The ternary system cerium–palladium–silicon

Phase relations in the ternary system Ce–Pd–Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction and EMPA techniques on about 130 alloys, which were prepared by arc-melting under argon or powder reaction sintering. Eighteen ternary compounds have been observed to participate in the phase equilibria at 800 °C. Atom order was determined by direct methods from X-ray single-crystal counter data for the crystal structures of τ8—Ce3Pd4Si4 (U3Ni4Si4-type, Immm; a=0.41618(1), b=0.42640(1), c=2.45744(7) nm), τ16—Ce2Pd14Si (own structure type, P4/nmm; a=0.88832(2), c=0.69600(2) nm) and also for τ18—CePd1−xSix (x=0.07; FeB-type, Pnma; a=0.74422(5), b=0.45548(3), c=0.58569(4) nm). Rietveld refinements established the atom arrangement in the structures of τ5—Ce3PdSi3 (Ba3Al2Ge2-type, Immm; a=0.41207(1), b=0.43026(1), c=1.84069(4) nm) and τ13—Ce3−xPd20+xSi6 (0≤x≤1, Co20Al3B6-type, Fm3¯m; a=1.21527(2) nm). The ternary compound Ce2Pd3Si3 (structure-type Ce2Rh1.35Ge4.65, Pmmn; a=0.42040(1), b=0.42247(1), c=1.72444(3) nm) was detected as a high-temperature compound, however, does not participate in the equilibria at 800 °C. Phase equilibria in Ce–Pd–Si are characterized by the absence of cerium solubility in palladium silicides. Mutual solubility among cerium silicides and cerium–palladium compounds are significant whereby random substitution of the almost equally sized atom species palladium and silicon is reflected in extended homogeneous regions at constant Ce-content such as for τ2—Ce(PdxSi1−x)2 (AlB2-derivative type), τ6—Ce(PdxSi1−x)2 (ThSi2-type) and τ7—CePd2−xSi2+x. The crystal structures of compounds τ4—Ce~8Pd~46Si~46, τ12—Ce~29Pd~49Si~22, τ15—Ce~22Pd~67Si~11, τ17—Ce~5Pd~77Si~18 and τ18—CePd1−xSix (x~0.1) are still unknown.