The ternary system cerium–rhodium–silicon

Abstract

Phase relations have been established in the ternary system Ce–Rh–Si for the isothermal section at 800 °C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 °C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ 7—Ce 3RhSi 3, (Ba 3Al 2Ge 2-type), τ 8—Ce 2Rh 3− x Si 3+ x (Ce 2Rh 1.35Ge 4.65-type), τ 10—Ce 3Rh 4− x Si 4+ x (U 3Ni 4Si 4-type), τ 11—CeRh 6Si 4 (LiCo 6P 4-type), τ 13—Ce 6Rh 30Si 19.3 (U 6Co 30Si 19-type), τ 18—Ce 4Rh 4Si 3 (Sm 4Pd 4Si 3-type), τ 21—CeRh 2Si (CeIr 2Si-type), τ 22—Ce 2Rh 3+ x Si 1− x (Y 2Rh 3Ge-type) and τ 24—Ce 8(Rh 1− x Si x ) 24Si (Ce 8Pd 24Sb-type). For τ 25—Ce 4(Rh 1− x Si x ) 12Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ 3—CeRhSi 2 (CeNiSi 2-type) and τ 6—Ce 2Rh 3Si 5 (U 2Co 3Si 5-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ 4—Ce 22Rh 22Si 56, τ 5—Ce 20Rh 27Si 53 and τ 23—Ce 33.3Rh 58.2−55.2Si 8.5−11.5 are unknown. High temperature compounds with compositions Ce 10Rh 51Si 33 (U 10Co 51Si 33-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 °C.