Solid solution range of boron and properties of the perovskite-type NdRh3B

Article abstract of DOI:10.1016/S0925-8388(01)01832-1

Polycrystalline samples of NdRh₃B_x have been synthesized by arc melting technique. The crystal structure of NdRh₃B_x is the perovskite-type cubic system (space group Pm3?m) for nominal boron concentration in the range of 0.706≤x≤1.000 (15-20 mol.% B). The lattice parameter a varies linearly from 0.41749(7) nm (x = 0.706) to a = 0.42136(6) nm (x = 1.000). Thermogravimetric analysis indicates that the oxidation onset temperature for NdRh₃B_1.000 is 663 K. The weight gain of the sample by heating in air up to 1473 K is 10.00% for NdRh₃B_1.000, and oxidized products are Rh and NdBO₃. The micro-Vickers hardness is 4.9±0.05 GPa for NdRh₃B_1.000. NdRh₃B_1.000 shows a metallic temperature dependence of the resistivity down to 0.5 K. Magnetic susceptibilities for NdRh₃B_1.000 show Curie-like paramagnetic temperature dependence due to Nd³⁺ moments. No trace of magnetic phase transitions and superconductivity is found.

Full text of DOI:10.1016/S0925-8388(01)01832-1

Journal of Alloys and Compounds 335 (2002) 191–195
L
www.elsevier.com/locate/jallcom
Solid solution range of boron and properties of the perovskite-type
NdRh B
3
a ,
a
b
c
a
*
Toetsu Shishido , Takahiko Sasaki , Kunio Kudou , Shigeru Okada , Akira Yoshikawa ,
a
d
e
a
f
Jung Min Ko , Jinhua Ye , Iwami Higashi , Masaoki Oku , Hiroyuki Horiuchi ,
a
g
a
Tsuguo Fukuda , Shigemi Kohiki , Kazuo Nakajima
Institute for Materials Research (IMR), Tohoku University, 2-1-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
Department of Mechanical Engineering, Kanagawa University, 3-27-1 Rokkakubashi, Kanagawa-ku, Yokohama 221-8686, Japan
Department of Civil Engineering, Faculty of Engineering, Kokushikan University, 4-28-1, Setagaya-ku, Tokyo 154-0017, Japan
a
b
c
d
National Institute for Materials Science, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan
Department of Chemistry, Chiba Institute of Technology, Shibazono, Narashino, Chiba 275-0023, Japan
Earth Science Laboratory, Faculty of Education, Hirosaki University, 1 Bunkyo-cho, Hirosaki, Aomori 036-8560, Japan
e
f
g
The Kyusyu Institute of Technology, Kita-kyusyu 804-8550, Japan
Received 27 April 2001; received in revised form 13 July 2001; accepted 24 July 2001
Abstract
Polycrystalline samples of NdRh B have been synthesized by arc melting technique. The crystal structure of NdRh B is the
3
x
3
x
]
perovskite-type cubic system (space group Pm3m) for nominal boron concentration in the range of 0.706 # x # 1.000 (15–20 mol.% B).
The lattice parameter a varies linearly from 0.41749(7) nm (x50.706) to a50.42136(6) nm (x51.000). Thermogravimetric analysis
indicates that the oxidation onset temperature for NdRh B
is 663 K. The weight gain of the sample by heating in air up to 1473 K is
3
1.000
1
0.00% for NdRh B
, and oxidized products are Rh and NdBO . The micro-Vickers hardness is 4.960.05 GPa for NdRh B1.000.
3
1.000
3
3
NdRh B
shows a metallic temperature dependence of the resistivity down to 0.5 K. Magnetic susceptibilities for NdRh B
show
3
1.000
3
1.000
3
1
Curie-like paramagnetic temperature dependence due to Nd moments. No trace of magnetic phase transitions and superconductivity is
found. 2002 Elsevier Science B .V . All rights reserved.

Keywords: NdRh B; Microhardness; Oxidation resistance in air; Electric property; Magnetic property
3
1
. Introduction
ErRh B (simple tetragonal system, space group: P42 /nmc,
4 4
a50.5304(1) nm, c50.7395(2) nm). The physical and
chemical properties of these crystals have been reported
[3,4].
Many studies of perovskite-type oxides have been
performed due to the interesting features in the supercon-
ducting transition, the insulator–metallic transition, ion
conduction characteristics, dielectric properties, and fer-
roelasticity. On the other hand, there have been few studies
on non-oxide perovskite-type compounds [5,6].
The rare earth element (RE)–platinum group element–
boron (B) systems have received considerable attention
from many researchers in the fields of crystallography,
magnetism, superconductivity, heavy-electron behaviour
and valence fluctuations. Particularly, the discovery of the
ErRh B compound, which is a re-entrant superconductor,
4
4
has drawn much attention to these ternary systems [1,2].
We have previously prepared single crystals of several
compounds by molten metal flux method, using Cu as a
We have previously prepared RERh B (RE5La, Gd and
3
]
flux. They are ErRh B (cubic system, space group: Pm3m,
Lu) by arc-melting synthetic method [7,8], where La, Gd
and Lu are the first, middle and last elements of the
lanthanoids, in which RE is positioned at the eight corners
of the cube, Rh is face-centered and B is body-centered.
The B-deficient compounds, RERh B , can also be ob-
3
a50.4146 nm), ErRh B (base-centered monoclinic sys-
3
2
tem, ErIr B type, space group: C2/m, a50.5355(1) nm,
3
2
b50.9282(1) nm, c50.3102(1) nm, b590.89(3)8) and
3
x
tained. The B content variation induces changes in the
electromagnetic properties, hardness, and chemical resist-
ance against oxidation in air at high temperature.
*
Corresponding author. Tel.: 181-22-215-2233; fax: 181-22-215-
202.
E-mail address: crystal@imr.tohoku.ac.jp (T. Shishido).
2
0
925-8388/02/$ – see front matter
 2002 Elsevier Science B .V . All rights reserved.
PII: S0925-8388(01)01832-1

1
92
T. Shishido et al. / Journal of Alloys and Compounds 335 (2002) 191–195
In this study, we focused on the less than half element of
method from 0.5 K to room temperature. The magnetic
susceptibility measurements were performed in a field of
5000 Oe using a commercial SQUID magnetometer
(Quantum Design Inc., MPMS-5) from 5 K to room
temperature.
Nd (atomic number 60) in the lanthanoids. We synthesized
the perovskite-type compound NdRh B . The solid solu-
3
x
tion range of boron in the NdRh B is clarified by powder
3
x
X-ray diffraction (XRD) analysis, and the variation of the
lattice constant of the sample is investigated as a function
of the boron concentration x. Vickers microhardness (Hv)
and thermogravimetric and differential thermal analysis
3. Results and discussion
(
TG–DTA) measurements were performed on the samples.
The temperature dependence of the electrical resistance
and magnetization was studied for the samples.
3.1. Appearance and chemical composition of
synthesized material
Since the boiling points of Nd, Rh and B are high at
3373, 4233 and 2823 K, respectively, evaporation can be
neglected [9]. Accordingly, we judge that the arc melting
method is suitable for the synthesis of NdRh B . Samples
2
. Experimental
2
.1. Sample preparation
3
x
of NdRh B obtained by varying the B content x were all
3
x
Polycrystalline samples of NdRh B were synthesized
by the arc melting method using 99.9% pure Nd, Rh and B
as raw materials. These were weighed in the atomic ratio
silver in color and exhibited a metallic lustre. The result of
chemical analysis shows that the chemical compositions
before and after synthesis are almost the same. In addition,
contamination from the electrode (tungsten) and hearth
(copper) could be disregarded in this study.
3
x
1
:3:x, where x51.000 (20 mol.% B), 0.848 (17.5 mol.%
B), 0.706 (15 mol.% B), 0.444 (10 mol.% B), 0.210 (5
mol.% B) and 0 (0 mol.% B). The mixture of the starting
materials, about 2 g for each sample, was placed in a
water-cooled copper hearth in a reaction chamber. Argon
was used as a protective atmosphere. The pressure inside
the chamber was |1 atm. A small amount of residual
oxygen in argon was eliminated by fusing a button of
titanium as a reducing agent. The starting materials were
then melted for 3 min by an argon arc plasma flame with
DC power source at 20 V and 100 A. The samples were
then turned over and melted three times under the same
conditions. Finally, synthesized samples were wrapped in
tantalum foil and annealed at 1573 K for 20 h under
vacuum to ensure homogeneity.
3.2. Relationship between the nonstoichiometry of B and
the lattice constant of NdRh B samples
3
x
The crystal structure analysis on NdRh B samples with
3
x
a B content of x51.000 by powder XRD reveals that it is a
]
perovskite-type compound (space group: Pm3m) in which
Nd is positioned at the eight corners of the cube, Rh is
face-centered and B is body-centered (Fig. 1). By varying
x, the nonstoichiometry of B and the resulting change of
the crystal structure were studied. Fig. 2 shows changes of
2
.2. Characterization
For chemical analysis, the samples were fused using
NaHSO as a flux reagent, then the obtained material was
4
dissolved into HCl. The chemical composition of each
solution was analyzed by the induction coupled plasma
atomic emission spectrometry (ICP–AES) method, using
Zn as internal standard. Crystal structure characterization
of the samples was performed by XRD. The micro-Vickers
hardness for the samples was measured at room tempera-
ture. A load of 100 g was applied for 15 s and 10
impressions were recorded for each sample. The obtained
values were averaged and the experimental error was
estimated. Thermogravimetric analysis and differential
thermal analysis were performed between room tempera-
ture and 1473 K to study the oxidation resistance of the
samples in air. A sample was heated at a rate of 10 K/min
up to 1473 K. The oxidation products were analyzed by
powder X-ray diffractometry. The electrical resistivity of
the samples was measured by means of a DC four probe
Fig. 1. Arrangement of atoms in the perovskite-type NdRh B. Large
gray, large open and small black circles represent Nd, Rh and B atoms,
respectively.
3

T. Shishido et al. / Journal of Alloys and Compounds 335 (2002) 191–195
193
Table 1
Lattice parameter of the NdRh B
3
x
Sample (at.%
of boron)
Lattice
parameter
a, nm
Error
nm
NdRh B
(20)
(17.5)
(15)
(10)
(5)
0.41236
0.41927
0.41749
0.4179
0.00006
0.00008
0.00007
0.0001
3
1.000
0.848
0.706
0.444
0.210
NdRh B
3
NdRh B
3
NdRh B
3
NdRh B
0.4175
0.0001
3
while, according to our experimental results for LaRh B ,
3
x
the perovskite-type compound does not have B-nonstoich-
iometry, which indicates that x51. In the case of GdRh B
Fig. 2. Powder XRD profiles for NdRh B with x51.000, x50.8484,
3
x
3
x
x50.706, x50.444, x50.210 and x50. These are nominal compositions.
In the cases of x50.706, x50.444 and x50.210, a mixture phase of
NdRh B and NdRh3 is formed.
and LuRh B , B-nonstoichiometry ranges within 0.55 #
3 x
x # 1.00 and 0.30 # x # 1.00, respectively. The aforemen-
tioned results are listed in Table 2. As shown in Table 2, B
exhibits no nonstoichiometry in the case of RE5La. La
has the largest atomic radius among all the RE elements,
while B gradually became nonstoichiometric as the atomic
radius is decreased in the order of Nd, Gd and Lu.
Electronegativity of the RE elements changes from 1.1
(La) to 1.2 (Lu). Electronegativity of the RE atoms seems
to also affect boron nonstoichiometry of the RERh B .
3
x
the powder XRD patterns when x is varied. With decreas-
ing x, the XRD peaks of the perovskite-type phase are
shifted to higher angles. In the cases of x50.706, 0.444
and 0.210, two phases of NdRh B and NdRh3 are
3
x
observed.
3
x
Fig. 3 shows the relationship between x and the lattice
constant of NdRh B . The lattice constant changes almost
3.3. Relationship between B content and hardness in
3
x
linearly with x, varying from 0.41749(7) nm (x50.706) to
a50.42136(6) nm (x51.000). Table 1 shows the lattice
parameters of the NdRh B . Accordingly, NdRh B exists
NdRh B
3
x
We studied the hardness of NdRh B , which reflects the
3
x
3
x
3
x
in a nonstoichiometric range of 0.706 # x # 1.000. Mean-
nature of the chemical bonding. Table 3 shows that the
microhardness of the compound is 4.360.2 and 4.960.05
GPa when x50.848 and 1.000, respectively. In a previous
Table 2
Boron nonstoichiometry in the RERh B (RE5La, Nd, Gd, Lu)
3
x
RERh B
Boron nonstoichiometry
Reference
3
x
RE
range of x
La
Nd
Gd
Lu
x51
[8]
This study
[7]
[8]
0.71 # x # 1
0.55 # x # 1
0.30 # x # 1
Table 3
Vickers hardness of the NdRh B
3
x
Sample
Hardness,
GPa
(at.% of boron)
a
NdRh B
(20)
4.960.05
4.360.2
3
1.000
a
NdRh B
(17.5)
3
0.848
b
RhB (50)
12.1
7.8
b
Rh B (30)
7
3
a
Fig. 3. The variation of lattice constant a as a function of boron
concentration x in NdRh B .
Cubic system.
Hexagonal system.
b
3
x

1
94
T. Shishido et al. / Journal of Alloys and Compounds 335 (2002) 191–195
study, as shown in Table 3, the value of microhardness for
an Rh–B binary system increased with boron content of
the compound [10]. This tendency of binary borides is
essentially in agreement with our data on ternary borides.
We then focused on only stoichiometric RERh B1.000. The
3
hardness in the series of RE5La, Nd, Gd and Lu is listed
in Table 4. Hardness increases with decreasing atomic size
of the RE in RERh B1.000; it became greater with increas-
3
ing density of itself. In all cases of RE5La, Nd, Gd and
Lu, hardness of the compound decreases with decreasing
the boron content x in RERh B . In GdRh B , for exam-
3
x
3
x
ple, boron nonstoichiometry ranges between 0.55 # x # 1
and hardness changes from 4.060.1 to 6.860.1 GPa,
respectively.
3
.4. Resistance to oxidation of NdRh B
3 1.000
We studied how the resistance to oxidation in air, which
reflects the nature of the chemical bonds of the compound,
varied with the B content. Samples were heated up to 1473
K in air and subjected to thermogravimetric and differen-
tial thermal analyses (TG–DTA). As shown in Fig. 4, TG
analysis reveals that oxidation begins at 663 K. Maximum
weight gains due to oxidation are 11.76% at 1223 K. Final
weight gains are 10.00% at 1473 K. A volatile matter, for
example B O , seems to be formed above 1223 K. DTA
2
3
reveals exothermic peaks at 823 and 927 K. A study of
oxidized products by the powder XRD method shows that
the products are Rh and NdBO . The results of TG–DTA
3
are listed in Table 5.
Fig. 4. TG–DTA curves for NdRh B1.000.
3
3
.5. Resistivity and magnetic susceptibility of
calculated to be about 3.5 from the initial slope. This value
is close to the theoretical one (3.62) of Nd ion.
3
1
NdRh B
3
1.000
Fig. 5 shows the temperature dependence of the electric
resistivity of NdRh B1.000. The sample measured exhibits
3
metallic behaviour from room temperature down to 0.5 K.
No superconductivity appears at the lowest temperature.
Fig. 6 shows the temperature dependence of the mag-
4. Conclusions
1. Polycrystalline samples of NdRh B have been syn-
3
x
netization of NdRh B
netic susceptibilities for NdRh B
paramagnetic behavior. No trace of magnetic phase transi-
tions and superconductivity is found down to 0.5 K. The
inset shows the linear temperature dependence of the
inverse susceptibility. The effective Bohr magneton is
in a field H55000 Oe. Mag-
thesized by arc melting method.
2. The structure of the NdRh B is the perovskite-type
1.000
3
1.000
show Curie-like
3
1.000
3
]
cubic system (space group Pm3m) and this phase exists
in the range of 0.706 # x # 1.000 (15–20 at.% B). The
lattice parameter a varies linearly from 0.41749(7) nm
(x50.706) to a50.42136(6) nm (x51.000).
3
. By means of TG–DTA between room temperature and
1473 K, the oxidation of the compound in air starts at
Table 4
Vickers hardness of the RERh B
3
1.000
Sample
Hardness
GPa
Atomic radius
of RE (nm)
Density
g/cm
Reference
3
Table 5
RERh B
3
1.000
Results of the TG–DTA measurements for the NdRh B
3
1.000
RE
Sample
Oxidation
onset (K)
Exotherm
maximum
Weight
gain
(%)
Oxidation
products
La
Nd
Gd
Lu
4.260.1
4.960.05
6.860.1
7.760.5
0.188
0.182
0.180
0.174
9.91
10.30
10.82
11.69
[8]
This study
[7]
[8]
(
K)
NdRh B
663 K
823, 927
10.00
Rh1NdBO3
3
1.000

T. Shishido et al. / Journal of Alloys and Compounds 335 (2002) 191–195
195
6
63 K and the final weight gain is 10.00%. The mixed
phase of Rh and NdBO3 is identified by XRD as a
resultant product.
4
5
6
. The micro-Vickers hardness is 4.960.05 GPa for
NdRh B1.000.
3
. NdRh B
shows a metallic temperature dependence
3
1.000
of the resistivity down to 0.5 K.
. Magnetic susceptibilities for NdRh B
show Curie-
1.000
3
3
1
like paramagnetic behaviour due to Nd moment. No
trace of magnetic phase transitions and superconductivi-
ty is found down to 5 K.
Acknowledgements
This work was performed under the inter-university
cooperative research program of the Laboratory for Ad-
vanced Materials (LAM), Institute for Materials Research
(
IMR), Tohoku University. The authors are grateful to Dr.
K. Takada and Messrs. K. Obara, T. Sugawara, K. Sasaki,
S. Tozawa, T. Takahashi, Y. Murakami and M. Ishikuro of
IMR, Tohoku University, for help during sample prepara-
tions and chemical analyses.
Fig. 5. Temperature dependence of the electric resistivity of
NdRh B1.000.
3
References
[1] L.D. Woolf, D.C. Johnston, H.B. MacKay, R.W. McCallum, M.B.
Maple, J. Low Temp. Phys. 35 (1979) 651.
[
2] For a review, see Superconductivity in ternary compounds II, in:
M.B. Maple, O. Fisher (Eds.), Topics in Current Physics, Vol. 34,
Springer, Berlin, 1982.
[3] T. Shishido, I. Higashi, H. Kitazawa, J. Bernhard, H. Takei, T.
Fukuda, Boron, borides and related compounds, Jpn. J. Appl. Phys.
1
0 (Special issue) (1994) 142.
[4] T. Shishido, K. Kudou, S. Okada, Y. Ye, M. Oku, H. Horiuchi, T.
Fukuda, J. Alloys Comp. 280 (1998) 65.
[
[
[
5] H. Holleck, J. Less-Common Metals 52 (1977) 167.
6] P. Rogl, L. Delong, J. Less-Common Metals 91 (1983) 97–102.
7] T. Shishido, J. Ye, K. Kudou, S. Okada, K. Obara, T. Sugawara, M.
Oku, K. Wagatsuma, H. Horiuchi, T. Fukuda, J. Alloys Comp. 291
(
1999) 52.
[
8] T. Shishido, J. Ye, K. Kudou, S. Okada, M. Oku, H. Horiuchi, T.
Fukuda, J. Ceram. Soc. Jpn. 108 (7) (2000) 683.
9] R.E. Honig, RCA Rev. 23 (1962) 571.
[
[10] G .V . Samsonov, I.M. Vinitskii, in: Handbook of Refractory Com-
pounds, IFI/Plenum Press, New York, 1980, p. 303.
Fig. 6. Temperature dependence of the magnetization of NdRh B
in
1.000
3
H55000 Oe. The inset shows the temperature dependency of inverse
susceptibility.