Preparation, structure and properties of new ternary arsenides and phosphides: Ni3Zr2P3, Ni3Zr2As3, Ni3Hf2P3 and Ni3Hf2As3

Journal of the Less-Common

Metals,

105 (1985)

187

187 - 196

PREPARATION, STRUCTURE AND PROPERTIES OF NEW TERNARY ARSENIDES AND PHOSPHIDES: Ni,Zr2P3, Ni,Zr,As,, Ni3H.f2P, AND Ni,Hf,As, E. H. EL GHADRAOUI,

J. Y. PIVAN, R. GUERIN, J. PADIOU and M. SERGENT

Laboratoire de Chimie Minirale B, Laboratoire associk au CNRS 254, Chimie du Solide et Inorganique Mole’culaire, Uniuersitk de Rennes, Campus de Beaulieu, avenue du G&&ml Leclerc, 35042 Rennes C6de.x (Fmnce) (Received

January 26,1984)

summary The compounds Ni&Xs (M = Zr, Hf; X = As, P) were synthesized. The unit cell is orthorhombic (space group, Prima) and contains four formula units. The X-ray structure of NisZr,P, was studied using three-dimensional singlecrystal counter data and was refined down to R = 0.045 for 457 independent reflections. The structure can be described as being built up of phosphorus trigonal prisms which are occupied by zirconium atoms (Zr,) and separated from each other by either [ NiP4] tetrahedra or [ ZrnP6] octahedra. This is the first time in the chemistry of arsenides and phosphides that zirconium (or hafnium) has been observed to occupy both arsenic or phosphorus octahedra and trigonal prisms. A comparative study using the structures of ZrP, and U13 is also suggested. Magnetic and electrical measurements showed almost temperature-independent paramagnetism and metallic conduction.

1. Introduction Our study of the Ni-Zr-P system enabled us to synthesize three new compounds with the formulae Ni3Zr2P3, NilZZrZP7 and Ni20Zr,$13. The only compound reported before in this system was NiZrP which has an NizIn-type structure [l]. The two compounds NilzZrzP, and Niz,,Zr6P,, are derivatives of the Cr12P,-type structure and have been described elsewhere [2]. We report here the synthesis, structural data and physical properties of the Ni3ZrzP,-type compounds since the three compounds Ni3ZrZAs3, NisHfiP3 and NisHf&+ were found to be isostructural with NisZr?Ps. 2. Preparation The compounds were prepared ent elements. The starting materials

by direct combination of the constituwere nickel and zirconium or hafnium 0 Elsevier Sequoia/Printed

in The Netherlands

188

powders ~m~irnnrn purity, 99.9%), red phosphorus (minimum purity, 99.99%) and amorphous P-As (minimum purity, 99.999%). The elements were mixed in a dry box under argon to prevent oxidation of the zirconium or hafnium, sealed under vacuum in silica tubes, annealed at 800 “C for 1 day and slowly cooled to room temperature. The samples were then ground to powder, cold pressed to small pellets, resealed and annealed for several days at 1000 “C for the phosphides and 900 “C for the arsenides. The products obtained were microcrystalline and stable in air. Well-developed ne~le-shaped crystals of NisZr,Ps were prepared by extended annealing at 1200 “c.

3. X-ray investigation Phase analysis carried out by X-ray powder methods using a proportional counter d~~ctorne~r with Cu Kor radiation showed that the four compounds NisZr,Ps, Ni,Zr,Ass, Ni&f,P, and NisHfzAss were isostructural. A single-crystal investigation of Ni3ZrzP3performed using the Weissenberg, Laue and Buerger methods (MO Key radiation) enabled the crystal lattice to be characterized as follows: orthorhombic unit cell; Laue symmetry, mmm; possible space group, Pnma or PnBra. These results agree with the systematic absences of OkE(Fz+ I = 2n + 1) and hk0 (h = 2n + 1). TABLE 1 Cell dimensions, volumes and calculated and observed densities of the Ni&P&pe pounds

com-

Compounds

a(4

b (A)

c (A)

v (A31

&cd

‘km

Ni$Zr2P3 Ni$If,PJ Ni$r&, Ni&f&~

12.297(Z) 12.199(2) 12.691(4) 12.504(6)

3.613(l) 3.608( 2) 3.726(2) 3.668( 2)

10.018(2) 9.744(3) 10.144(6) 10.032( 5)

446 429 480 460

6.74 8.77 8.08 10.07

6.60 8.67 7.93 9.92

15

10

, 25 20 Fig. 1. X-ray pattern of Ni&2P3.

50

189

The lattice constants obtained using silicon (a = 5.430 54 A) as an internal standard, the volumes and the density data (four formula units) are listed in Table 1. The X-ray pattern of Ni,Zr2P, is shown in Fig. 1.

4. Structural study of Ni,Zr,P, 4.1. Determination and refinement The intensity data for Ni3Zr2P3 were measured on an automatic fourcircle Nonius diffractometer using zirconium-filtered molybdenum radiation (h = 0.710 69 A). The conditions for the intensity measurements and the dimensions of the single crystal are listed in Table 2. TABLE 2 Crystal data for the NisZrzP3 single crystal Single-crystal dimensions Linear absorption coefficient /J Measurement limits 8 Measurement conditions Number of measured reflections Number of independent reflections Number of reflections used in refinement Z > U(Z) Final value of R Final value of R,

0.16 mm zzrn-’ h = -17, 2944 537 457

X 0.02

mm

X 0.02

mm

+17; k = 0, +5; l= -14,

+14

0.045 0.036

The structure was solved in the Puma cen~osymmet~c space group by direct methods involving calculation of the normalized structure factors E and was refined using a full-matrix least-squares program [ 31. The reliability factors R and R, , which are defined by

where K is the scale factor and o is the weight based on counting statistics, were 0.045 and 0.036 respectively after refinement of the positional and isotropic thermal parameters. A final difference synthesis showed no peaks less than -1 electron Am3or greater than 1 electron Ae3. Attempts to refine the anisotropic thermal parameters in Pnma or to solve the structure in the non-cen~osymme~c space group Pn!&a did not give s~ic~t results. The atomic and isotropic thermal coordinates are given in Table 3 and the interatomic distances are given in Table 4.

190 TABLE 3 Atomic and isotropic thermal coordinates of Ni$r,P,

ZrI ZrII Nil Nin Nim PI PU PIII

Position

x

Y

z

B(A2)

4c 4c 4c 4c 4c 4c 4c 4c

0.2087(l) 0.4961(l) 0.6667( 2) 0.2174(2) 0.4852(2) 0.6280( 3) 0.3961(3) 0.3549(3)

0.25 0.25 0.25 0.25 0.25 0.25 0.25 0.25

0.0727( 2) 0.1636( 2) 0.7264(2) 0.3643( 2) 0.5954( 2) 0.9468(4) 0.3980(4) 0.7613(4)

0.30(2) 0.23(2) 0.46(3) 0.65(4) 0.43(3) 0.26(6) 0.34(6) 0.30(6)

The standard deviations are given in parentheses. TABLE 4 Interatomic distances (in gingstriims) in Ni$r2P3 ZrI-2PI ZrI--2PU Zq-2PII Zq-2NiII Zq-Nin ZrI-PNiIII ZrI-NiI Zq-2NiI Zq-Nim ZrI-2Zq

2.708(3) 2.727(4) 2.826(3) 2.907( 2) 2.923( 3) 3.000( 2) 3.042(3) 3.108(2) 3.223(3) 3.613(l)

NiI-PI N&-P, Nil-BP11 NiI-2Nin NiI-Nim NiI-2Zrn Nil-ZrI NiI-2Zq Nil-2NiI

WI--=I

ZrII-Pn ~11-mI1

2.611(3) 2.651(4)

2.683(3)

~11-=h

2.711(4) 2.736(3) 2.912(2) 3.024( 2) 3.613(l)

2.258(4) 2.309( 5) 2.326(3) 2.475(2) 2.588(3) 2.912(2) 3.042(3) 3.108( 2) 3.613(l)

N&I-PI NiII-Pn Nin-2PIn Nin-2NiI Nin-Zrn NilI-2Zq Nin-Zq Nin-2Nin

2.188(5) 2.224(4) 2.262(3) 2.475(2) 2.736( 3) 2.907( 2) 2.923(3) 3.613(l)

Nim-Pn NiIn-Pin NiIn-2PII NinI-NiI NiIn-2Nim N&n-2ZrI N+2Zrn NinI-Zq NiIn-2Nim

2.261(5) 2.309( 5) 2.323(3) 2.588(3) 2.655(3) 3.000( 2) 3.024( 2) 3.223(3) 3.613( 1)

PI-Nin PI-NiI PI-2Zrn PI-2Zq PI-Zrn

2.188( 5) 2.258(4) 2.611(3) 2.708( 3) 2.711(4)

p1-2hI

3.444(5)

%-P1n

P1-2P1

3.481( 6) 3.613(l)

Pn-Nin PII-Nim Pn-2Nim Pn-2NiI Pn-Zrn Pn-2Zq

2.224(4) 2.261( 5) 2.323(3) 2.326(3) 2.651(4) 2.826(3) 3.613(l)

PnI-2NiII PnI-NinI PIII-Nil PnI-2Zrn Pm-2Zq

2.262(3) 2.309( 5) 2.317(5) 2.683(3) 2.727(4)

p111-2p1

3.444(5)

pII-%

ZrII-PI Zrn-NiII ZrII-2NiI ZrII-2Nim

h-P1

Pm-ZrI &II-WI1

The standard deviations are given in parentheses.

3.481(6) 3.601( 5) 3.613(l)

191

4.2. Description A projection of the crystal structure on the (010) plane is shown in Fig. 2. The structure can be viewed as being built up from alternating layers A and B of phosphorus trigonal prisms occupied by Zr, atoms; these [ZriP,] prisms are aligned along the (100) plane of the unit cell. The prisms in each

Fig. 2. Projection of the Ni$3r2P3 structure on the (010) dicate the [ ZqP,] prisms.

plane. The bold full lines in-

layer alternate (y = i and y = 4) and are separated from each other by two edge-shared phosphorus tetrahedra which are occupied by Nii and NiII atoms. Between the A and B layers the [ZrIP6] prisms are separated from each other by both [NiIIIP4] tetrahedra and [ ZrnPJ octahedra in the sequence -act-oct-tet-tetalong the [OOl] direction (all these polyhedra have common edges). Thus, for the first time in the chemistry of zirconium phosphides, the structure is characterized by two different phosphorus coordinations for the zirconium, either trigonal prisms as previously reported in ZrPz with PbCl*type structure [4] or octahedra as in cy-ZrP with rock-salt-type structure [5] or &ZrP with Tip-type structure [6]. Moreover, all the nickel atoms occupy phosphorus tetrahedra in the structure as partly found in Ni,P [ 71. If we consider the interatomic distances, we notice that the average Zr-P distance (2.658 A) in the octahedral coordination (2.64 A in CY-or p-ZrP) is less than that observed in the prismatic coordination (2.754 A (2.73 A in ZrP,)). The average Ni-P distances vary between 2.234 A and 2.305 A and are in good agreement with those in Ni2P (2.237 A). The phosphorus atoms are all isolated from each other so that no P-P bond exists in the structure.

!A

IE

(b)

(cl Fig. 3. Comparison of structures: (a) ZrPz; (b) UI,; (c) distorted UI3 after rotation of the B prisms (180 “). The structure of NiGrzP3 is shown in Fig. 2.

193

4.3. Discussion of the structure The structure of Ni,ZrzPs can be compared with that of ZrP, in which similar A and B layers of alternate [ZrP,] prisms exist (Fig. 3(a)). However, in ZrP, the prisms have a common edge between the A and B layers and are separated from each other in the same layer by two unoccupied phosphorus tetrahedral sites. Since zirconium occupies phosphorus octahedra in (Y-and /3-ZrP, we can imagine a binary Zr,P, compound corresponding to the composition lZrP, + 1ZrP in which zirconium may occupy both phosphorus octahedra and trigonal prisms. Nevertheless, our attempts to synthesize such a binary compound were unsuccessful; the presence of a third element such as nickel in the tetrahedral sites between the phosphorus octahedra and trigonal prisms seems necessary to stabilize such a compound. A and B layers of trigonal prisms have also been reported in the chemistry of uranium, e.g. in the binary compound UIs [8]. However, only the iodine trigonal prisms are occupied by uranium atoms (Fig. 3(b)); all the other iodine polyhedra are unoccupied and the sequence between the A and B layers is -act-te-act-tet-. It should be noted that the ternary compound FeUSs is structurally analogous to U13 with iron atoms in octahedral sulphur sites [9]. Nevertheless the arrangement of the A and B layers in the binary compound U13 differs from that observed in Ni,Zr,P,. If we want to obtain the same sequence -act-oct-tet-tetbetween the A and B layers as in NisZr,P,, all the prisms in one of the two layers must be rotated through 180” (Fig. 3(c)).

5. Physical properties

5.1. Results Magnetic measurements were performed using the Faraday method. The magnetic susceptibilities were measured as a function of temperature from 85 to 290 K at a field strength of 5 kOe. All four compounds exhibited almost temperature-independent paramagnetism. The susceptibilities of NisZr?Ps, after correction for the core diamagnetism, were 0.31 X lop6 e.m.u. g-l and 0.27 X lop6 e.m.u. g-l at 85 K and 290 K respectively. Electrical measurements were made on NisZr,Ps needles about 2 mm long with a cross section of 3 X 10e2 mm by 3 X 10e2 mm (Fig. 4). The longitudinal resistivity pi, along the b axis of the single crystal, corresponding to the stacking of the [ZriP,] prisms, was measured between 4 and 293 K by the four-point method using silver-painted contacts and a direct current. The results given in Fig. 5 show that this compound exhibits metallic behaviour: the pii values vary between 1.9 X 10m4 a cm at 4 K and 3.2 X 10m4 52 cm at 290 K.

194

0.5mm. ,s,o ;

Fig. 4. Arrangement of Ni3Zr2P3 needles for resistivity measurements.

Plo-‘fl

cm

i

1.5 0

1 100

I ZOO

TK

Fig. 5. Electrical resistivity p 11 of Ni$k2P3 along the [ 010 ] direction.

5.2. Discussion The magnetic and electrical measurements show the metallic character of these new compounds. As can be seen in Table 4, there is no direct interaction between the phosphorus atoms in contrast with the large number of metal-metal and metal-non-metal bonds with the 12coordinated Goldschmidt atomic radii of zirconium (1.60 A) and nickel (1.24 A) and the tetrahedral covalent radius of phosphorus (1.10 A). The packing results in

195

very high coordination numbers for the metal atoms (Table 5). Zirconium atoms are surrounded by six phosphorus, two zirconium and five or nine nickel neighbours, the highest coordination corresponding to the ZrI atom. Nickel atoms have four phosphorus and six or eight metal neighbours as shown in Fig. 6. Phosphorus atoms are correlated to seven, eight or nine metal neighbours corresponding to a bicapped pyramidal, tricapped trigonal or bicapped trigonal prismatic coordination for PI, Pn and Pm respectively. TABLE 5 Coordination number in Ni&rzPs Atom

NNi

Nzr

NP

Sum

ZrI

9

Zm NiI NiII Ni,, PI PI1 PIII

5 3 2 3 2 6 4

2 2 5 4 5 5 3 4

6 6 4 4 4

17 13 12 10 12 7 9 8

Fig. 6. Representation

of the coordination of the metallic atoms in the structure.

6. Conclusion The type has obtained element,

discovery of new ternary arsenides and phosphides of the Ni3Zr2P3 led us to consider the existence of a new family of compounds by the substitution of zirconium (or hafnium) by a rare earth as previously observed in NilZZr2P, [lo - 121 and N&&PI3 [13]

196

where the zirconium atoms are in trigonal phosphorus sites. Our attempts to substitute the ZrI and Zrn atoms into Ni3Zr2P3 by rare earth elements resulted in mixtures in which the well-known LnNi*P,-type compounds are predominant [14,15], while the substitution of one of the two zirconium atoms is possible and gives quaternary compounds such as Ni3ZrLnP, which are isostructural with NisZr,Ps [ 161.

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