Structure, properties, and bonding of ZrTe (MnP type), a low-symmetry, high-temperature modification of ZrTe (WC type)

Article abstract of DOI:10.1021/ja004164r

ZrTe (MnP) was synthesized by high-temperature methods at 1570 K in Ta ampules. The structure of the telluride was determined by means of single-crystal X-ray diffraction to be orthorhombic, Pnma (No. 62), Z = 4, Pearson Symbol oP8, a = 739.15(15) pm, b =

Full text of DOI:10.1021/ja004164r

4168
J. Am. Chem. Soc. 2001, 123, 4168-4173
Structure, Properties, and Bonding of ZrTe (MnP Type), a
Low-Symmetry, High-Temperature Modification of ZrTe (WC Type)
Gissur O2 rlygsson and Bernd Harbrecht*
Contribution from the Department of Chemistry and Materials Science Centre, Philipps UniVersity,
Hans-Meerwein-Strasse, D-35032 Marburg, Germany
ReceiVed December 4, 2000
Abstract: ZrTe (MnP) was synthesized by high-temperature methods at 1570 K in Ta ampules. The structure
of the telluride was determined by means of single-crystal X-ray diffraction to be orthorhombic, Pnma (No.
62), Z ) 4, Pearson Symbol oP8, a ) 739.15(15) pm, b ) 377.23(8) pm, c ) 694.34(14) pm. The orthorhombic
MnP type structure is a distorted variant of the NiAs type structure with pronounced metal-metal zigzag
chains. Zigzag chains are typical for phases with a d2 metal atom electron configuration. According to extended
Hu¨ckel calculations, the homonuclear interactions in the zigzag chains make up for 2/3 of the Zr-Zr interactions
in ZrTe (MnP) and contribute decisively to the stability of the structure. The emergence of the distorted MnP
type structure instead of the high-symmetry NiAs type ZrTe at high temperatures can be understood as the
result of an optimization of homonuclear Zr-Zr interactions arising from states close to the Fermi level. The
hexagonal WC type ZrTe transforms above 1438 ( 5 K into ZrTe (MnP) (∆H ) 8.3 ( 1.0 kJ mol-1). The
phase transition is reversible, although at room-temperature the reverse reaction is kinetically inhibited. Zr5-
Te4 and Zr5Te6 are the phases next to ZrTe. ZrTe (MnP) exhibits temperature-independent paramagnetic
properties (ømol ) 0.14 × 10-3 cm3 mol-1), as typical for a metallic conductor. Resistivity measurements on
ZrTe (MnP) imply metallic behavior.
Introduction
second modification of phases of the NiAs type, e.g., for VS,6,7
TiSe,3,8 and CrAs,9 in which the NiAs type corresponds to the
high-temperature form. On the opposite side, NbS stabilizes at
high temperatures in the MnP type, whereas at lower temper-
atures a hexagonal NiAs type superstructure exists.10 In FeS,
the MnP type structure can be induced through the application
of high pressure.11 Variations in stoichiometry apparently play
a certain role in at least some of those phase transitions, e.g.,
ref 7.
The study of phase transitions between structurally simple
solid-state compounds offers interesting opportunities to gain
insight into the factors stabilizing each phase and thereby into
the driving forces underlying the structural changes. Binary,
equiatomic phases are in this regard the ideal candidates, second
only to the elements themselves.
The structure type pairs NaCl-WC, MnP-NiAs, and NiAs-
WC, for example, belong to this category. Transition-metal
carbides and nitrides often crystallize in the NaCl or the WC
type structures. Theoretical calculations have shown that the
valence-electron count per unit cell has a significant impact on
the preference for one or the other of the two structure types.1
A close relationship between structure and valence-electron
count is also observed in transition-metal phosphides. In those
compounds the driving force for transitions between NiAs and
MnP type phases was found to be a second-order Jahn-Teller-
like distortion.2 The role of the valence-electron concentration
has been substantiated in experiments in the ternary chalco-
genide system Ti-V-S. Thus, as a result of a reduction in
In recent years, a number of new phases have been discovered
in the system Zr-Te. In the metal-rich part of the system, Zr3-
Te12 and Zr2Te13 were characterized, whereas on the tellurium-
rich side, Zr5Te614 and Zr1.3Te215 were identified. Furthermore,
a reinvestigation of the phase diagram was carried out lately.16
We report here on a new, binary zirconium telluride crystallizing
in the MnP type structure. It represents a high-temperature
modification of ZrTe. The low-temperature form crystallizes
in the well-known WC type structure.17,18 To our knowledge, a
WC-MnP type phase transition has not been reported before.
On this ground, and due to the structural simplicity of both
compounds, we also have embarked on a study of the phase
valence-electron concentration from 11 to ca. 10.5, TixV1-x
S
transforms from the MnP type to the NiAs type when x lies
above ca. 0.5.3,4
(6) Franzen, H. F.; Wiegers, G. A. J. Solid State Chem. 1975, 13, 114.
(7) Silvestre, J.; Tremel, W.; Hoffmann, R. J. Less-Common Metals 1986,
116, 113.
The MnP type structure5 can be seen as an orthorhombically
distorted variant of the NiAs type structure with pronounced
metal atom zigzag chains. The MnP type often represents a
(8) Grønvold, F.; Langmyhr, F. J. Acta Chem. Scand. 1961, 15, 1949.
(9) Selte, K.; Kjekshus, A. Acta Chem. Scand. 1973, 27, 3195.
(10) Kadijk, F.; Jellinek, F. J. Less-Common Metals 1969, 19, 421.
(11) King, H. E., Jr.; Prewitt, C. T. Acta Crystallogr. 1982, B38, 1877.
(12) Harbrecht, B.; Leersch, R. J. Alloys Compd. 1996, 238, 13.
(13) O¨ rlygsson, G.; Harbrecht, B. Inorg. Chem. 1999, 38, 3377.
(14) O¨ rlygsson, G.; Harbrecht, B. Chem. Eur. J. 2000, 6, 4170.
(15) Wang, C.; Eylem, C.; Hughbanks, T. Inorg. Chem. 1998, 37, 390.
(16) de Boer, R.; Cordfunke, E. H. P. J. Alloys Compd. 1997, 259, 115.
(17) Bratta˚s, L.; Kjekshus, A. Acta Chem. Scand. 1971, 25, 2350.
(18) O¨ rlygsson, G.; Harbrecht, B. Z. Naturforsch. 1999, 54b, 1125.
(1) Wijeyesekera, S. D.; Hoffmann, R. Organometallics 1984, 3, 949.
(2) Tremel, W.; Hoffmann, R.; Silvestre, J. J. Am. Chem. Soc. 1986,
108, 5174.
(3) Henderson Lewis, L.; Goodenough, J. B. J. Solid State Chem. 1995,
114, 346.
(4) Franzen, H. F.; Leebrick, D. H.; Laabs, F. J. Solid State Chem. 1975,
13, 307.
(5) Rundqvist, S. Acta Chem. Scand. 1962, 16, 287.
10.1021/ja004164r CCC: $20.00 © 2001 American Chemical Society
Published on Web 04/13/2001

Structure, Properties, and Bonding of ZrTe
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4169
transition and the factors governing the relative stability of each
phase, as well as on a study of the structure-property relations.
Experimental Section
Preparation. Due to the air-sensitivity of the tellurides, they were
stored and handled under argon. The starting material ZrTe2 was
prepared from the elements (Te 99.999%, Fluka; Zr 99.8%, ChemPur,
nZr:nTe ) 1:2) in previously outgassed, sealed quartz glass tubes (1150
K, 1 d). Single crystals of ZrTe (MnP) were obtained through the
reduction of ZrTe2 with Zr (nZr:nTe ) 1:1; 1570 K, 3 d, I2) in a sealed,
argon-filled tantalum tube, which in turn was contained in an evacuated
corundum tube (P < 10-3 Pa). The temperature of the reaction mixture
was uniformly raised at 100 K h-1 to 1570 K, and lowered again at
150 K h-1 to room temperature. By means of energy dispersive analysis
of emitted X-rays (CamScan CS 4DV, EDX system, Noran Instruments;
30 kV, Zr-L, Te-L; detection limit: Be) no other elements than Zr and
Te were found.
DSC Investigations. Differential scanning calorimetry (DSC)
investigations were performed with the help of a SETARAM Setsys
16/18 with PtRh 6%/PtRh 30% thermocouples. The samples, 20-80
mg, were pressed into pellets (L 3.5 mm, 6.5 kN), and put in a
molybdenum crucible, which subsequently was sealed under an argon
atmosphere. The sample crucible, together with an empty reference
crucible, was placed on the DSC transducer. The furnace compartment
was evacuated (P < 1 Pa) and flooded with purified argon. This
procedure was repeated three times before a measurement was
conducted under a stream of purified argon. The heating rate used was
10 K min-1; cooling rates were 10-40 K min-1. No significant weight
changes of the molybdenum crucibles were detected. Reactions between
molybdenum and the specimens were not observed.
Figure 1. X-ray powder diffractogram (Cu KR, relative intensities vs
2θ) and a Rietveld profile fit for ZrTe (MnP). Measured (dots) and
calculated (line) intensities with a difference plot (bottom, 50%
expanded). In the middle are shown the positions of the Bragg angles
of ZrTe (MnP).
Table 1. Selected Crystallographic Data for ZrTe (MnP)
chemical formula
fw (g mol-1
space group
Z
ZrTe
218.824
orthorhombic, Pnma (No. 62)
4
)
a (pm)
b (pm)
739.15(15)
377.23(8)
694.34(14)
193.60(7)
7.507
19.90
0.0212; 0.0215
0.0519
The calibration of the DSC transducer was achieved with the
measurement of the temperature and heat of fusion of Au (ca. 10 mg;
99.99%, SETARAM) in open Mo crucibles. Au melts at 1337 K,
c (pm)
V (106 pm3)
F
calcd (g cm-3
)
∆
fusH01337 ) 12.55 kJ mol-1 19
. Only the heating peaks of the DSC
µ (mm-1
)
experiments were used for evaluation, both in calibration measurements
and in sample measurements.
R(Fo)a (Io > 2σ(Io)); R(Fo)
2
Rw(Fo )b
Powder X-ray Diffraction. Guinier X-ray powder diffraction was
used as a characterization method for phase identification. Guinier
photographs were obtained with a Huber Guinier System 600 employing
Cu KR1 radiation. Silicon20 was added to the samples as an internal
standard. Lattice parameters were determined from Guinier diffraction
data by least-squares refinement with use of the local program
DIFFRAKT.21 X-ray powder diffractograms were recorded in reflection
at ambient temperature on a Philips X’Pert MPD diffractometer with
Bragg-Brentano geometry, equipped with a diffracted-beam curved
graphite monochromator, using Cu KR radiation (40 kV, 40 mA).
Intensities were detected by means of a scintillation counter. An X-ray
powder diffraction pattern and a Rietveld profile fit for a ZrTe (MnP)
sample are shown in Figure 1.
goodness of fit
1.208
a R(Fo) ) ∑||Fo| - |Fc||/∑|Fo|. b w ) 1/[σ2(Fo ) + (0.0294P)2 +
2
0.5079P]; P ) (Fo + 2Fc2)/3.
2
The lattice parameters determined for the single crystal on the basis of
the positions of 3024 reflections and those from Guinier powder
diffraction data (38 reflections, a ) 738.09(8) pm, b ) 376.92(3) pm,
c ) 694.09(8) pm) are in fair agreement. No signs of a partial
occupation of the atomic sites were found.
Electrical Resistivity Measurements. The temperature dependence
of the electrical resistivity of ZrTe (MnP) was determined between 10
and 300 K on a cold-pressed powder sample (13.0 × 2.0 × 1.25; length
× width × thickness, mm) applying a four-probe dc method.24 The
sample was fixed on a mica plate which in turn was brought onto a
copper plate to ensure good thermal contact with the coldfinger of the
apparature. Contact wires of gold were attached to the sample with a
silver paste. To compensate for errors due to thermal stress, the
resistivity was measured by using both current directions (I ) 8 mA).
To check for hysteresis effects, the resistivity was measured upon
cooling as well as upon heating.
Magnetic Susceptibility Measurements. Magnetic susceptibility
measurements were carried out with the aid of a Quantum Design
MPMS SQUID magnetometer with a He cryostat. The data were
corrected for diamagnetism of sample holders and atom cores.25
Powdered samples of 100-200 mg of ZrTe (MnP) were loaded into
polytetrafluorethylene (KLF) sample holders in an Ar-filled glovebox.
Magnetization measurements were carried out between 1.8 and 330 K
in fields of 10 and 30 kG. The field dependence of the magnetization
was measured at 5 K.
Single-Crystal X-ray Diffraction. The selected, rectangularly
shaped crystals with a silver luster were mounted in argon-filled glass
capillaries. A data set of a suitable crystal was collected on an IPDS
diffractometer (Stoe) at room temperature. Data reduction was per-
formed with the IPDS-software, X-RED and X-SHAPE.22 The structure
was refined by using the program SHELXL-97.23 Selected data for the
single-crystal X-ray structure investigation of ZrTe (MnP) are given
in Table 1. Positional parameters and isotropic, equivalent temperature
factors, as well as anisotropic temperature factors, are given in Table
2. Selected interatomic distances may be found in Table 3. A numerical
absorption correction resulted in a significant improvement of the final
2
residual factors (before correction: R(Fo) ) 0.0248; Rw(Fo ) ) 0.0629).
(19) Lide, D. R., Ed. CRC Handbook of Chemistry and Physics, 76th
ed.; CRC Press: Boca Raton, FL, 1996.
(20) Deslattes, R. D.; Henins, A. Phys. ReV. Lett. 1976, 36, 898.
(21) Wagner, V.; Degen, T. DIFFRAKT (V1.0), a program for processing
X-ray powder data; Universita¨t Bonn, 1995.
(22) STOE & Cie: X-RED 1.07, Data reduction for STADI4 and IPDS;
X-SHAPE 1.01, Crystal optimisation for numerical absorption correction;
Darmstadt, 1996.
(23) Sheldrick, G. M. SHELXL-97, Program for the refinement of crystal
structures; Universita¨t Go¨ttingen, 1997.
(24) Crawford Dunlap, W., Jr. In Methods of experimental physics, Vol.
6, Part B: Solid-state physics; Horovitz, K. L., Johnson, V. A., Eds.;
Academic Press: New York, 1959; p 33.
(25) Weiss, A.; Witte, H. Magnetochemie; VCH: Weinheim, 1973; p
95.

4170 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
O¨ rlygsson and Harbrecht
Table 2. Atomic Coordinates and Equivalent (Ueq) and Anisotropic Displacement Parameters for ZrTe (MnP) (in pm2)
atom
site
x
y
z
Ueq
U11
U22
U33
U23
U13
U12
Te1
Zr1
4c
4c
0.70906(5)
0.00829(7)
1/4
1/4
0.42623(4)
0.69123(7)
38.7(16)
45.3(17)
44(2)
43(3)
38(2)
59(3)
34(2)
33(3)
0
0
-5.7(10)
0.6(15)
0
0
Table 3. Selected Interatomic Distances (in pm)
Zr1-Te1
Zr1-Te1
Zr1-Te1
Zr1-Te1
Zr1-Zr1
Zr1-Zr1
Zr1-Zr1
1×
2×
2×
1×
2×
2×
2×
287.71(7)
293.05(6)
296.66(6)
304.26(8)
325.95(7)
377.23(8)
378.5(1)
Te1-Zr1
Te1-Zr1
Te1-Zr1
Te1-Zr1
Te1-Te1
Te1-Te1
Te1-Te1
1×
2×
2×
1×
2×
2×
4×
287.71(7)
293.05(6)
296.66(6)
304.26(8)
376.28(7)
377.23(8)
399.71(7)
Table 4. Parameters Used for Extended Hu¨ckel Calculations for
ZrTe (MnP)
a
b
a
b
orbital
Zr
Hii (eV)
ú1
c1
ú2
c2
5s
5p
4d
5s
5p
-7.942
-4.353
-7.756
-21.20
-12.00
1.82
1.78
3.84
2.51
2.16
0.6213
1.505
0.5798
Figure 2. DSC recording of the phase transition ZrTe (WC)-ZrTe
(MnP) at 1165 °C. Two heating cycles up to 1225 °C are shown. The
endothermic enthalpy effect of the transition is clearly visible in the
heating segments. During cooling, an exothermic effect of a reverse
transition is not observed. Holding the temperature at 1000 °C for 1 h
affords a complete reverse transition; both peaks are of equivalent area.
The phase transition can be performed repeatedly on the same sample.
Note that the heat flow changes abruptly upon changes in heating rate
Te
a Slater-type orbital exponents. b Coefficients used in double-ú
expansion.
Electronic Structure Calculations. Band structure calculations on
ZrTe (MnP) were carried out within the tight-binding approximation,
at 96 k points, using the extended Hu¨ckel method.26-28 Valence-state
ionization energies (Hii’s) for Zr were obtained from charge-iterative
calculations on ZrTe (MnP), using fixed valence-state ionization
energies for Te. Other parameters were taken from the literature.29 The
parameters are listed in Table 4.
(switching effect). Heating and cooling rates were 10 °C min-1
.
As an examination of the interatomic distances as well as a
bonding analysis show (see below), formally one out of three
Zr-Zr bonds in the hexagonal plane of ZrTe (WC) has to be
broken in the course of the phase transition ZrTe (WC)-ZrTe
(MnP). One further Zr-Zr bond, as well as the total Zr-Te
interactions must be weakened. On the opposite side, due to
the zigzag chain formation, the third Zr-Zr bond gains
considerably in strength. Thus, in the first approximation, the
measured endothermic enthalpy effect could be understood as
the difference between the mentioned loss and gain terms. This
is maintained without the intention of explaining or elucidating
the transition mechanism in any way.
Results and Discussion
Phase Relations, Phase Transition. The lattice parameters
determined for ZrTe (MnP) prepared and treated with different
methods did not point to a homogeneity range. In equiatomic
samples prepared in an arc-melting furnace, diffuse reflections
of ZrTe (MnP) were observed in addition to reflections of Zr5-
Te6 and Zr5Te4.17,30 This points to the emergence of ZrTe
14
(MnP) during the cooling process. An access of ZrTe (MnP) to
the melt is considered very unlikely. Differential scanning
calorimetry (DSC) experiments in combination with phase
analysis with X-ray powder diffraction showed a first-order
reconstructive phase transition from ZrTe (WC) to ZrTe (MnP)
at 1438 ( 5 K (1165 °C). The phase transition is reversible,
although the reverse reaction is kinetically inhibited. This is
shown in Figure 2. ZrTe (MnP) is stable up to at least 1770 K.
Zr5Te4 represents the next metal-rich phase. On the tellurium-
rich side Zr5Te6 follows ZrTe (MnP).
During our investigations, we have not been able to confirm
reports on NiAs-WC type dimorphism in ZrTe,16,33 neither have
we been able to verify the existence of a NiAs type phase in
the Zr-Te system. Apart from ZrTe, a NiAs-WC type
dimorphism has been reported in NbS, NbN, and TiS.34 Those
reports, however, have not been confirmed. NbS was described
in the Introduction.10 NbN transfers at high temperatures from
a tetragonal to a cubic, NaCl type phase.35 TiS probably
exclusively crystallizes in the NiAs type.36,37
Structure maps provide an empirical basis for predicting the
structure types adopted by various compounds.38-40 For ex-
ample, Villars has constructed a three-dimensional structural
stability diagram for AB compounds,39 plotting the difference
of Zunger’s pseudopotential radii sums, the Martynov-Batsanov
The enthalpy of the phase transition ZrTe (WC)-ZrTe (MnP)
amounts to 8.3 ( 1.0 kJ mol-1. This is somewhat larger than
the transition enthalpy of 5.2 ( 0.6 kJ per mol Zr atom, which
was determined for a phase transition in Zr5Te6 occurring at
1513 ( 5 K.31 For comparison, the enthalpy of the phase
transition R-Zr f â-Zr from hexagonal to body-centered cubic
(33) Sodeck, H.; Mikler, H.; Komarek, K. L. Monatsh. Chem. 1979, 110,
1.
at 1139 K amounts to 4.1 kJ mol-1 32
.
(34) (a) Villars, P. Pearson’s Handbook, desk ed.; American Society
for Metals: Materials Park, OH, 1997. (b) Villars, P.; Calvert, L. D.
Pearson’s Handbook of Crystallographic Data for Intermetallic Phases,
2nd ed.; American Society for Metals: Materials Park, OH, 1991.
(35) Kim, S.-J.; Franzen, H. F. J. Less-Common Metals 1988, 143, 339.
(36) Wiegers, G. A.; Jellinek, F. J. Solid State Chem. 1970, 1, 519.
(37) Onoda, M.; Wada, H. J. Less-Common Metals 1987, 132, 195.
(38) Mooser, E.; Pearson, W. B. Acta Crystallogr. 1959, 12, 1015.
(39) Villars, P. J. Less-Common Metals 1983, 92, 215.
(26) Hoffmann, R. J. Chem. Phys. 1963, 39, 1397.
(27) Whangbo, M.-H.; Hoffmann, R. J. Am. Chem. Soc. 1978, 100, 6093.
(28) Ko¨ckerling, M. Program EHMACC, adapted for use on PC by M.
Ko¨ckerling, Gesamthochschule Duisburg, 1997.
(29) Clementi, E.; Roetti, C. At. Data Nucl. Data Tables 1974, 14, 177.
(30) O¨ rlygsson, G.; Harbrecht, B. Z. Kristallogr.-NCS 1999, 214, 5.
(31) O¨ rlygsson, G. Low-valent zirconium tellurides, Ph.D. Dissertation
Thesis, Philipps-Universita¨t Marburg, 2000.
(32) Guillermet, A. F. High Temp.-High Press. 1987, 19, 119.
(40) Zunger, A. Phys. ReV. 1980, B12, 5839.

Structure, Properties, and Bonding of ZrTe
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4171
Figure 3. Central projection of the ZrTe (MnP) structure parallel to
the crystallographic a-axis. The short Zr-Zr contacts in the zigzag
chains are emphasized. For comparison, the structures of ZrTe (WC)
and hypothetical ZrTe (NiAs) are shown. The line thickness of the atoms
represents their position (height) above the plane. Unit cells are indicated
with lines.
Figure 4. Temperature dependence of the electrical resistivity of ZrTe
(MnP). I ) 8 mA. Inset: Temperature dependence of the molar
magnetic susceptibility of a powder sample of ZrTe (MnP) measured
at a field of 30 kG.
Zr bonds perpendicular to the zigzag chains (parallel to [001])
are broken. This is expressed in an elongation of the structure
in the [001] direction.
electronegativity difference, and the sum of the number of
valence electrons. In this diagram, polymorphous compounds
are expressed through an overlap of the volumes of two or three
structure types. Interestingly, the WC and MnP structure types
lie side by side, allowing for the possibility of a phase transition.
ZrTe lies near the suggested boundary surface between both
structure types. Considering the present results for the structures
adopted by ZrTe, a partial overlap of both volumes has to be
assumed. As mentioned earlier, a WC-MnP type dimorphism
is reported here for the first time.
Structural Features. ZrTe (MnP) crystallizes in the MnP
type structure5 (Figure 3). In the zigzag chains, which extend
parallel to [010], the shortest Zr-Zr distances in the structure
are found, 326.0 pm. This distance is comparable to the shortest
Zr-Zr distance in Zr5Te6 (326.4 pm).14 The second Zr-Zr
contact inside the chains amounts to 377.2 pm, almost identical
to the Zr-Zr distance in the hexagonal planes in ZrTe (WC).
The Zr-Zr distance between the zigzag chains is 468.6 pm and
corresponds approximately to the distance between the Zr7
clusters in Zr5Te6, 470.5 pm. The Zr-Zr distance “parallel” to
[100] amounts to 378.5 pm. The coordination sphere of the Zr
A further result of the relaxation of the ZrTe (WC) structure
to the ZrTe (MnP) structure is a corrugation of the Te atom
layers, with an amplitude of approximately 60 pm in the [100]
direction. This is connected to the “cleft” between the Zr atom
zigzag chains; the Te atoms shift toward and into those “clefts”.
Up to now, only one telluride crystallizing in the MnP type
has been reported. MnTe crystallizes under normal conditions
in the NiAs type. According to high-pressure X-ray powder
diffraction experiments, the MnP type structure occurs reversibly
above 24 GPa, after the appearance of an intermediate phase.41
The structure of MnTe (MnP) contains strikingly short Te-Te
distances of 316.2 pm, intermediate between the two shortest
distances in elemental Te, 283.5 and 349.5 pm.42 This could be
attributed to the formation of Te-Te bonding interactions under
pressure. Similar Te-Te distances are found for example in
ZrTe3, where bonding Te-Te interactions are observed.43,44
According to that, the high-pressure modification of MnTe
differs fundamentally from ZrTe (MnP) with regard to the
crystallographic as well as the electronic structure.
atoms can be seen as a distorted octahedral one, with dZr-Te
)
Physical Properties. As can be seen in Figure 4, the
resistivity rises with temperature, pointing to a metallic behavior
of ZrTe (MnP). For a metallic compound, however, the
287.7-304.3 pm, whereas the Te atoms are distorted trigonal
prismatically surrounded with Zr atoms. The Te-Te contacts
are g376.3 pm, pointing to van der Waals interactions.
A comparison of the lattice parameters of ZrTe (MnP) and
ZrTe (WC) elucidates the geometrical relations between both
structures. The a-lattice parameter corresponds to the doubled
c-lattice parameter of ZrTe (WC) (2 × cWC ) 772.1 pm). The
b-lattice parameter is directly comparable to the a-parameter
of ZrTe (WC) (aWC ) 377.1 pm). The c-parameter stands in a
resistivity is unusually high, F10K ) 53.5 mΩ cm and F300K
55.7 mΩ cm, compared to, e.g., the same data for Zr (F10K
)
)
0.253 × 10-3 mΩ cm; F300K ) 43.3 × 10-3 mΩ cm).19 The
resistivity of a ZrTe2 single crystal at 300 K was reported as
0.5 mΩ cm.45 In addition, the residual resistance ratio of this
metallic conducting compound is much higher than that for ZrTe
(MnP), F300K/F4K ) 7-15 (ZrTe2), compared to F300K/F10K
)
31/2-relation to the a-parameter of ZrTe (WC) (31/2 × aWC
)
1.04 (ZrTe (MnP)). Apart from real specific features regarding
the transport properties, grain boundary effects in the powder
samples could, among others, be made responsible for the high
measured resistances.
653.1 pm). One recognizes that the crystallographic a-axis is
shortened (4.3%), the b-axis stays unchanged, and the c-axis is
elongated (6.3%), as compared to the transformed lattice
dimensions of ZrTe (WC). The cell volume per formula unit
(ZrTe) increases slightly from ZrTe (WC) (47.5 × 106 pm3) to
ZrTe (MnP) (48.4 × 106 pm3). The shortening of the crystal-
lographic a-axis can be related to the shifting of the atoms away
from the rigid, trigonal prismatic AbAb-arrangement of the WC
type structure. The relaxation to the MnP type structure, which
is derived from the hexagonal close-packed arrangement of the
nonmetal atoms (A, B) in the NiAs type, AcBcAc, allows this
change to take place. Compared to ZrTe (WC) half of the Zr-
The inset in Figure 4 shows the temperature dependence of
the magnetic susceptibility of ZrTe (MnP) at 30 kG. The
(41) Mimasaka, M.; Sakamoto, I.; Murata, K.; Fujii, Y.; Onodera, A. J.
Phys. C: Solid State Phys. 1987, 20, 4689.
(42) Cherin, P.; Unger, P. Acta Crystallogr. 1967, 23, 670.
(43) Felser, C.; Finckh, E. W.; Kleinke, H.; Rocker, F.; Tremel, W. J.
Mater. Chem. 1998, 8, 1787.
(44) Sto¨we, K.; Wagner, F. R. J. Solid State Chem. 1998, 138, 160.
(45) Aoki, Y.; Sambongi, T.; Levy, F.; Berger, H. J. Phys. Soc. Jpn.
1996, 65, 2590.

4172 J. Am. Chem. Soc., Vol. 123, No. 18, 2001
O¨ rlygsson and Harbrecht
observed, essentially temperature independent paramagnetic
susceptibility (ømol ) 0.14 × 10-3 cm3 mol-1) is typical for
materials with metallic transport properties resulting from
unpaired conduction electrons. A field-independent susceptibility
was obtained at 5 K.
Chemical Bonding in MnP, NiAs, and WC Type ZrTe:
A Comparison. In AB carbides and nitrides of the transition
metals, the WC type structure is adopted for valence-electron
counts of 10 per formula unit.1 Examples are WC and TaN (W
and Ta d2). In AB phosphides the NiAs type structure is
dominant for 9 and 10 valence electrons per formula unit,
whereas for 11-14 valence electrons the MnP type structure is
observed.2 An example is MoP (11 valence electrons, d3). ZrTe
contains 10 valence electrons per formula unit and can,
accordingly, be expected to adopt the WC type structure.
Bearing in mind the structures adopted by the phosphides, one
could have expected a transition to a NiAs type phase at higher
temperatures. Apparently, with the possibility of stabilization
through the formation of metal atom zigzag chains, this
alternative becomes superfluous. The gain in bonding energy
upon the emergence of the zigzag chains is seemingly preferred
to the intuitively expected increase (at least retention) of
symmetry on moving from the low- to high-temperature phase,
which would have been achieved with the formation of ZrTe
(NiAs).
The influence of the d-electron count on clustering in
chalcogenides of the valence electron poor transition metals,46
including some zirconium tellurides, has been discussed else-
where.14 The arrangement of the metal atoms to zigzag chains
is typical for phases with a d2 metal atom electron configuration.
ZrTe counts to those phases. Other representatives are for
example R- and â-ZrI2,47,48 and â-MoTe2.49 To learn more about
the factors influencing the adopted structure type, in the
following, the results of extended Hu¨ckel calculations on MnP,
NiAs, and WC type ZrTe are compared.
According to the total density of states (DOS) for ZrTe (MnP)
shown in Figure 5a, the Fermi level (ꢀF) lies in a region that is
governed by Zr d-orbital contributions. This is in accordance
with the observed metallic behavior. The Te p-orbital contribu-
tions extend downward from about 2.5 eV below ꢀF. Comparing
the DOS for ZrTe (MnP) and the undistorted, hypothetical ZrTe
(NiAs) (Figure 5b)18 clearly shows the advantages of the MnP
type structure. Zr d-electron density is shifted to lower energies,
the ꢀF lying close to a local DOS minimum. As compared to
the DOS for the low-temperature hexagonal form, ZrTe (WC)
(Figure 5c),18 the d-block of ZrTe (MnP) also is shifted slightly
to lower energies. Thus, in the high-temperature orthorhombic
form, ZrTe (MnP), there are significantly more Zr d-states
available for homonuclear bonding interactions than in both
ZrTe (WC) and ZrTe (NiAs).
Figure 5d shows the COOP diagrams for homonuclear Zr-
Zr interactions as well as heteronuclear Zr-Te interactions in
ZrTe (MnP). On the basis of the COOP diagrams it can be seen
that the heteronuclear interactions make up the main component
of the bonding interactions. In Figure 5e, a projection of the
COOP curve for the short distance in the zigzag Zr atom chain
is shown. It becomes apparent that here the main part of the
bonding Zr-Zr interactions is to be found. An analysis of the
Mulliken overlap populations (MOP) in a structure allows a
relative quantification of the bonding interactions. Table 5 shows
the MOP values for ZrTe (MnP). Corresponding values for ZrTe
Figure 5. Densities of states (DOS) (a-c) and crystal orbital overlap
population (COOP) curves (d-e). Levels up to the Fermi level (ꢀF,
broken, horizontal line) are filled; levels to the right of the vertical
line in the COOP curves are bonding, those to the left are antibonding.
(a) DOS for ZrTe (MnP), ꢀF ) -7.7 eV. (b) DOS for ZrTe (NiAs), ꢀF
) -7.0 eV. (c) DOS for ZrTe (WC), ꢀF ) -7.5 eV. (d) COOP curves
for ZrTe (MnP). COOP curves for Zr-Te and Zr-Zr contacts up to
305 and 379 pm, respectively, are shown. (e) The projected COOP
curve for the short contact (325.95 pm) in the Zr atom zigzag chain of
ZrTe (MnP).
Table 5. Interatomic Distances and Mulliken Overlap Populations
(MOP) for ZrTe (MnP)
ZrTe (MnP)
d (pm)
MOP
MOP per “bond”
Zr-Te
4×
8×
8×
4×
4×
4×
4×
287.71
293.05
296.66
304.26
325.95
377.23
378.5
1.444
2.843
2.769
1.333
1.092
0.282
0.215
0.361
0.355
0.346
0.333
0.273
0.071
0.054
Zr-Te
Zr-Te
Zr-Te
Zr-Zr zigzag
Zr-Zr parallel b
Zr-Zr parallel a
Zr-Te total/4 ) 2.097a
Zr-Zr total/4 ) 0.397b
a For ZrTe (WC): 2.152. For ZrTe (NiAs): 2.280.18 b For ZrTe
(WC): 0.355. For ZrTe (NiAs): 0.233.18
(NiAs) and ZrTe (WC) have been reported.18 Here the impor-
tance of the bonds in the zigzag chain as compared to other
Zr-Zr interactions again becomes clear. The MOP value of the
short contacts in the zigzag chain amounts to 0.273 as opposed
to 0.071 and 0.054 for the other two bonding interactions. An
examination of the MOP value for the second contact inside
the zigzag chain (0.071; 377.2 pm) is interesting. Retaining the
(46) Rouxel, J. Chem. Eur. J. 1996, 2, 1053.
(47) Guthrie, D. H.; Corbett, J. D. J. Solid State Chem. 1981, 37, 256.
(48) Corbett, J. D.; Guthrie, D. H. Inorg. Chem. 1982, 21, 1747.
(49) Brown, B. E. Acta Crystallogr. 1966, 20, 268.

Structure, Properties, and Bonding of ZrTe
J. Am. Chem. Soc., Vol. 123, No. 18, 2001 4173
same distance, this interaction turns out to be noticeably weaker
than the one in ZrTe (WC) (0.103; 377.1 pm).18 A comparison
of the integral MOP values for ZrTe (WC) and ZrTe (MnP)
shows a distinct strengthening of the homonuclear Zr-Zr bonds
in ZrTe (MnP) as opposed to ZrTe (WC) (0.355 vs 0.397). The
heteronuclear bonds become somewhat weaker (2.152 vs 2.097).
No covalent bonding nonmetal-nonmetal interactions could
be established for ZrTe (MnP) (-0.02 e MOP/atom pair e 0).
In this respect ZrTe (MnP) differs from phosphides and
arsenides exhibiting this structure type.2
An examination of the MOP values, in context with the DOS
diagrams in Figure 5, for hypothetical ZrTe (NiAs) as compared
to ZrTe (WC) and ZrTe (MnP) underlines the importance of
the bonding interactions occurring in the vicinity of the Fermi
level: Despite the dominance of heteronuclear interactions in
the total bonding interactions in all three phases, the small
variations in homonuclear interactions just below the Fermi level
are decisive as to which structure is formed. As mentioned, we
have not been able to verify the existence of a NiAs type
ZrTe.16,33
from ZrTe (WC) to ZrTe (MnP) occurs at 1438 K and is of
first order. The transition proceeds reversibly, but is kinetically
inhibited. A WC-MnP type phase transition has not been
reported before. ZrTe (MnP) shows the properties of a poor
metallic conductor with an almost temperature independent
paramagnetic susceptibility. As compared to ZrTe (WC),
extended Hu¨ckel calculations reveal a distinct increase in
bonding Zr-Zr interactions. This is attributed to the strong
contacts in the Zr atom zigzag chains and is understood as the
driving force of the transition. Metal atom zigzag chains are
observed in pnictides, chalcogenides, and halides of valence
electron poor transition metals in which a d2 electron config-
uration is realized. This is also the case in ZrTe.
Acknowledgment. Financial support by the Deutsche For-
schungsgemeinschaft and the Fonds der Chemischen Industrie
is gratefully acknowledged. We would like to thank Mr. Ru¨diger
Penzel for assistance with the DSC measurements.
Supporting Information Available: A table of additional
crystallographic and refinement data and tables of relevant
parameters of the Rietveld analysis with a listing of 2θ values,
indexation, and calculated and observed relative X-ray diffrac-
tion intensities (PDF) and an X-ray crystallographic file (CIF).
This material is available free of charge via the Internet at
http://pubs.acs.org.
Conclusions
At equiatomic composition in the system Zr-Te a new high-
temperature phase was uncovered. ZrTe crystallizes in a
distorted NiAs type structure of the MnP type, in which the Zr
atoms are arranged to zigzag chains. The low-temperature phase
crystallizes in the WC type. The reconstructive phase transition
JA004164R