On the system cerium–platinum–silicon

摘要

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 τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (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 Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-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 τ13-Ce(PtxSi1?x)2, τ6-Ce2Pt3+xSi5?x or τ7-CePt2?xSi2+x.