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Synthesis and crystal structure of Zr3Te
Journal of
AN[} CO~FOUNDS ELSEVIER
Journal of Alloys and Compounds 238 (1996) 13-17
Synthesis and crystal structure of Zr3Te 1 B. Harbrecht, R. Leersch lnstitut f iir Anorganische Chemie, Universitiit Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany Received 11 August 1995
Abstract Zr3Te was prepared by arc-melting a compressed mixture of ZrTe 2 and zirconium and annealing of the sample at 1650 K in a sealed tantalum ampoule. The structure was determined by means of X-ray powder diffractometry and confirmed by a single-crystal structure analysis: a = 1132.7(1) pm, c = 563.64(7) pro, I - 4, Z = 4, t132, 1638 reflections, 38 variables, R F = 0.022. Zr3Te adopts a Ni3P-type structure. The structure comprises tetrakaidecahedral ZrgTe clusters sharing two faces, five edges and four vertices with other units of the same type. The specific orientation of the clusters affords a structure in which nearly all atoms aie tetrahedrally close-packed. Keyword~: Transition metal tellurides; Crystal structure; High temperature synthesis
1. Introduction Although several zirconium-rich tellurides have been mentioned in the literature [1-6], only ZrsTe 4 [4,5] (TisTe 4 [7] structure type) has been identified beyond all doubt. Compositions of other phases were corrected later on: 'ZraTe3', for example, turned out to be a ternary silicide, ZrSiTe [8]. The existence of a binary telluride of a Be3Nb-type structure [9] has to be quesr, ioned because the density calculated from the reported data [6] exceeds the value estimated by volume increments by a factor of about 1.4. In the course of a reinvestigation of the phase relations in the metal-rich region of the Z r - T e system we uncovered at least two new binaries. Zr3Te , the most zirconiumrich intermediate phase, is the subject of this report. Its structure is related to that of the high temperature modification of V3S [10].
2. Preparation Preparative investigations in the Z r - T e system were performed in the region 0.56
0925-8388/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0925 -8388( 95 ) 0 2 0 7 8 - 0
quartz glass ampoules (1150 K, 1 day). ZrTe 2 and zirconium were mixed, cold-pressed and arc-melted on a water-cooled copper plate in a flow of argon (1.05 × 105 Pa, 50 cm 3 s-l). A tungsten tip was used as a second non-consumable electrode. Mass loss due to vaporization of tellurium could be restrained to 0.51.5% by optimizing the power. Selected samples were subsequently annealed in sealed tantalum tubes (15501650 K, 12-72 h). Air-sensitive ZrTe 2 and ZrsTe 4 samples were handled in a glove box and stored under argon.
3. Phase analyses and structure determination All samples were examined by means of X-ray powder diffractometry. Guinier photographs (FR552, Enraf Nonius) were made with use of Cu Ka~ radiation. Silicon was admixed to the samples as an internal standard [11 ]. The diffraction pattern of the telluride so far richest in zirconium could be indexed on the basis of a tetragonal body centred lattice which is related to that of ht-V3S [10]. The results are given in Table 1. Energy dispersive analysis (EDX; PV 9800, Edax) of such a sample mounted in a scanning electron microscope (SEM; DSM 940, Zeiss) confirmed the composition: Zr0.76(3)Te0.2~. Within the accuracy of the E D X method a contamination of the material by silicon or tantalum can be excluded.
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
14
Table 1 X-ray diffraction of Zr3Te (Cu Kay, sin20 < 0.2)
hkl
110 101 220 211 310 400 002 321 330 112 420 202 411 222 510 312 431 501 402 521 530 332 422 103 620 611 213 512
sin20 × 105
Ir~"
Calc.
Obs.
Calc.
Obs.
924 2336 3696 4184 4620 7392 7497 7880 8316 8421 9240 9245 9728 11193 12012 12117 13424 13424 14888 15272 15708 15812 16736 17329 18480 18968 19177 19508
922 2333 3697 4188 4620 7399 7496 7875 8312 8421 9233 9346 9723 11197 12009 12109 13425 13425 14893 15274 15707 15808 16742 17329 18473 18969 19182 19506
27 14 44 98, 16 h 18, l 16 5 237,211 296 344 240 128 371,239 323 220, 2 208, 1 100, 4 28 63 44, 27 26, 5 61 31, 6 28 23, 0 53, 21 7, 1 20, 3
29 14 45 98. 16 19, 1 16 5 236,211 283 333 228 118 367, 237 338 214, 2 205, 1 101, 4 29 64 45, 27 26. 5 60 33, 6 30 24, 0 55, 21 8, 1 22, 3
" Rel. intensities as obtained from Rietveld analysis. l~,k~ and lk~. values which differ by symmetry.
The X-ray diffractogram (PW 1050, Philips, Cu Ko0 of a sample which contained zirconium as a minor component was taken in the range 10°<20 <110 ° (step width: 0.03°; exposure time: 45 s per step). Intensity calculations on the basis of the structural parameters of ht-V3S [10] led to a pattern bearing a strong resemblance to the observed one. Rietveld refinements [12] of this model structure converged at a residual profile value R e =0.083 when intensity contributions by the elemental metal were taken into account. A significantly better fit (Re =0.035) was obtained after releasing the coupling of the x- and y-parameters resulting in a Ni3P-type structure [13,14] of low Laue symmetry. The Rietveld profile fit is shown in Fig. 1. The positional parameters are compared with single crystal data in Table 2. The accuracy of the positional parameters derived by profile fitting may, owing to low Laue symmetry ( I - 4), suffer from the perfect superposition of symmetry independent reflections. Therefore, attempts were made to isolate a crystal of suitable quality for a precise structure determination. A grain of irregular shape (0.18×0.08×0.07 mm 3) was found to be a single crystal. Weissenberg photographs (Ni-filtered Cu
i
, ,
.........
,,,--,
v,,,F
......
, ......
t..l__ L -,-i,•
r
.
~, ..... ,, ,F,,~,-,~,,,~,,-,~
1. . . . . . .
.
.
.
L. .
.......... ,,,
.
~,
.
il ......... i .................................................................... • 20
40
60 2O
Fig. 1. Rietveld profile fit of a X-ray powder diffractogram (Cu K~) of Zr3Te and Zr~ ~.Te.,; top: measured (points) and calculated (line) intensities; bottom: difference between measured and calculated intensities; middle: position of the Bragg angles of Zr3Te and Zr~_xTe x solid solution.
K radiation) of the layers hkO and hkl clearly proved the lack of mirror planes perpendicular to, for example, a* and a* + b*. The intensity data were collected at ambient temperature using a four circle diffractometer (CAD 4, Enraf Nonius, Delft). The data processing and structure calculations were performed with the structure determination program SDP Plus (B. Frenz, Enraf Nonius) implemented on a VaxStation 4000 (Digital Equipment Corporation). Further information concerning data collection and processing, absorption correction and structure calculations are given in Table 3. Anomalous dispersion effects owing to the lack of a centre of symmetry were taken into account. The data were transformed according to the setting of meteoritic rhabdite, Fe2NiP [16].
4. Results and discussion
Pure Zr3Te is not accessible from the melt; it melts incongruently. In as-cast samples with mole fraction XZr /> 0.79, Zr3Te coexists with the metal. In as-cast samples of composition 0.71 < Xzr < 0.79 a third, not yet characterized, phase is present. The synproportionation of the metal and the unknown phase is rather sluggish even at 1650 K. Coarse-crystalline Zr3Te has a silver lustre. It is brittle and, in contrast to phases richer in tellurium, stable in air. No preferential direction with respect to growth and break was found. Positional and displacement parameters are listed in Tables 3 and 4. Table 5 contains interatomic distances in the first coordination shells. Following the description of the Ni3P-type structures given by Hyde and Andersson [17], Zr3Te is composed of Z r 4 tetrahedra which are trans-edge-
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
15
Table 2 Positional parameters and displacement parameters (104 pm 2) of Zr3Te (first row: single crystal data; second row: Rietveld data) Atom
Position
x
y
z
Bcq
Zrl
8g
0.08262(4) 0.0833(6)
0.10298(3) 0.1023(6)
0.21431(7) 0.2136(12)
0.628(5) 3.07(20)
Zr2
8g
0.14154(3) 0.1413(4)
0.48023(4) 0.4801(6)
0.48031(8) 0.4819(14)
0.678(5) 2.06(15)
Zr3
8g
0.31318(3) 0.3160(5)
0.28273(4) 0.2818(5)
0.26171(8) 0.2642(13)
0.620(5) 1.84(15)
Tel
Sg
0.28879(2) 0.2905(4)
0.03174(2) 0.0305(4)
0.4780(5) 0.4727(10)
0.617(3) 2.64(1l)
Table 5
Table 3 Crystallographic data of Z3Te Formula Space group type (No.) a (pro) c (pm) V x 106 pm ~ Z P~c (g cm-~) Molar mas~ (g tool l) X-ray, monochromator Absorptior coef. /~ (cm l) Crystal size (mm 3) Scan type Min.-max. transmission [1] Measured octants, (0-region) Number of reflexions measured
Zr3Te 1 - 4 (82) 1132.7(1) 562.64(7) 721.9 8 7.384 401.26 Mo Ka, graphite 160.73 0.18 x 0.08 × 0.07 ~o-20 0.71-1.00 _+h + h _+l, ( 0 ~ 30°) 3538 1824 1638 38 0.029 0.02210.026 3.41 x 10 6 2.6
symmetr'¢-independent
/,, > 2c-(1o) Number of variables Rm,(1o > 2~-(/,,) R(F)/Rve(F ) Second extinction coefficient
Apm,~ X 10 6 (e pm -3)
Relevant interatomic distances (pm) for Zr3Te (all standard deviations are less than 0.1 pm)
Zr(1)-Te(1) -Zr(l) -Te(1) -Zr(3) -Zr(1) -Zr(2) -Zr(3) -Zr(2) -Zr(3) -Zr(3) -Zr(3) -Zr(1) Zr(3)-Te(1) -Te(1) -Zr(1) -Te(1 ) -Zr(2) -Zr(2) -Zr(3) -Zr(1) -Zr(2) -Zr(1) -Zr(1) -Zr(1)
fused into chains. One kind of chain, running parallel to c and passing the origin and centre of the cells, are built up by Zr(1). Zr(3) covers the faces of the Zr(1)4 tetrahedra, thus forming so called stellae quadrangulae. These groupings are the 'metal cores' of Zr3Te. In these locally dense-packed regions the Zr atoms c o m e closer to each other ( d [ Z r ( 1 ) - Z r ( 1 ) ] = 299.1 pm, d[Zr(1)-Zr(3)] = 309.1 pro) than in the metal (greater than 318 pm). The Zr(2) atoms form a second tetrahedral chain, likewise extending parallel to c. However, the distances Zr(2)-Zr(2) (greater than 323.8 pm)
288.3 299.l 301.6 309.1 320.8 (2x) 330.4 332.2 351.9 353.0 354.3 362.2 384.8 (2x) 287.9 293.4 309.1 310.6 318.4 320.9 324.2 (2x) 332.2 341.2 353.0 354.4 362.2
Zr(2)-Te(1) -Te(1) -Te( 1) -Te( 1) -Zr(3) -Zr(3) -Zr(2) -Zr( 1) -Zr(3) Zr(2) -Zr(l) -Zr(2) Te(1)-Zr(3) -Zr( 1) -Zr(2) -Zr(2) Zr(2) -Zr(2) Zr(1) -Zr(3)
290.6 291.5 293.4 293.5 318.4 320.9 323.8 330.4 341.2 345.8 (2 x ) 351.9 380.1 (2×) 287.9 288.3 290.6 291.5 293.4 (2x) 293.5 301.6 310.6
are indicative of weaker metal-metal bonds. The lower cohesion of the Zr(2) atoms is associated with strong heteronuclear interactions (d[Zr(2)-Te(1)] = 290.6-293.5 pm). The Te(1) atoms are situated above the faces of the Zr(2)4 tetrahedra, thus forming stellae quandrangulae together with Zr(2)4. The specific orientation of the two distinct stellae quadrangulae, Zr(1)4Zr(3)4 Zr(2)4Ye(1)a, affords a structure in which the atoms are arranged to more or
Table 4 Anisotropic displacement parameters (pm 2) of Zr3Te (single crystal data)
Atom
U11
U22
U33
UI 2
UI 3
U23
Zrl Zr2 Zr3 Tel
70(1) 73(1) 83(1) 73.6(8)
82(1) 97(1) 75(1) 88.7(8)
86(1) 87(1) 78(1) 72.1(8)
-3(1) 4(1) 14(1) 7.5(7)
-8(1) 2(1) -4(1) -2.0(8)
0(1) -6(1) 2(1) -11.5(8)
16
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
less distorted tetrahedra. In this regard the structure shows some similarities with tetrahedral close-packed structures of which the Frank-Kasper phases are the most prominent representatives [18-20]. An alternative description [13] starts with the coordination polyhedron about Te(1). This is built up by nine metal atoms, six form a trigonal prism; three more cap the rectangular faces of the prism. Thus, the coordination figure represents a convex polyhedron consisting of 14 triangular faces, a triangulated tetrakaidecahedron [21] (Fig. 2). The Te(1)-Zr distances range from 287.9-310.6 pm. The peripheral Z r - Z r distances scatter much more; except for two short contacts (d[Zr(2)-Zr(2)] = 323.8 pm) the distances are rather large between atoms in prismatic sites (351.9457.7 pm). Most of the 12 distances between atoms in capping and prismatic positions (318.4-362.2 pm), however, are in the range of attractive Z r - Z r interactions. It is noteworthy that the complete structure results from the fusion of such strongly metal-metal bonded, Te-stabilized Zr9Te clusters. Four of these tetrakaidecahedral units are fused via common faces into a complex cluster of tetrahedral shape. As seen from Fig. 3, these large clusters are condensed into columns. The columns are linked by common edges and vertices. Fig. 2 shows a projection of the structure along the direction of the columns (i.e. c axis) as a polyhedral representation (program package, DIAMOND [22]). Note that adjacent columns are shifted relative to each other by about c/2. The Te(1) surrounding the Zr9Te
Fig. 3. Polyhedral representation of a column of face- and edgeshared ZrgTe tetrakaidecahedra running along c.
II
M Fig. 4. A tetrakaidecahedral ZrgTe unit surrounded by 11 Te atoms.
Fig. 2. Projection of the structure of Zr3Te along the c axis. Note, that the stellae quadrangulae Zr(1)4Zr(3)4 are located around the squares. The stellae quadrangulae Zr(2)4Te(1)4 run through the centre of the columns formed by edge- and face-fused tetrakaidecahedra.
cluster (Fig. 4) reveals the complete pattern of the condensation of the Zr9Te units. Each cluster shares two adjacent faces, five edges and four vertices with other units of the same type. The condensed Zr9Te tetrakaidecahedra encage 'cavities', which are filled by Zr(1)4Zr(3)4 stellae quadrangulae located around the 'squares' (see Fig. 2), by chains of edge4used Zr(2)4 tetrahedra located in the centre of the columns and by
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
/
Or
/"
• ,
17
Acknowledgements \
This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie and the Ministerium fiJr Wissenschaft und Forschung des Landes Nordrhein-Wesffalen.
References
Fig. 5. Telrahedral close-packed metal atoms bonded to the ZrgTe unit with its 11 Te neighbours.
additional Zr 4 tetrahedra (formed by Zr(1), Zr(2) and Zr(3)) located in the inter-column region. Such a region of tetrahedral close-packed metal atoms surrounding a Zr,~Te polyhedron is shown in Fig. 5.
5. Conclusions (1) By applying high temperature synthesis techniques we have uncovered two additional zirconiumrich tellurides. (2) ZI3Te, the most metal-rich intermediate phase of the ,;ystem coexisting with the melt, forms in a peritectic reaction. (3) Z~3Te is the first chalcogenide adopting a Ni3Ptype sm~cture. The structural data of Zr3Te are the most accurate so far reported for this structure type.
[1] H. Hahn and E Ness, Naturwissenschaften, 44 (1957) 534. [2] F.K. McTaggert and A.D. Wadsley, Aust. J. Chem., II (1958) 445. [3] H. Hahn and E Ness, Z. Anorg. Allg. Chem.. 302 (1959) 136. [4] L. Brattas and A. Kjekshus, Acta. Chem. Scand., 25 (1971) 2350. [5] H. Sodeck, H. Mikler and K.L. Komarek, Monatsh. Chem., 110 (1979) 1. [6] T. Matkovic, M. Kesic-Racan and E Matkovic, J. Less-Common Met.. 138 (1988) L1. [7] F. Gronvold, A. Kjekshus and F. Raaum, Acta Crystallogr., 14 (1961) 930. [8] H. Onken, K. Vierhellig and H. Hahn, Z. Anorg. Allg. Chem., 333 (1964) 267. [9] D.E. Sands, A. Zalkin and O.H. Krikorian, Acta Crystallogr., 12 (1959) 461. [10] B. Pedersen and F. Gronvold, Acta Crvstallogr., 12 (1959) 1022. [11] R.D. Deslattes and A. Henins, Phys. Rev. Lett., 36 (1976) 898. [12] D.B. Wiles and R.A. Young, J. Appl. Crystallogr., 10 (1977) 354. [13] B. Aronsson, Acta Chem. Scand., 9 (1955) 137. [14] S. Rundquist, E. Hassler and L. Lundvik, Acta Chem. Scand. 16 (1962) 242. [15] N. Walker and D. Stuart, Acta Crystallogr. Sect. A. 39 (1983) 158. [16] F. Doenitz, Z. Kristallogr., 131 (1970) 222. [17] B.G. Hyde and S. Andersson, Inorganic Crystal Structures, Wiley, 1988. [18] F.C. Frank and J.S. Kasper, Acta Crystallogr., 11 (1958) 184. [19] F.C. Frank and J.S. Kasper, Acta Crystallogr., 12 (1959) 483. [20] D.E Shoemaker and C.B. Shoemaker, Acta Crystallogr. Sect. B, 42 (1986) 3. [21] B. Aronsson and S. Rundquist, Acta Crystallogr., 15 (1962) 878. [22] K. Brandenburg and G. Bergerhoff, D~AMOND,1995 (Institut fiir Anorganische Cbemie der Universit~it Bonn).
AN[} CO~FOUNDS ELSEVIER
Journal of Alloys and Compounds 238 (1996) 13-17
Synthesis and crystal structure of Zr3Te 1 B. Harbrecht, R. Leersch lnstitut f iir Anorganische Chemie, Universitiit Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany Received 11 August 1995
Abstract Zr3Te was prepared by arc-melting a compressed mixture of ZrTe 2 and zirconium and annealing of the sample at 1650 K in a sealed tantalum ampoule. The structure was determined by means of X-ray powder diffractometry and confirmed by a single-crystal structure analysis: a = 1132.7(1) pm, c = 563.64(7) pro, I - 4, Z = 4, t132, 1638 reflections, 38 variables, R F = 0.022. Zr3Te adopts a Ni3P-type structure. The structure comprises tetrakaidecahedral ZrgTe clusters sharing two faces, five edges and four vertices with other units of the same type. The specific orientation of the clusters affords a structure in which nearly all atoms aie tetrahedrally close-packed. Keyword~: Transition metal tellurides; Crystal structure; High temperature synthesis
1. Introduction Although several zirconium-rich tellurides have been mentioned in the literature [1-6], only ZrsTe 4 [4,5] (TisTe 4 [7] structure type) has been identified beyond all doubt. Compositions of other phases were corrected later on: 'ZraTe3', for example, turned out to be a ternary silicide, ZrSiTe [8]. The existence of a binary telluride of a Be3Nb-type structure [9] has to be quesr, ioned because the density calculated from the reported data [6] exceeds the value estimated by volume increments by a factor of about 1.4. In the course of a reinvestigation of the phase relations in the metal-rich region of the Z r - T e system we uncovered at least two new binaries. Zr3Te , the most zirconiumrich intermediate phase, is the subject of this report. Its structure is related to that of the high temperature modification of V3S [10].
2. Preparation Preparative investigations in the Z r - T e system were performed in the region 0.56
0925-8388/96/$15.00 © 1996 Elsevier Science S.A. All rights reserved SSDI 0925 -8388( 95 ) 0 2 0 7 8 - 0
quartz glass ampoules (1150 K, 1 day). ZrTe 2 and zirconium were mixed, cold-pressed and arc-melted on a water-cooled copper plate in a flow of argon (1.05 × 105 Pa, 50 cm 3 s-l). A tungsten tip was used as a second non-consumable electrode. Mass loss due to vaporization of tellurium could be restrained to 0.51.5% by optimizing the power. Selected samples were subsequently annealed in sealed tantalum tubes (15501650 K, 12-72 h). Air-sensitive ZrTe 2 and ZrsTe 4 samples were handled in a glove box and stored under argon.
3. Phase analyses and structure determination All samples were examined by means of X-ray powder diffractometry. Guinier photographs (FR552, Enraf Nonius) were made with use of Cu Ka~ radiation. Silicon was admixed to the samples as an internal standard [11 ]. The diffraction pattern of the telluride so far richest in zirconium could be indexed on the basis of a tetragonal body centred lattice which is related to that of ht-V3S [10]. The results are given in Table 1. Energy dispersive analysis (EDX; PV 9800, Edax) of such a sample mounted in a scanning electron microscope (SEM; DSM 940, Zeiss) confirmed the composition: Zr0.76(3)Te0.2~. Within the accuracy of the E D X method a contamination of the material by silicon or tantalum can be excluded.
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
14
Table 1 X-ray diffraction of Zr3Te (Cu Kay, sin20 < 0.2)
hkl
110 101 220 211 310 400 002 321 330 112 420 202 411 222 510 312 431 501 402 521 530 332 422 103 620 611 213 512
sin20 × 105
Ir~"
Calc.
Obs.
Calc.
Obs.
924 2336 3696 4184 4620 7392 7497 7880 8316 8421 9240 9245 9728 11193 12012 12117 13424 13424 14888 15272 15708 15812 16736 17329 18480 18968 19177 19508
922 2333 3697 4188 4620 7399 7496 7875 8312 8421 9233 9346 9723 11197 12009 12109 13425 13425 14893 15274 15707 15808 16742 17329 18473 18969 19182 19506
27 14 44 98, 16 h 18, l 16 5 237,211 296 344 240 128 371,239 323 220, 2 208, 1 100, 4 28 63 44, 27 26, 5 61 31, 6 28 23, 0 53, 21 7, 1 20, 3
29 14 45 98. 16 19, 1 16 5 236,211 283 333 228 118 367, 237 338 214, 2 205, 1 101, 4 29 64 45, 27 26. 5 60 33, 6 30 24, 0 55, 21 8, 1 22, 3
" Rel. intensities as obtained from Rietveld analysis. l~,k~ and lk~. values which differ by symmetry.
The X-ray diffractogram (PW 1050, Philips, Cu Ko0 of a sample which contained zirconium as a minor component was taken in the range 10°<20 <110 ° (step width: 0.03°; exposure time: 45 s per step). Intensity calculations on the basis of the structural parameters of ht-V3S [10] led to a pattern bearing a strong resemblance to the observed one. Rietveld refinements [12] of this model structure converged at a residual profile value R e =0.083 when intensity contributions by the elemental metal were taken into account. A significantly better fit (Re =0.035) was obtained after releasing the coupling of the x- and y-parameters resulting in a Ni3P-type structure [13,14] of low Laue symmetry. The Rietveld profile fit is shown in Fig. 1. The positional parameters are compared with single crystal data in Table 2. The accuracy of the positional parameters derived by profile fitting may, owing to low Laue symmetry ( I - 4), suffer from the perfect superposition of symmetry independent reflections. Therefore, attempts were made to isolate a crystal of suitable quality for a precise structure determination. A grain of irregular shape (0.18×0.08×0.07 mm 3) was found to be a single crystal. Weissenberg photographs (Ni-filtered Cu
i
, ,
.........
,,,--,
v,,,F
......
, ......
t..l__ L -,-i,•
r
.
~, ..... ,, ,F,,~,-,~,,,~,,-,~
1. . . . . . .
.
.
.
L. .
.......... ,,,
.
~,
.
il ......... i .................................................................... • 20
40
60 2O
Fig. 1. Rietveld profile fit of a X-ray powder diffractogram (Cu K~) of Zr3Te and Zr~ ~.Te.,; top: measured (points) and calculated (line) intensities; bottom: difference between measured and calculated intensities; middle: position of the Bragg angles of Zr3Te and Zr~_xTe x solid solution.
K radiation) of the layers hkO and hkl clearly proved the lack of mirror planes perpendicular to, for example, a* and a* + b*. The intensity data were collected at ambient temperature using a four circle diffractometer (CAD 4, Enraf Nonius, Delft). The data processing and structure calculations were performed with the structure determination program SDP Plus (B. Frenz, Enraf Nonius) implemented on a VaxStation 4000 (Digital Equipment Corporation). Further information concerning data collection and processing, absorption correction and structure calculations are given in Table 3. Anomalous dispersion effects owing to the lack of a centre of symmetry were taken into account. The data were transformed according to the setting of meteoritic rhabdite, Fe2NiP [16].
4. Results and discussion
Pure Zr3Te is not accessible from the melt; it melts incongruently. In as-cast samples with mole fraction XZr /> 0.79, Zr3Te coexists with the metal. In as-cast samples of composition 0.71 < Xzr < 0.79 a third, not yet characterized, phase is present. The synproportionation of the metal and the unknown phase is rather sluggish even at 1650 K. Coarse-crystalline Zr3Te has a silver lustre. It is brittle and, in contrast to phases richer in tellurium, stable in air. No preferential direction with respect to growth and break was found. Positional and displacement parameters are listed in Tables 3 and 4. Table 5 contains interatomic distances in the first coordination shells. Following the description of the Ni3P-type structures given by Hyde and Andersson [17], Zr3Te is composed of Z r 4 tetrahedra which are trans-edge-
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
15
Table 2 Positional parameters and displacement parameters (104 pm 2) of Zr3Te (first row: single crystal data; second row: Rietveld data) Atom
Position
x
y
z
Bcq
Zrl
8g
0.08262(4) 0.0833(6)
0.10298(3) 0.1023(6)
0.21431(7) 0.2136(12)
0.628(5) 3.07(20)
Zr2
8g
0.14154(3) 0.1413(4)
0.48023(4) 0.4801(6)
0.48031(8) 0.4819(14)
0.678(5) 2.06(15)
Zr3
8g
0.31318(3) 0.3160(5)
0.28273(4) 0.2818(5)
0.26171(8) 0.2642(13)
0.620(5) 1.84(15)
Tel
Sg
0.28879(2) 0.2905(4)
0.03174(2) 0.0305(4)
0.4780(5) 0.4727(10)
0.617(3) 2.64(1l)
Table 5
Table 3 Crystallographic data of Z3Te Formula Space group type (No.) a (pro) c (pm) V x 106 pm ~ Z P~c (g cm-~) Molar mas~ (g tool l) X-ray, monochromator Absorptior coef. /~ (cm l) Crystal size (mm 3) Scan type Min.-max. transmission [1] Measured octants, (0-region) Number of reflexions measured
Zr3Te 1 - 4 (82) 1132.7(1) 562.64(7) 721.9 8 7.384 401.26 Mo Ka, graphite 160.73 0.18 x 0.08 × 0.07 ~o-20 0.71-1.00 _+h + h _+l, ( 0 ~ 30°) 3538 1824 1638 38 0.029 0.02210.026 3.41 x 10 6 2.6
symmetr'¢-independent
/,, > 2c-(1o) Number of variables Rm,(1o > 2~-(/,,) R(F)/Rve(F ) Second extinction coefficient
Apm,~ X 10 6 (e pm -3)
Relevant interatomic distances (pm) for Zr3Te (all standard deviations are less than 0.1 pm)
Zr(1)-Te(1) -Zr(l) -Te(1) -Zr(3) -Zr(1) -Zr(2) -Zr(3) -Zr(2) -Zr(3) -Zr(3) -Zr(3) -Zr(1) Zr(3)-Te(1) -Te(1) -Zr(1) -Te(1 ) -Zr(2) -Zr(2) -Zr(3) -Zr(1) -Zr(2) -Zr(1) -Zr(1) -Zr(1)
fused into chains. One kind of chain, running parallel to c and passing the origin and centre of the cells, are built up by Zr(1). Zr(3) covers the faces of the Zr(1)4 tetrahedra, thus forming so called stellae quadrangulae. These groupings are the 'metal cores' of Zr3Te. In these locally dense-packed regions the Zr atoms c o m e closer to each other ( d [ Z r ( 1 ) - Z r ( 1 ) ] = 299.1 pm, d[Zr(1)-Zr(3)] = 309.1 pro) than in the metal (greater than 318 pm). The Zr(2) atoms form a second tetrahedral chain, likewise extending parallel to c. However, the distances Zr(2)-Zr(2) (greater than 323.8 pm)
288.3 299.l 301.6 309.1 320.8 (2x) 330.4 332.2 351.9 353.0 354.3 362.2 384.8 (2x) 287.9 293.4 309.1 310.6 318.4 320.9 324.2 (2x) 332.2 341.2 353.0 354.4 362.2
Zr(2)-Te(1) -Te(1) -Te( 1) -Te( 1) -Zr(3) -Zr(3) -Zr(2) -Zr( 1) -Zr(3) Zr(2) -Zr(l) -Zr(2) Te(1)-Zr(3) -Zr( 1) -Zr(2) -Zr(2) Zr(2) -Zr(2) Zr(1) -Zr(3)
290.6 291.5 293.4 293.5 318.4 320.9 323.8 330.4 341.2 345.8 (2 x ) 351.9 380.1 (2×) 287.9 288.3 290.6 291.5 293.4 (2x) 293.5 301.6 310.6
are indicative of weaker metal-metal bonds. The lower cohesion of the Zr(2) atoms is associated with strong heteronuclear interactions (d[Zr(2)-Te(1)] = 290.6-293.5 pm). The Te(1) atoms are situated above the faces of the Zr(2)4 tetrahedra, thus forming stellae quandrangulae together with Zr(2)4. The specific orientation of the two distinct stellae quadrangulae, Zr(1)4Zr(3)4 Zr(2)4Ye(1)a, affords a structure in which the atoms are arranged to more or
Table 4 Anisotropic displacement parameters (pm 2) of Zr3Te (single crystal data)
Atom
U11
U22
U33
UI 2
UI 3
U23
Zrl Zr2 Zr3 Tel
70(1) 73(1) 83(1) 73.6(8)
82(1) 97(1) 75(1) 88.7(8)
86(1) 87(1) 78(1) 72.1(8)
-3(1) 4(1) 14(1) 7.5(7)
-8(1) 2(1) -4(1) -2.0(8)
0(1) -6(1) 2(1) -11.5(8)
16
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
less distorted tetrahedra. In this regard the structure shows some similarities with tetrahedral close-packed structures of which the Frank-Kasper phases are the most prominent representatives [18-20]. An alternative description [13] starts with the coordination polyhedron about Te(1). This is built up by nine metal atoms, six form a trigonal prism; three more cap the rectangular faces of the prism. Thus, the coordination figure represents a convex polyhedron consisting of 14 triangular faces, a triangulated tetrakaidecahedron [21] (Fig. 2). The Te(1)-Zr distances range from 287.9-310.6 pm. The peripheral Z r - Z r distances scatter much more; except for two short contacts (d[Zr(2)-Zr(2)] = 323.8 pm) the distances are rather large between atoms in prismatic sites (351.9457.7 pm). Most of the 12 distances between atoms in capping and prismatic positions (318.4-362.2 pm), however, are in the range of attractive Z r - Z r interactions. It is noteworthy that the complete structure results from the fusion of such strongly metal-metal bonded, Te-stabilized Zr9Te clusters. Four of these tetrakaidecahedral units are fused via common faces into a complex cluster of tetrahedral shape. As seen from Fig. 3, these large clusters are condensed into columns. The columns are linked by common edges and vertices. Fig. 2 shows a projection of the structure along the direction of the columns (i.e. c axis) as a polyhedral representation (program package, DIAMOND [22]). Note that adjacent columns are shifted relative to each other by about c/2. The Te(1) surrounding the Zr9Te
Fig. 3. Polyhedral representation of a column of face- and edgeshared ZrgTe tetrakaidecahedra running along c.
II
M Fig. 4. A tetrakaidecahedral ZrgTe unit surrounded by 11 Te atoms.
Fig. 2. Projection of the structure of Zr3Te along the c axis. Note, that the stellae quadrangulae Zr(1)4Zr(3)4 are located around the squares. The stellae quadrangulae Zr(2)4Te(1)4 run through the centre of the columns formed by edge- and face-fused tetrakaidecahedra.
cluster (Fig. 4) reveals the complete pattern of the condensation of the Zr9Te units. Each cluster shares two adjacent faces, five edges and four vertices with other units of the same type. The condensed Zr9Te tetrakaidecahedra encage 'cavities', which are filled by Zr(1)4Zr(3)4 stellae quadrangulae located around the 'squares' (see Fig. 2), by chains of edge4used Zr(2)4 tetrahedra located in the centre of the columns and by
B. Harbrecht, R. Leersch / Journal of Alloys and Compounds 238 (1996) 13-17
/
Or
/"
• ,
17
Acknowledgements \
This work was supported by the Deutsche Forschungsgemeinschaft, the Fonds der Chemischen Industrie and the Ministerium fiJr Wissenschaft und Forschung des Landes Nordrhein-Wesffalen.
References
Fig. 5. Telrahedral close-packed metal atoms bonded to the ZrgTe unit with its 11 Te neighbours.
additional Zr 4 tetrahedra (formed by Zr(1), Zr(2) and Zr(3)) located in the inter-column region. Such a region of tetrahedral close-packed metal atoms surrounding a Zr,~Te polyhedron is shown in Fig. 5.
5. Conclusions (1) By applying high temperature synthesis techniques we have uncovered two additional zirconiumrich tellurides. (2) ZI3Te, the most metal-rich intermediate phase of the ,;ystem coexisting with the melt, forms in a peritectic reaction. (3) Z~3Te is the first chalcogenide adopting a Ni3Ptype sm~cture. The structural data of Zr3Te are the most accurate so far reported for this structure type.
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