Ternary systems Sr–{Ni,Cu}–Si: Phase equilibria and crystal structure of ternary phases

Abstract

Phase relations were established in the Sr-poor part of the ternary systems Sr–Ni–Si (900 °C) and Sr–Cu–Si (800 °C) by light optical microscopy, electron probe microanalysis and X-ray diffraction on as cast and annealed alloys. Two new ternary compounds SrNiSi 3 (BaNiSn 3-type) and SrNi 9− x Si 4+ x (own-type) were found in the Sr–Ni–Si system along with previously reported Sr(Ni x Si 1− x ) 2 (AlB 2-type). The crystal structure of SrNi 9− x Si 4+ x (own-type, x=2.7, a=0.78998(3), c=1.1337(2) nm; space group P4/ nbm) was determined from X-ray single crystal counter to be a low symmetry derivative of the cubic, parent NaZn 13-type. At higher Si-content X-ray Rietveld refinements reveal the formation of a vacant site (□) corresponding to a formula SrNi 5.5Si 6.5□ 1.0. Phase equilibria in the Sr–Cu–Si system are characterized by the compounds SrCu 2− x Si 2+ x (ThCr 2Si 2-type), Sr(Cu x Si 1− x ) 2 (AlB 2-type), SrCu 9− x Si 4+ x (0≤ x≤1.0; CeNi 8.5Si 4.5-type) and SrCu 13− x Si x (4≤ x≤1.8; NaZn 13-type). The latter two structure types appear within a continuous solid solution. Neither a type-I nor a type-IX clathrate compound was encountered in the Sr–{Cu,Ni}–Si systems. Structural details are furthermore given for about 14 new ternary compounds from related alloy systems with Ba.