On the system cerium–platinum–silicon

Abstract

Phase relations in the ternary system Ce–Pt–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ 18-Ce 5(Pt,Si) 4 ( Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ 3-Ce 2Pt 7Si 4 ( Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ 10-CePtSi 2 ( Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm 5Ge 4-type, the Ce 2Pt 7Ge 4-type and the CeNiSi 2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt 3Si (Pt 3Ge-type, C2 /m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ 16-Ce 3Pt 5Si (Ce 3Pd 5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ 17-Ce 3PtSi 3 (Ba 3Al 2Ge 2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce–Pt–Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ 13-Ce(Pt x Si 1− x ) 2, τ 6-Ce 2Pt 3+ x Si 5− x or τ 7-CePt 2− x Si 2+ x .