PtIn6(GaO4)2-x (x0.2) - A NEW LOW VALENT INDIUM GALLATE CONTAINING PtIn6 OCTAHEDRA

Holger Friedrich and Jürgen Köhler

Max-Planck-Institut für Festkörperforschung, Heisenbergstrasse 1, 70569 Stuttgart
friedrich@vaxff2.mpi-stuttgart.mpg.de

Keywords: PtIn6 octahedra, gallate, Rietveld refinement, pentlandite structure, band structure

Reduced binary oxides and fluorides of indium are unknown. Recently, the first reduced complex indiumfluorides InBF4 [1], PtIn7F13 and Pt3In22F40 [2] have been discovered. The latter two contain PtIn6 octahedra as characteristic building units.

In order to prepare low valent complex indium oxides we concentrated our research on the investigation of the Pt­In­Ga­O system. X-ray diffraction measurements from a series of samples synthesized by heating intimate mixtures of Pt, In, In2O3 and Ga2O3 in an atmosphere of argon at 1220 K for 80 h showed in all cases reflections which could not be assigned to known compounds. However, they could be indexed with a face centered cubic unit cell.

The structure of the new compound was solved and refined with the Rietveld method in Fm3m with a=1001.8 pm [3]. The composition was determinated by chemical analysis to PtIn6(GaO4)1.8. In the new oxide there are also PtIn6 octahedra with Pt-In distances of 254 pm, which are significantly shorter than in Pt-In alloys, but similar to those found in PtIn7F13 and Pt3In22F40 (254 - 256 pm). Each Ga atom is surrounded by a regular tetrahedron of O atoms at 188 pm, comparable to the bond length in alkaline-metal gallates. The arrangement of the polyhedra can be obtained from the CaF2 structure by replacing Ca by PtIn6 octahedra and F by GaO4 tetrahedra (see Figure 1). This arrangement leads also to empty In6 octahedra. The In­In distances are 359 pm in the PtIn6 cluster and 349 pm in the empty In6 cluster. Both kinds of In clusters form together a three-dimensional network of corner-sharing octahedra. The In­O distance is 227 pm and slightly longer than in In2O3 (213 pm and 223 pm). The compound is isotypic to Co9S8 (and the mineral pentlandite (Fe,Ni)9S8) which according to [CoS6](SCo4)2 consists of CoS6 octahedra and SCo4 tetrahedra.

The composition of the new compound with full occupancy of all sites is PtIn6(GaO4)2 but until now we were only able to prepare PtIn6(GaO4)1.8 as a homogeneous product. Powder samples of PtIn6(GaO4)1.8 are black, stable in air and against non-oxidizing acids.

The electric and magnetic properties as well as the band structure on the basis of LMTO calculations will be discussed.

  1. H. Fitz, B. G. Müller, Z. Anorg. Allg. Chem. 623 (1997) 579
  2. J. Köhler and J.-H. Chang, 5. Jahrestagung der DGK, Referateband (1997) 12
  3. L. G. Akselruud, Y. N. Grin, P. Y. Zavalij, V. K. Pecharsky and V. S. Fundamenskii: CSD - Universal program package for single crystal and/or powder structure data treatment

Figure 1: Arrangement of PtIn6 octahedra and GaO4 tetrahedra in PtIn6(GaO4)2-x (x 0.2)