On the crystal parameters of some representatives of the NiAs family containing platinum group metals and gold

Abstract

Abstract Unit cell parameters were investigated for the palladium/platinum and the B13…B16 element-containing representatives of the Ni2In, NiAs and CdI2 types in the whole range of homogeneity. For phases belonging to the defect Ni2In type, macroscopic density was also measured to determinate the number of atoms in the unit cell. For the homologous phases Pd2Sn(h) and Pd5Pb3(h2), it has been found that the tin-containing compound shows (at the same Pd/B metal stoichiometry) a higher number of atoms in the unit cell than the lead-containing phase. The d electron concentration of the late transition metals controls predominantly the values of the axial ratio c/a: rhodium and iridium-containing representatives of the NiAs family (possessing the same B element) show a higher c/a ratio than corresponding palladium and platinum-containing phases. Comparing the quasihomologous stannides IrSn, PtSn and AuSn, the largest difference between the sum of atomic radii and the measured shortest atomic distance, Δd = (r A + r B) – d A–B, is observed for IrSn and the smallest one for AuSn. Regarding this, the iridium and platinum-containing stannides possess obviously a larger charge transfer as well as a stronger bond energy than the gold containing compound.