On the preparation and crystal structure of a new form of PtGa < inf> 2

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The crystal structure of the silver-colored form of PtGa2 has been reported for the first time. It belongs to the space group I41/acd, with the lattice parameters a = 8.5544(4) and c = 21.574(17) Å, and Z = 32. The structure consists of layers of Pt and Ga stacked along the c axis, in which two crystallographically different Pt and Ga atoms have similar environments involving eight and nine nearest neighbors respectively. Based on some recent crystallographic data reported in the literature, this structural arrangement may be the prototype for a family of ternary platinum metal-Group B-based phases. The present investigation also necessitates changes in the currently accepted Ga-Pt phase diagram. According to the present study, stoichiometric PtGa2 undergoes a structural transformation upon cooling from a brass-colored fluorite structure to the silver-colored, tetragonal structure described above. However, transformation is inhibited if the composition of the fluorite-structured phase is Ga-poor. This behavior is reminiscent of that of defect-stabilized cubic ZrO2, which also possesses the fluorite structure.

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Journal of Alloys and Compounds