Phase transformation and the type of lattice distortion of some platinum-rich phases belonging to the Cu family

Abstract

Two different types of lattice distortion are observed in the platinum-rich phases with aluminium, gallium and indium. While in the binary phases Pt 3Al(l) and Pt 3Ga(l) (homeotypic with the Ir 3Si structure), the tetragonal substructure lattice distortion shows the values c/ a>1, the ternary platinum-based representatives of the CuAu type significantly show the values of the axial ratio c/ a≪1. This tetragonal lattice distortion increases with increasing valence electron concentration. No continuous solid solution between the homologous isostructural phases Ni 3Al and Pt 3Al(h) was found either by means of rapid liquid quenching or by heat treatment of the alloys Ni 0.75− x Pt x Al 0.25. The ternary phase NiPt 2Al (CuAu type) occurs in the composition range 0.37≤ x Pt≤0.50. Structural and powder diffraction data are presented for the ternary phases NiPt 2Al, Pt 2CuAl and Pt 2CuGa (CuAu type).