Refinement of the Crystal Structures of Palladium-rich In-Pd Compounds by X-Ray and Neutron Powder Diffraction

Abstract

Abstract The ternary indium palladium intermetallics In3Pd5, InPd2, and InPd3 have been synthesized by iodine-catalyzed reactions from the elements. Rietveld refinements on X-ray powder diffraction patterns provide the first accurate crystal structure data for In3Pd5 (Pbam, No. 55, a = 1104.20(2), b = 561.346(8), c = 424.263(6) pm, Rh5Ge3-type) and InPd2 (Pnma, No. 62, a = 561.676(6), b = 421.710(4), c = 822.78(8) pm, Co2Si-type). X-Ray powder diffraction apparently confirms the TiAl3 structure type proposed in the literature for InPd3. However, Rietveld refinement on neutron powder diffraction data reveals an In/Pd distributional disorder. Therefore, we describe the crystal structure of InPd3 in a AuCu-type model instead (P4/mmm, No. 123, a = 287.224(4), c = 380.079(7) pm), with mixed occupancy of one crystallographic site by 50% In and 50% Pd. In contrast to In3Pd5 and InPd2, which can be considered to be line compounds, InPd3 shows a non-negligible homogeneity range with unit cell volumes ranging from 0.126132(5) nm3 for the indium-rich to 0.125474(8) nm3 for the palladium-rich In1+xPd3−x phases. Mean In-Pd distances in these indium palladium intermetallics range from 272.3 pm (In1 in In3Pd5) with coordination number 8 for indium to 281.2 pm for 12-coordinated In in InPd3.