referencing was further verified experimentally by acquiring the 11,10B resonance of an aqueous
solution of boric acid at pH = 4.4,51 as well as by measuring a BF3 etherate sample50 using a
solution state NMR spectrometer (Bruker AV 600). Analysis and simulations of the MAS NMR
spectra were performed by using the Solids NMR Models “sola” in the TopSpin software.
The band structures and density of states (DOS) of YB12 and ZrB12 were calculated using
the tight binding-linear muffin tin orbital-atomic sphere approximation (TB-LMTO-ASA)
program.52 The UB12 band structure was not calculated due to the presence of correlated f-electrons.
The reported crystal structures (YB12: ICSD-23860 and ZrB12: ICSD-409635) were used in the
calculations. The calculations used basis sets of Y (5s, 4d), Zr (5s, 5p, 4d), and B (2s, 2p) atomic
orbitals, with the 4f and 5p (Y), 4f (Zr), and 3d (B) atomic orbitals downfolded. The band structures
and DOS of each structure were calculated after convergence of the total energy on a dense k-mesh
of 323232 points, with 897 irreducible k points.
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Electrical resistivity was measured from 1.9 - 300 K using a Physical Property
Measurement System (Quantum Design). Arc-melted samples of YB12, ZrB12, and Zr0.5Y0.5B12
were cut and polished into regular shapes. Electrical resistivity was measured using the Alternating
Current Transport option and a four-probe geometry with 50 μm Pt wires and Ag paste.
SQUID magnetometry was performed in the 2 – 300 K range initially to narrow down the
range of the Tc and in 2 – 10 K range for other samples with a 0.5 K step size using liquid helium
on a Quantum Design Magnetic Properties Measurement System (Quantum Design, USA). The
prepared samples were split into pieces, which could fit into a capsule inserted into a plastic sample
holder. The samples were treated with HCl, washed with ethanol and weighed out before inserting
into the magnetometer. The baseline run of the sample holder was subtracted from the sample
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signal. All runs were done under an applied field of 10-3 Tesla (10 Oersted).53
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RESULTS AND DISCUSSION
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Previously, the metal dodecaborides were synthesized with a metal to boron ratio of 1 to
20, in order to prevent the formation of lower boride phases, such as ZrB2 and YB6.26–29 However,
in this study we wanted to see whether it is possible to synthesize a single-phase dodecaboride
using an almost stoichiometric amount of boron (compensated for the evaporation during arc-
melting), similar to the case of WB4, which has to be synthesized using a metal to boron ratio of
at least 1 to 8.519,54–56 in order to prevent the formation of WB2, but can be prepared as a single-
phase compound by substituting in W for ~32 at.% Ta.19 Here, we have discovered that a 50/50 at.%
solid solution of ZrB12 and YB12, prepared with a composition of (Zr0.5Y0.5):13B, is a single-phase
compound as confirmed by powder XRD (Figure 2), EDS (Figure S1) and 11B NMR spectroscopy
(Figure 10). As can be seen from the PXRD, the amount of secondary lower boride phases, ZrB2
and YB6, decreases with the increased amount of secondary metal, and they are suppressed at the
eutectic composition, which can be attributed to the formation of a solid solution. ZrB12 and YB12
are fully soluble in each other (both being cubic-UB12 structures) and form solid-solutions in the
whole range of compositions.26 This is unsurprising as Zr and Y satisfy all four requirements for
solid solution formation according to the Hume-Rothery rules:57–59 1) their atomic radii are within
~15 % of each other (rZr = 1.55 and rY = 1.80 Å);60 2) they form phases with the same crystal
structure (cubic-UB12 structure type);1 3) they have similar electronegativities (1.33 and 1.22 for
Zr and Y, respectively);61,62 and 4) they have similar oxidation states (Zr+4 and Y+3).63 The solid-
solution formation is also evident in the change of lattice parameters on going from ZrB12 (a =
7.411(6) Å) to YB12 (a = 7.502(1) Å), closely following Vegard’s law64 as well as in the EDS
values for the yttrium concentration being consistent with the nominal composition (Table 1).
Furthermore, the formation of the single-phase compound at the 50/50 at.% composition can be
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seen in the SEM image in Figure 4 as well as in the results of the NMR spectroscopy discussed
later. The ability to synthesize a single phase metal dodecaboride at stoichiometric metal to boron
ratios (accounting for boron evaporation during arc-melting) by means of a solid-solution
formation allows for a much easier synthesis of possible tools and abrasives and their superior
properties due to both solid-solution hardening (mechanical properties) and better thermal
conductivity (due to having only grains of one phase).38 The only other methods for producing
“phase pure” metal dodecaborides are: having excess boron (M : B = 1 : 20), which results in a
considerable amount of boron-rich phases; and zone (induction) melting, although producing
single crystals with exact stoichiometry is not easily scalable; furthermore single crystals have
inferior mechanical properties than their polycrystalline counterparts.26–29,38
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Upon the addition of carbon to the dodecaboride system, a change in the relative quantity
of secondary phases can be observed (Table 2, Figure 2). The change of the unit cell parameters
for the MB12 phase upon the addition of yttrium and carbon can be seen in Table 3. This is due to
the fact that while carbon does form metal borocarbides65 for low metal to boron ratios (~1 : 1), in
the case of higher borides and dodecaborides, carbon can be considered an insoluble impurity
(Figure S3) and as such will preferentially form B4C, thus reducing the total amount of available
boron in the system. However, the addition of carbon has a remarkable effect on the surface
morphology of the samples (Figures 3 and 4). Carbon has a similar effect to that of zirconium on
tungsten tetraboride,54 in that it causes a rapid cooling and as such very fast nucleation of grains,
dramatically reducing their size. This is especially dramatic upon the addition of additional
equivalents of carbon, as seen in Figure 3, where the lower borides, ZrB2, and B4C form a lamellar
microstructure pattern resulting from an eutectoid transformation of ZrB2 and B4C.66 As can be
seen from Figure 4, upon the addition of carbon, the large “white linear” ZrB2 and “spiral” YB6
phases are replaced with a large number of smaller grains. This is similar to the addition of carbide
particles to steel, where those particles go to grain boundaries during solidification/annealing and
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pin the grain boundaries. The full effect of the addition of carbon on the (Zr1-xYx):13B solid
solution can be seen in Figures 5 and 6. Note that in the case of ZrB2, a directional grain growth
can be seen, where ZrB2 and B4C grains are intermixed, which can be attributed to the high melting
points of both ZrB2 and B4C (~3230 and ~2450 °C, respectively),36,39 whereas these phases
crystallize before the main dodecaboride phase (~2000 °C)36,37 and serve as “templates”/nucleation
points for grain growth, similar to the effect of Ti on WB4.54
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In order to investigate whether a source of carbon has any effect on the resulting
phase/morphology formation, we performed a study using alloys with a nominal composition of
(Zr0.5Y0.5):Cz:13 B, where z = 0.2, 0.4, 0.5, 0.8 and 1.0, and the following sources of carbon B4C,
B4C + ZrC and graphite (Figures S10 and S12). According to the PXRD data in Figure S10, in
all three cases of different carbon sources, the phase formation is similar, accounting for slight
differences in relative intensities of the peaks. Furthermore, optical images in Figure S12 show
that phase formation is indeed independent of the carbon source. Based on these facts, it can be
inferred that in the case of ZrC as the carbon source, ZrC dissociates upon melting into zirconium
and carbon, which go on to form the metal dodecaboride and boron carbide phases, respectively;
B4C dissociates into boron and carbon and reforms back into boron carbide; and graphitic carbon
(and boron) form boron carbide. These results are important because they show that multiple
sources of carbon can be used to form the desired phases, resulting in easier synthesis, especially
at low concentrations of carbon addition due to the low molecular weight of carbon.
Figure S6 shows the PXRD of (Zr1-xUx):20B (1 : 20 metal to boron ratio was used due to
the limited amount of U metal available), which shows the formation of a solid-solution between
ZrB12 and UB12 (both being cubic-UB12 structure).1 The solid-solution formation is also evident in
the change of lattice parameters on going from ZrB12 (a = 7.411(6) Å) to UB12 (a = 7.475(1) Å),
closely following Vegard’s law64 as well as in the EDS values for the uranium concentration being
consistent with the nominal composition (Table 1). Figure S13 shows the morphology of the
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dodecaboride phases formed for these alloys, which is similar to cases of other dodecaborides
prepared at this metal to boron ratio.26–29
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Vickers hardness for alloys with a composition of (Zr1-xYx):13B, and (Zr1-xYx):C1.0:13B
can be seen in Figure 9. In both cases a hardness enhancement can be observed upon increasing
the concentration of secondary metal, culminating at the 50/50 at.% composition. In the case of
(Zr1-xYx):13B, the hardness increases from 41.6 ± 2.6 and 37.5 ± 4.3 GPa, for Zr:13B and Y:13B,
respectively, to 47.6 ± 1.7 GPa at 0.49 N load for (Zr0.5Y0.5):13B. The low hardness of the Y:13B
alloy can be attributed to the large amount of the soft YB6 phase (27.3 ± 1.2 GPa at 0.49 N load,
Figure S14). This hardness can be attributed to solid-solution hardening effects as outlined by the
Hume-Rothery rules discussed above.57–59 Furthermore, the 50/50 at.% solid solution has an
enhanced bulk-modulus of K0 = 320 ± 5 GPa (k’0 = 1.2 + 0.1), compared to the parent compounds,
Zr:13B and Y:13B, respectively, at K0 = 276 ± 7 GPa (k’0 = 2.0 + 0.4) and K0 = 238 ± 6 GPa (k’0
= 3.0 + 0.1).67 The solid solution supports the highest differential stress, due to the differences in
the radii of Zr and Y and the boron cages.67
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Upon the addition of one equivalent of carbon to (Zr1-xYx):13B, a similar hardness trend
can be observed, culminating at the 50/50 at.% composition. The hardness increases from 46.9 ±
3.7 and 37.8 ± 3.3 GPa, for Zr:C1.0:13B and Y:C1.0:13B, respectively, to 48.0 ± 3.8 GPa at 0.49 N
load for (Zr0.5Y0.5):13B. Although, with the addition of carbon, the amount of softer secondary
phases increases (27.3 ± 1.2 and 26.0 ± 2.7 GPa at 0.49 N for YB6 and ZrB2, respectively, Figure
S14), it is offset by the formation of superhard B4C (Figure S14), resulting in larger error bars
(Figure 7). A more complete picture of the Vickers hardness change for the (Zr1-xYx):Cz:13B
system, with the simultaneous variation of both metal and carbon concentrations, can be seen in
the 2D contour plots in Figure 13 (complete list of hardness and error values can be seen in Table
S1). The general trend in hardness here is that samples near the 50/50 at.% metal composition tend
to be the hardest, which can be attributed to intrinsic (solid-solution) and extrinsic (multiple phases
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(Zr1-xYxB12, ZrB2, YB6 and B4C) and grain size (Hall-Petch)68–71) hardening.
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The hardness for the system with the composition (Zr1-xUx):20B can be seen in Figure 8.
Here again solid-solution hardening can be seen for the 50/50 at.% composition, especially when
comparing it to pure UB12. The hardness increases from 41.3 ± 1.126,28,29 and 28.1 ± 5.3 GPa, for
Zr:20B and U:20B, respectively, to 43.4 ± 3.1 GPa at 0.49 N load for (Zr0.5U0.5):20B. Again, both
zirconium and uranium satisfy the Hume-Rothery57–59 rules for solid-solutions: 1) atomic size
within ~15% (1.55 and 1.75 Å for Zr and U, respectively)60, 2) ZrB12 and UB12 crystallize in the
same structure (cubic-UB12)1, 3) Zr and U have similar electronegativities (1.33 and 1.38 for Zr
and U, respectively),61,62 and 4) Zr and U have similar oxidation states (Zr4+ and U5.5+, 5.5+ being
a combination of 5+ and 6+).63
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XPS was used to analyze the oxidation state of the metal and the surface composition of
the dodecaboride system. There has been a single attempt to ascertain the oxidation state of the
metal in a dodecaboride,63 and thus this is worth revisiting. Figures S16 and S17 shows XPS
survey spectra of (Zr1-xYx):13B and (Zr1-xUx):20B systems. The B 1s peak was observed at a
binding energy of ~187 eV along with the metal peaks for Zr, Y and U depending on the sample.
These spectra also contained O 1s and C 1s peaks due to possible oxidation and surface
contaminants. Elemental composition was calculated (Table 4) for the metal and boron to compare
the varying metal ratios within a system. The atomic percent may not be an accurate representation
of the actual composition due to peak overlap of the B 1s and Zr 3d, but can be used to verify
relative ratios of the respective metals as already shown through EDS. To investigate the oxidation
state of the metals, high-resolution XPS spectra (Figures S18 and S19) were obtained. As an
example, (Zr0.50Y0.50):13B was analyzed using high-resolution scans for the Y 3d, B 1s, and Zr 3d
peaks. The samples were sputtered with Ar+ to clean off any surface contaminants prior to these
high-resolution scans. A Shirley background was used for peak fitting with spin-orbit splitting
clearly observed for Y 3d and Zr 3d. The metallic Y 3d5/2 and Y 3d3/2 components at 155.3 and
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157.4 eV was observed along with the Y3+ components observed at 157.8 and 160.1 eV for Y 3d5/2
and Y 3d3/2,72,73 respectively. The Zr 3d peak also exhibited spin-orbit splitting with the Zr 3d5/2
and Zr 3d3/2 at 180.5 and 182.5 eV, respectively, corresponding to Zr4+, and peaks at 178.8 and
181.5 eV corresponding to metallic Zr, which is similar to literature values.74,75 The high-
resolution scan was able to deconvolute B 1s from the Zr 3d peak even though the two peaks were
not well resolved in the survey scan. In the instance of (Zr0.25U0.75):20B (Figure S19), a simple
peak fitting was carried out on a high resolution XPS spectra of the U 4f peak showing spin-orbit
splitting of the U 4f7/2 and U 4f5/2 peak. Sputtering of these samples was not needed. The oxidation
state of U can be determined by observing the difference in binding energy between the satellite
and U 4f5/2 peak.76 Due to the low concentration of uranium, the satellite peaks were not easily
determined. Our XPS spectra agrees with that of UB12 which has previously been analyzed.77,78
The splitting within the main U 4f7/2 and U 4f5/2 peak signals a multivalent state for uranium. Based
on previous calculations from high temperature TGA63 of the oxidation states of uranium, +5 and
+6 are the most likely charges on uranium within our system.
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Another interesting property of metal dodecaborides is that these phases possess color
(Figures 3, 4, 5 and 7). The color changes from blue for YB12 and violet for ZrB12 to metallic for
UB12. Although exhibiting color, all dodecaborides are considered to be metals and not
semiconductors.30,79 Therefore, the existence of color can be attributed to a charge-transfer (similar
to KMnO4, Figure S21) from the boron cage to the metal; and changes with the oxidation state of
the metal: Y3+, Zr4+, and U5+/6+ (Figure S20).63 The diffuse-reflectance spectra for alloys with a
composition of (Zr1-xYx):13B (Figure S20) show a change in the maxima of pseudo-absorbance
(after Kubelka-Munk transformation)80–85 shift from 594 (ZrB12, violet) to 730 (YB12, blue) nm,
closely following Vegard’s law64 values (Table 1 and Figures 4 and S19). For the alloys with a
composition (Zr1-xUx):20B, upon the addition of 25 at.% U, the samples lose color and behave
more like metals30 (Figures S13 and S20).
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Figure 10 presents the 11B MAS NMR spectra of Zr1-xYxB12 compounds (prepared as (Zr1-
xYx):13B) at ambient temperature. The spinning rate was 17 kHz, sufficient to narrow the
lineshapes and observe the isotropic shift. Different boron environments will have different
chemical shifts and number of resonances in the NMR spectrum. The experimental (Figure 10,
left) and simulated 11B MAS (Figure 10, right) lineshapes are presented in Figure 10, where good
agreement between them can be observed. This indicates that in the case of ZrB12 and YB12
additional boron resonances (boron sites) arise at the upfield regime matching to the existence of
ZrB2 (-29 ppm) and YB6 (2.9 ppm) secondary phases, respectively. Extra boron resonances were
not detected in Zr0.5Y0.5B12, which suggests that all the boron atoms in this material have similar
chemical environments. As shown in the inset (Figure 10, left), a systematic 11B resonance shift
was detected with the increased yttrium content in the Zr1-xYxB12 series. Particularly, our data show
that the 11B isotropic resonance position for ZrB12 that lies around 10 ppm progressively shifts to
16 ppm for Zr0.5Y0.5B12 and finally reaches 25 ppm in the case of YB12. The different resonance
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position of each B NMR spectrum verifies that the Y atoms are incorporated into the crystal
lattice and, thus, affect the boron bonding environments (Figure 10, right). Moreover, the entire
Zr1-xYxB12 series is metallic and the downfield resonance shift can arise from the differences in
the atomic orbital type (s, p, d states) contributions to the density-of-states at the Fermi level from
ZrB12 to YB12. Reported86,87 and our (Figure S22) electronic structure calculations for MB12 show
that the dominant contributions to the states in the vicinity of the Fermi level are from B 2p and Y
or Zr 4d orbitals, whereas the B 2s contribution is almost negligible. The presence of d-states
amply polarizes the inner s-shells, despite the fact that the 2p hyperfine interactions are weak
compared to the s and d contributions.88,89 Hence, the observed frequency shift is also proportional
to the amount of unpaired d-states around the Fermi level due to the admixture of s-d or p-d
wavefunctions,89,90 as seen in our case.
The 11B and 10B nuclear spin-lattice relaxation rate (1/T1) measurements are able to explore
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the band structure and Fermi surface characteristics of the Zr1-xYxB12 series. The T1 values were
obtained by fitting the saturation recovery data to a single exponential function (Figure 11). The
11B T1 values were 3.12 ± 0.04 s (ZrB12), 4.29 ± 0.01 s (Zr0.5Y0.5B12), and 1.34 ± 0.02 s (YB12) at
ambient temperature. The metallic nature (as seen in NMR and resistivity measurements discussed
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below) of the Zr1-xYxB12 series allows, by using the isotropic shift as obtained from the MAS
퐾2푇1푇
experiments and the T1 values at room temperature, to estimate the Korringa ratio,91
푅 ≡ (
)
푆
as a function of the yttrium concentration. The experimental values of the Korringa ratios are equal
to 0.036 sK (ZrB12), 0.126 sK (Zr0.5Y0.5B12), and 0.096 sK (YB12) and are much smaller than unity
(evidence for Fermi-contact interaction with s- states91). This is direct evidence that the detected
frequency shift and relaxation process are not governed by s-type conduction carriers, but other
contributions (p- or d orbitals) play a dominant role.89
In order to investigate the origin of the relaxation mechanism (magnetic or quadrupolar
10
relaxation), we also acquired the B NMR spectrum (Figure 12, top) both at 10 and 17 kHz in
order to identify the isotropic resonance as well as to obtain the 10B T1 value at ambient temperature
(Figure 12, bottom). By using the 10B and 11B NMR nuclear spin-lattice relaxation data, we can
―1
―1
determine the ratios of 10푇1푀 and 10푇1푄 , where ―1 and ―1 is the magnetic (related to the magnetic
푇1푀
푇1푄
―1
1푀
―1
11푇
11푇
1푄
field fluctuations at the nuclear site) and quadrupolar (related to the electric field gradient
―1
1푀
10푇
fluctuations) relaxation rates, respectively.92,93 The
is related to the square of the
―1
1푀
11푇
(훾훾10)2
magnetogyric ratios
that is approximately 0.112. On the other hand, the quadrupolar
11
―1
푄210
푄211
2퐼11 + 3
2퐼10 + 3
10푇
11푇
1푄
character as given by
is related to the ratios of the quadrupole moments,
=
∙
―1
1푄
퐼210(2퐼10 ― 1) 푇1푄(11퐵)
3
. The nuclear spin quantum numbers are
(10B nucleus) and
(11B
∙
퐼10 = 3
퐼11 = 2
퐼211(2퐼11 ― 1)
푇1푄(10퐵)
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―1
푄210
푄211
10푇
1푄
nucleus). Hence, the quadrupolar ratio
is 4.297, and the
is now estimated to be around
―1
1푄
11푇
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0.644. According to the experimental results obtained from the saturation recovery of 10B (Figure
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12, bottom) and 11B NMR spectroscopic data for the Zr0.5Y0.5B12 compound (Figure 11), the ratio
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―1
2
10푇
11푇
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훾10
1
of
is equal to 0.089 (a value closer to
, verifying the magnetic character of the nuclear
(훾 ) )
―1
1
11
spin-lattice relaxation process. Based on all the aforementioned results, the comparative analysis
of the ratio for the two boron isotopes along with the experimental Korringa ratio value indicates
that the boron relaxation process for Zr0.5Y0.5B12 is mainly magnetic and driven by non-s states at
the Fermi level. This result is in agreement with previously reported and our ab initio
calculations86,87 (Figure S22), which predicted that the Fermi level is located in the region of a
plateau in the density of states that is mainly formed by the boron 2p and metal 4d states, while B
2s contribution at the states near the Fermi level is 18-20 times lower than the B 2p contribution
for YB12 and ZrB12 (Figure S22). This is in accordance with the present NMR spectroscopic results,
which also verified the major contribution of the non s-states at the Fermi level of the Zr1-xYxB12
series.
The superconducting properties and metallic character of these metal dodecaborides were
assessed with electrical resistivity (Figure 13) and SQUID magnetometry (Figure S23).
Dodecaborides were reported to exhibit superconducting transition temperatures in the sub 6 K
range.94–97 (Zr0.5Y0.5)B12 (synthesized as (Zr0.5Y0.5):13B, Tc = 2.5 K) does not fall between YB12
(synthesized as Y:13B, Tc ~ 4.5 – 5.0 K) and ZrB12 (synthesized as Zr:13B, Tc ~ 5.5 - 6.0 K)
(Figure 13, Figure S23). This anomalous behavior of the solid solution transition is supported
with both types of measurements. It should be noted that while superconductivity of ZrB12 phase
is well established, it appears that YB12 phase does not superconduct above 2 K, and the observed
Tc is due to the presence of YB6 (Tc ~ 6 - 7 K) in the Y:13B sample.98,99 This is evident, when the
samples of both dodecaborides are prepared at 1:20 boron ratio, which ensures no lower boride
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(ZrB2 or YB6) phases are present. In the case of ZrB12 prepared at both compositions (1:13 and
1:20), the value of Tc, stays the same, while for YB12, prepared at high boron content, the Tc
essentially disappears becoming lower than the measurement limit, 2 K (Figure S23). Additionally,
the residual resistivity at temperatures below Tc for the YB12 sample is substantially higher than
the residual resistivity for ZrB12 and Zr0.5Y0.5B12 indicating presence of a secondary, not-
superconducting phase in the Y-B sample, thus supporting assumption that YB6 and not YB12 is a
superconducting phase. For the (Zr0.5Y0.5)B12, the Tc suppression upon diluting Zr with another
metal is similar to the one observed for the Zr1-xLuxB12 system, which was attributed to the
presence of impurities.95,97 Still, this is one of the rare cases where a known superhard material is
also a superconductor, and Zr0.5Y0.5B12 now joins WB4.2100 and FeB4.101
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CONCLUSIONS
A single-phase, as evident by PXRD, SEM and solid-state NMR spectroscopy, metal dodecaboride,
Zr0.5Y0.5B12, has been synthesized via solid-solution formation. Furthermore, a solid solution of
ZrB12 and UB12 was prepared. The composition and phase purity were established by powder XRD,
SEM/EDS and XPS. The hardness of Zr0.5Y0.5B12 phase is 47.6 ± 1.7 GPa at 0.49 N load, which is
~17% higher compared to its parent compounds, ZrB12 and YB12, having a hardness of 41.6 ± 2.6
and 37.5 ± 4.3 GPa, respectively. The hardness of Zr0.5U0.5B12 is ~54% higher than that of the UB12
parent. In both cases, the hardness increase can be attributed to the solid solution hardening effects.
In addition, carbon was added to the mixed dodecaboride system. It was found that carbon plays
the role of an insoluble impurity and readily forms boron carbide, B4C, playing a role in
“templating” and patterning effects on the resulting surface morphology. Carbon causes the
samples to cool down very rapidly and as such nucleates a large number of small grains. It was
also found that the source of carbon generates similar results as far as phase composition and
surface morphology. The metal oxidation states were investigated by means of XPS, as the
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previous determination was carried out only by fitting high temperature TGA data. The metals
were found to be in a +4 state for Zr, a +3 for Y and a +5/+6 state for U. Due to dodecaborides
being metals, their color phenomenon was investigated using diffuse-reflectance UV-vis
spectroscopy and the color was attributed to the charge-transfer from the 24 atom boron cage to
the metal, similar to KMnO4. The color of the Zr1-xYxB12 solid solution changed from violet for
pure ZrB12 to blue for YB12; however, for U it was found that upon the addition of 25 at% U, the
color disappears and the sample starts to look metallic, suggesting that the corresponding transition
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has moved beyond the visible region. B and B solid-state NMR spectroscopy confirmed the
cubic structure of the dodecaborides as well as the formation and phase purity of the 50/50 at.%
Zr/Y solid solution. Furthermore, it confirmed the metallic character of the dodecaborides and
showed that the boron relaxation process for Zr0.5Y0.5B12 is mainly magnetic and driven by non-s
states at the Fermi level. Metal dodecaborides are known superconductors, with a Tc of ~4.5-6.0
K for ZrB12 and YB12, as determined by resistivity and SQUID measurements; however, it was
found that the solid solution undergoes a suppression of Tc down to ~2.5 K.
SUPPORTING INFORMATION AVAILABLE
Vickers hardness with errors for (Zr1-xYx):Cz:13B, ZrB2, YB6, B4C, ZrC, WC, B4C in boron,
Zr:Cw:13B, Y:Cw:13B; EDS maps for Zr0.5Y0.5B12 and Zr0.5U0.5B12; full PXRD for ZrB2, YB6, B4C,
ZrC, WC, B4C in boron, Zr:Cw:13 B, Y:Cw:13B, (Zr1-xYx):Cz:13 B; optical images for
(Zr0.5Y0.5):Cz:13B (C = B4C, ZrC + B4C, graphite), where x = 0.00, 0.05, 0.25, 0.50, 0.75, 0.95,
1.00, z = 0.0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0, and w = 1.0, 2.0 and 3.0; diffuse-reflectance for CdS, Cr-
metal and KMnO4; high resolution XPS and peak fitting for (Zr0.5Y0.5):13B and (Zr0.25U0.75):20B;
SQUID magnetometry of Zr:13B, Zr:20B, Y:13B, Y:20B and (Zr0.5Y0.5):13B.
CONFLICTS OF INTEREST
There are no conflicts to declare.
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ORCID
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Georgiy Akopov
Wai H. Mak
0000-0001-9399-9850
0000-0002-8342-1382
0000-0002-4068-7260
0000-0003-3128-5363
0000-0002-5677-6970
0000-0002-7541-3286
0000-0003-2732-4155
0000-0003-4676-4885
0000-0003-1152-1912
0000-0003-0345-4924
Dimitrios Koumoulis
Bryan Owens-Baird
Michael T. Yeung
Shannon Lee
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Paula L. Diaconescu
Reza Mohammadi
Kirill A. Kovnir
Richard B. Kaner
ACKNOWLEDGEMENTS
We thank Professor Chong Liu for helpful discussions; and the National Science Foundation
Division of Materials Research, Grant DMR-1506860 and the Dr. Myung Ki Hong Endowed Chair
in Materials Innovation (R.B.K.), a UCLA Graduate Division Dissertation Year Fellowship (G.A.),
Laboratory Research and Development Program of the Ames Laboratory under the U.S.
Department of Energy Contract No. DE-AC02-07CH11358 (G.A. and K.K.), a UCLA Eugene V.
Cota-Robles Fellowship (W.H.M.), the National Science Foundation Grant CHE-1809116
(P.L.D.), and the Virginia Commonwealth University Startup Grant 137422 (R.M.) for financial
support. The NMR spectroscopic research is supported by the National Science Foundation MRI
program Grant No. 1532232 (R.B.K.). We thank Zachary Hern for help with the uranium metal
wire and Gourab Bhaskar for help with sample preparation for resistivity measurements.
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REFERENCES
4
5
6
7
8
9
(1)
(2)
(3)
Akopov, G.; Yeung, M. T.; Kaner, R. B. Rediscovering the Crystal Chemistry of Borides.
Adv. Mater. 2017, 29, 1604506.
Lundström, T. Borides: Solid-State Chemistry. In Encyclopedia of Inorganic Chemistry;
2006; pp 481–494.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Samsonov, G. V.; Markovskii, L. Y.; Zhigach, A. F.; Valyashko, M. G. Boron, Its
Compounds and Alloys [in Russian]; House of the Academy of the Sciences Ukrainian
SSR: Kiev, 1960.
(4)
(5)
(6)
(7)
(8)
Samsonov, G. V.; Vinitskii, I. M. Refractory Compounds [in Russian]; Atomizdat:
Moscow, 1975.
Samsonov, G. V.; Serebriakova, T. I.; Neronov, V. A. Borides [in Russian]; Atomizdat:
Moscow, 1975.
Buschow, K. H. J. Magnetic Properties of Borides. In Boron and Refractory Borides;
Matkovich, V. I., Ed.; Springer Berlin Heidelberg: Berlin, 1977; pp 494–515.
Scheifers, J. P.; Zhang, Y.; Fokwa, B. P. T. Boron: Enabling Exciting Metal-Rich
Structures and Magnetic Properties. Acc. Chem. Res. 2017, 50, 2317–2325.
Park, H.; Encinas, A.; Scheifers, J. P.; Zhang, Y.; Fokwa, B. P. T. Boron-Dependency of
Molybdenum Boride Electrocatalysts for the Hydrogen Evolution Reaction. Angew.
Chemie - Int. Ed. 2017, 56, 5575–5578.
(9)
Jothi, P. R.; Zhang, Y.; Yubuta, K.; Culver, D.; Conley, M. P.; Fokwa, B. P. T. Abundant
Vanadium Diboride with Graphene-like Boron Layers for Hydrogen Evolution. ACS Appl.
Energy Mater. 2019, 2, 176–181.
(10) Fokwa, B. P. T. Borides: Solid-State Chemistry. Encycl. Inorg. Bioinorg. Chem. 2014, 1–
14.
(11) Akopov, G.; Pangilinan, L. E. L. E.; Mohammadi, R.; Kaner, R. B. R. B. Superhard Metal
21
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Journal of the American Chemical Society
Page 22 of 54
1
2
3
Borides: A Look Forward. APL Mater. 2018, 6, 070901.
4
5
6
7
(12) Yeung, M. T.; Mohammadi, R.; Kaner, R. B. Ultraincompressible, Superhard Materials.
Annu. Rev. Mater. Res. 2015, 46, 465–485.
8
9
(13) Tergenius, L. E. L. E. Refinement of the Crystal Structure of Orthorhombic Mn2B
(Formerly Denoted Mn4B). J. Less-Common Met. 1981, 82, 335–340.
(14) Yeung, M. T.; Akopov, G.; Lin, C.-W. W.; King, D. J.; Li, R. L.; Sobell, Z. C.;
Mohammadi, R.; Kaner, R. B. Superhard W0.5Ta0.5B Nanowires Prepared at Ambient
Pressure. Appl. Phys. Lett. 2016, 109, 203107.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(15) Yeung, M. T.; Lei, J.; Mohammadi, R.; Turner, C. L.; Wang, Y.; Tolbert, S. H.; Kaner, R.
B. Superhard Monoborides: Hardness Enhancement through Alloying in W1−xTaxB. Adv.
Mater. 2016, 28, 6993–6998.
(16) Post, B.; Glaser, F. W.; Moskowitz, D. Transition Metal Diborides. Acta Metall. 1954, 2,
20–25.
(17) Pangilinan, L. E.; Turner, C. L.; Akopov, G.; Anderson, M.; Mohammadi, R.; Kaner, R.
B. Superhard Tungsten Diboride-Based Solid Solutions. Inorg. Chem. 2018, 57, 15305–
15313.
(18) Knappschneider, A.; Litterscheid, C.; Brgoch, J.; George, N. C.; Henke, S.; Cheetham, A.
K.; Hu, J. G.; Seshadri, R.; Albert, B. Manganese Tetraboride, MnB4: High-Temperature
Crystal Structure, p-n Transition, 55Mn NMR Spectroscopy, Solid Solutions, and
Mechanical Properties. Chem. - A Eur. J. 2015, 21, 8177–8181.
(19) Akopov, G.; Roh, I.; Sobell, Z. C.; Yeung, M. T.; Pangilinan, L.; Turner, C. L.; Kaner, R.
B. Effects of Variable Boron Concentration on the Properties of Superhard Tungsten
Tetraboride. J. Am. Chem. Soc. 2017, 139, 17120–17127.
(20) Akopov, G.; Yeung, M. T.; Roh, I.; Sobell, Z. C.; Yin, H.; Mak, W. H.; Khan, S. I.;
Kaner, R. B. Effects of Dodecaboride-Forming Metals on the Properties of Superhard
22
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Journal of the American Chemical Society
1
2
3
Tungsten Tetraboride. Chem. Mater. 2018, 30.
4
5
6
7
(21) La Placa, S.; Binder, I.; Post, B. Binary Dodecaborides. J. Inorg. Nucl. Chem. 1961, 18,
113–117.
8
9
(22) Tanaka, T.; Otani, S.; Ishizawa, Y. Preparation of Single Crystals of YB66. J. Cryst.
Growth 1985, 73, 31–36.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(23) Crespo, A. J.; Tergenius, L. E.; Lundström, T. The Solid Solution of 4d, 5d and Some p
Elements in β Rhombohedral Boron. J. Less-Common Met. 1981, 77, 147–150.
(24) Andersson, S.; Lundström, T. The Solubility of Chromium in β-Rhombohedral Boron as
Determined in CrB∼41 by Single-Crystal Diffractometry. J. Solid State Chem. 1970, 2,
603–611.
(25) Akopov, G.; Yin, H.; Roh, I.; Pangilinan, L. E.; Kaner, R. B. Investigation of Hardness of
Ternary Borides of the YCrB4,Y2ReB6, Y3ReB7, and YMo3B7 Structural Types. Chem.
Mater. 2018, 30, 6494–6502.
(26) Akopov, G.; Yeung, M. T.; Sobell, Z. C.; Turner, C. L.; Lin, C. W.; Kaner, R. B.
Superhard Mixed Transition Metal Dodecaborides. Chem. Mater. 2016, 28, 6605–6612.
(27) Akopov, G.; Yeung, M. T.; Turner, C. L.; Li, R. L.; Kaner, R. B. Stabilization of HfB12 in
Y1-XHfxB12 under Ambient Pressure. Inorg. Chem. 2016, 55, 5051–5055.
(28) Akopov, G.; Roh, I.; Sobell, Z. C.; Yeung, M. T. M. T.; Kaner, R. B. R. B. Investigation
of Ternary Metal Dodecaborides (M1M2M3)B12 (M1, M2 and M3 = Zr, Y, Hf and Gd).
Dalton Trans. 2018, 47, 6683–6691.
(29) Akopov, G.; Sobell, Z. C.; Yeung, M. T.; Kaner, R. B. Stabilization of LnB12 (Ln = Gd,
Sm, Nd, and Pr) in Zr(1– x)Ln(x)B12 under Ambient Pressure. Inorg. Chem. 2016, 55,
12419–12426.
(30) Troć, R.; Wawryk, R.; Pikul, A.; Shitsevalova, N. Physical Properties of Cage-like
Compound UB12. Philos. Mag. 2015, 95, 2343–2363.
23
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Journal of the American Chemical Society
Page 24 of 54
1
2
3
4
5
6
7
(31) Liang, Y.; Zhang, Y.; Jiang, H.; Wu, L.; Zhang, W.; Heckenberger, K.; Hofmann, K.;
Reitz, A.; Stober, F. C.; Albert, B. Thermodynamic Ground States of Multifunctional
Metal Dodecaborides. Chem. Mater. 2019, 31, 1075–1083.
8
9
(32) Paderno, Y.; Shitsevalova, N. Stabilization of Cubic Scandium Dodecaboride. J. Alloys
Compd. 1995, 219, 119–123.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(33) Hamada, K.; Wakata, M.; Sugii, N.; Matsuura, K.; Kubo, K.; Yamauchi, H. Structural
Phase Transition in the Zr1−xScxB12 System. Phys. B Condens. Matter 1994, 194–196,
P, 443–444.
(34) Cannon, J. F.; Cannon, D. M.; Tracy Hall, H. High Pressure Syntheses of SmB2 and
GdB12. J. Less-Common Met. 1977, 56, 83–90.
(35) Cannon, J. F.; Farnsworth, P. B. High Pressure Syntheses of ThB12 and HfB12. J. Less
Common Met. 1983, 92, 359–368.
(36) Portnoi, K. I. I.; Romashev, V. M.; Burobina, L. N.; Romashov, V. M.; Burobina, L. N.
Constitution Diagram of the System Zirconium-Boron. Powder Metall. Met. Ceram. 1970,
7, 68–71.
(37) Liao, P. K.; Spear, K. E. The B-Y (Boron-Yttrium) System. J. Phase Equilib. 1995, 16,
521–524.
(38) Paderno, Y. B.; Adamovskii, A. A.; Lyashchenko, A. B.; Paderno, V. N.; Fillipov, V. B.;
Naydich, Y. V. Zirconium Dodecaboride-Based Cutting Material. Powder Metall. Met.
Ceram. 2004, 43, 546–548.
(39) Okamoto, H. B-C (Boron-Carbon). J. Phase Equilibria 1992, 13, 436.
(40) Sologub, O.; Michiue, Y.; Mori, T. Boron Carbide, B13-x C2-y (x = 0.12, y = 0.01). Acta
Crystallogr. Sect. E Struct. Reports Online 2012, 68, 1–6.
(41) Okamoto, H. C-Zr (Carbon-Zirconium). J. Phase Equilibria 1996, 17, 162.
(42) Lutterotti, L.; Matthies, S.; Wenk, H. R.; Schultz, A. S.; Richardson, J. W. Combined
24
ACS Paragon Plus Environment

Page 25 of 54
Journal of the American Chemical Society
1
2
3
4
5
Texture and Structure Analysis of Deformed Limestone from Time-of-Flight Neutron
Diffraction Spectra. J. Appl. Phys. 1997, 81, 594–600.
6
7
8
9
(43) Lutterotti, L.; Chateigner, D.; Ferrari, S.; Ricote, J. Texture, Residual Stress and Structural
Analysis of Thin Films Using a Combined X-Ray Analysis. Thin Solid Films 2004, 450,
34–41.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(44) Lutterotti, L.; Bortolotti, M.; Ischia, G.; Lonardelli, I.; Wenk, H. R. Rietveld Texture
Analysis from Diffraction Images. Zeitschrift fur Krist. Suppl. 2007, 1, 125–130.
(45) Lutterotti, L. Maud Rev. 2.55. Univ. Trento-Italy, Dep. Ind. Eng. Trento, Italy 2015.
(46) Lutterotti, L. Total Pattern Fitting for the Combined Size-Strain-Stress-Texture
Determination in Thin Film Diffraction. Nucl. Instruments Methods Phys. Res. Sect. B
Beam Interact. with Mater. Atoms 2010, 268, 334–340.
(47) Turner, C. L.; Zujovic, Z.; Koumoulis, D.; Taylor, R. E.; Kaner, R. B. Microscopic
Investigation of Local Structural and Electronic Properties of Tungsten Tetraboride: A
Superhard Metallic Material. J. Mater. Sci. 2019, 54, 3547–3557.
(48) Jaeger, C.; Hemmann, F. EASY: A Simple Tool for Simultaneously Removing
Background, Deadtime and Acoustic Ringing in Quantitative NMR Spectroscopy. Part II:
Improved Ringing Suppression, Application to Quadrupolar Nuclei, Cross Polarisation
and 2D NMR. Solid State Nucl. Magn. Reson. 2014, 63, 13–19.
(49) Yesinowski, J. P. Finding the True Spin-Lattice Relaxation Time for Half-Integral Nuclei
with Non-Zero Quadrupole Couplings. J. Magn. Reson. 2015, 252, 135–144.
(50) Harris, R. K.; Becker, E. D.; Cabral De Menezes, S. M.; Goodfellow, R.; Granger, P.
NMR Nomenclature: Nuclear Spin Properties and Conventions for Chemical Shifts
(IUPAC Recommendations 2001). Concepts Magn. Reson. Part A Bridg. Educ. Res. 2002,
14, 326–346.
(51) Bishop, M.; Shahid, N.; Yang, J.; Barron, A. R. Determination of the Mode and Efficacy
25
ACS Paragon Plus Environment

Journal of the American Chemical Society
Page 26 of 54
1
2
3
4
5
6
7
of the Cross-Linking of Guar by Borate Using MAS11B NMR of Borate Cross-Linked
Guar in Combination with Solution11B NMR of Model Systems. Dalton Trans. 2004, No.
17, 2621–2634.
8
9
(52) Jepsen, O.; Burkhardt, A.; Andersen, O. K. The Program TB-LMTO-ASA, Version 4.7.
Max-Planck-Institut fur Festkorperforschung: Stuttgart, Germany 1999.
(53) Renosto, S. T.; Corrêa, L. E.; da Luz, M. S.; Rosa, P. F. S.; Fisk, Z.; Albino-Aguiar, J.;
Machado, A. J. S. Superconductivity in the Th0.93Zr0.07B12 Compound with UB12
Prototype Structure. Phys. Lett. A 2015, 379, 2498–2501.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(54) Akopov, G.; Yeung, M. T.; Turner, C. L.; Mohammadi, R.; Kaner, R. B. Extrinsic
Hardening of Superhard Tungsten Tetraboride Alloys with Group 4 Transition Metals. J.
Am. Chem. Soc. 2016, 138, 5714–5721.
(55) Akopov, G.; Yeung, M. T.; Roh, I.; Sobell, Z. C.; Yin, H.; Mak, W. H.; Khan, S. I.;
Kaner, R. B. Effects of Dodecaboride Forming Metals on the Properties of Superhard
Tungsten Tetraboride. Chem. Mater. 2018, 30, 3559–3570.
(56) Mohammadi, R.; Xie, M.; Lech, A. T.; Turner, C. L.; Kavner, A.; Tolbert, S. H.; Kaner,
R. B. Toward Inexpensive Superhard Materials: Tungsten Tetraboride-Based Solid
Solutions. J. Am. Chem. Soc. 2012, 134, 20660–20668.
(57) Hume-Rothery, W.; Powell, H. M. On the Theory of Super-Lattice Structures in Alloys. Z.
Krist. 1935, 91, 23.
(58) Hume-Rothery, W.; Smallman, R. W.; Haworth, C. W. The Structure of Metals and
Alloys; The Institute of Metals: London, 1969.
(59) Hume-Rothery, W. Atomic Theory for Students of Metallurgy, 5th ed.; The Institute of
Metals: London, 1969.
(60) Slater, J. C. Atomic Radii in Crystals. J. Chem. Phys. 1964, 41, 3199–3204.
(61) Pauling, L. The Nature of the Chemical Bond. IV. The Energy of Single Bonds and the
26
ACS Paragon Plus Environment

Page 27 of 54
Journal of the American Chemical Society
1
2
3
4
5
6
7
8
9
Relative Electronegativity of Atoms. J. Am. Chem. Soc. 1932, 54, 3570–3582.
(62) Pauling, L. Nature of the Chemical Bond, 3rd ed.; Cornell University Press: Ithaca, 1960.
(63) Mar, R. W.; Stout, N. D. High Temperature Enthalpies of Binary Dodecaborides. J. Chem.
Phys. 1972, 57, 5342–5349.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(64) Vegard, L. Die Konstitution Der Mischkristalle Und Die Raumfullung Der Atome.
Zeitschrift fur Phys. 1921, 5, 17–26.
(65) Mansouri Tehrani, A.; Oliynyk, A. O.; Parry, M.; Rizvi, Z.; Couper, S.; Lin, F.; Miyagi,
L.; Sparks, T. D.; Brgoch, J. Machine Learning Directed Search for Ultraincompressible,
Superhard Materials. J. Am. Chem. Soc. 2018, 140, 9844–9853.
(66) McCaughey, C.; Tsakiropoulos, P. Type of Primary Nb5Si3and Precipitation of Nbssin
ΑNb5Si3in a Nb-8.3Ti-21.1Si-5.4Mo-4W-0.7Hf (at.%) near Eutectic Nb-Silicide-Based
Alloy. Materials (Basel). 2018, 11, 1–25.
(67) Lei, J.; Akopov, G.; Yeung, M. T.; Yan, J.; Kaner, R. B.; Tolbert, S. H. Radial X-Ray
Diffraction Study of Superhard Early Transition Metal Dodecaborides under High
Pressure. Adv. Funct. Mater. 2019, 1900293.
(68) Li, Y.; Bushby, A. J.; Dunstan, D. J. The Hall–Petch Effect as a Manifestation of the
General Size Effect. Proc. R. Soc. A Math. Phys. Eng. Sci. 2016, 472, 20150890.
(69) Petch, N. J. The Cleavage Strength of Polycrystals. J. Iron Steel Inst. 1953, 174, 25–28.
(70) Bundy, F. P.; Hall, H. T.; Strong, H. M.; Wentorf, R. H. Man-Made Diamonds. Nature
1955, 176, 51–55.
(71) Bovenkerk, H. P.; Bundy, F. P.; Hall, H. T.; Strong, H. M.; Wentorf, R. H. Preparation of
Diamond. Nature 1959, 184, 1094–1098.
(72) Uwamino, Y.; Ishizuka, T.; Yamatera, H. X-Ray Photoelectron Compounds Spectroscopy
of Rare-Earth. J. Electron Spectros. Relat. Phenomena 1984, 34, 67–78.
(73) Baba, Y.; Sasaki, T. A. Application of X‐ray‐induced Auger Electron Spectroscopy to
27
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Journal of the American Chemical Society
Page 28 of 54
1
2
3
4
5
State Analyses of Hydrogen Implanted in Y, Zr and Nb Metals. Surf. Interface Anal. 1984,
6, 171–173.
6
7
8
9
(74) Anderson, J. A.; Fierro, J. L. G. Bulk and Surface Properties of Copper-Containing Oxides
of the General Formula LaZr1-XCuxO3. Journal of Solid State Chemistry. 1994, pp 305–
313.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(75) Nishino, Y.; Krauss, A. R.; Lin, Y.; Gruen, D. M. Initial Oxidation of Zirconium and
Zircaloy-2 with Oxygen and Water Vapor at Room Temperature. J. Nucl. Mater. 1996,
228, 346–353.
(76) Ilton, E. S.; Bagus, P. S. XPS Determination of Uranium Oxidation States. Surf. Interface
Anal. 2011, 43, 1549–1560.
(77) Samsel-Czekała, M.; Talik, E.; Troć, R.; Shitsevalova, N. Electronic Structure of Cage-
like Compound UB12 - Theory and XPS Experiment. J. Alloys Compd. 2014, 615, 446–
450.
(78) Ejima, T.; Sato, S.; Suzuki, S.; Saito, Y.; Fujimori, S.; Sato, N.; Kasaya, M.;
Komatsubara, T.; Kasuya, T.; Ōnuki, Y. Line Shapes of the XPS U 4f Spectra in Some
Uranium Compounds. Phys. Rev. B - Condens. Matter Mater. Phys. 1996, 53, 1806–1813.
(79) Ma, T.; Li, H.; Zheng, X.; Wang, S.; Wang, X.; Zhao, H.; Han, S.; Liu, J.; Zhang, R.; Zhu,
P.; Long,Y.; Cheng, J.; Ma, Y.; Zhao, Y.; Jin, C.; Yu, X. Ultrastrong Boron Frameworks
in ZrB12: A Highway for Electron Conducting. Adv. Mater. 2017, 29, 1–7.
(80) Tauc, J.; Menth, A. States in the Gap. J. Non. Cryst. Solids 1972, 8–10, 569–585.
(81) Tauc, J. Optical Properties and Electronic Structure of Amorphous Ge and Si. Mater. Res.
Bull. 1968, 3, 37–46.
(82) Tauc, J.; Grigorovici, R.; Vancu, A. Optical Properties and Electronic Structure of
Amorphous Germanium. Phys. Status Solidi 1966, 15, 627–637.
(83) Hecht, H. G. The Interpretation of Diffuse Reflectance Spectra. J. Res. Natl. Bur. Stand. A
28
ACS Paragon Plus Environment

Page 29 of 54
Journal of the American Chemical Society
1
2
3
1976, 80, 567–583.
4
5
6
7
8
9
(84) Kubelka, P. New Contributions to the Optics of Intensely Light-Scattering Materials Part
II: Nonhomogeneous Layers*. J. Opt. Soc. Am. 1948, 38, 330–335.
(85) Kubelka, P.; Munk, F. Ein Beitrag Zur Optik Der Farbanstiche. Z. Techn. Phys. 1931, 12,
593–601.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
(86) Korozlu, N.; Surucu, G. The Electronic and Optical Properties of MB12 (M = Zr, Hf, Y,
Lu) Dodecaboride Compounds. Phys. Scr. 2013, 87.
(87) Shein, I. R.; Ivanovskii, A. L. Band Structure of Superconducting Dodecaborides YB12
and ZrB12. Phys. Solid State 2003, 45, 1429–1434.
(88) Papavassiliou, G.; Pissas, M.; Karayanni, M.; Fardis, M.; Koutandos, S.; Prassides, K.
11B and 27Al NMR Spin-Lattice Relaxation and Knight Shift of Mg(1-x)Al(x)B2
Evidence for an Anisotropic Fermi Surface. Phys. Rev. B - Condens. Matter Mater. Phys.
2002, 66, 1–4.
(89) Winter, J. Magnetic Resonance in Metals, xiii.; Claredon Press: Oxford, 1971.
(90) Carter, G. C.; Bennett, L. H.; Kahan, D. J. Metallic Shifts in NMRꢀ: A Review of the
Theory and Comprehensive Critical Data Compilation of Metallic Materials: Part 2,
Progress in Materials Science (Book 20), 1st ed.; Pergamon Press: Oxford, 1977.
(91) Suh, B. J.; Zong, X.; Singh, Y.; Niazi, A.; Johnston, D. C. B11 NMR in the Layered
Diborides Os B2 and Ru B2. Phys. Rev. B - Condens. Matter Mater. Phys. 2007, 76, 1–4.
(92) Balz, R.; Brändie, U.; Kammerer, E.; Köhnlein, D.; Lutz, O.; Nolle, A.; Schafitel, R.;
Veil, E. 11B and 10B NMR Investigations in Aqueous Solutions. Zeitschrift fur
Naturforsch. - Sect. A J. Phys. Sci. 1986, 41, 737–742.
(93) Brinkmann, D. Quadrupolar Relaxation - What Would We Do without It in High-Tc
Superconductor Studies? Zeitschrift fur Naturforsch. - Sect. A J. Phys. Sci. 2000, 55, 323–
326.
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ACS Paragon Plus Environment