Crystal Chemistry of LuPd₂O₄ and Other Spinel-Related NdCu₂O₄-LaPd₂O₄-Type Compounds

Lutetium palladium oxide (LuPd2O4) has been prepared in a multianvil apparatus at 60 kbar pressure and 1000°C. It crystallizes in the tetragonal LaPd2O4-type structure with space group I41/a, a = 5.681(1) Å, c = 9.881(2) Å, and Z = 4. The structure of this compound, like that of NdCu2O4 and other members of this new class, is closely related to that of spinel except for the difference in oxygen arrangements, leading to a difference in coordination of the A, B, and O ions. It can be derived from spinel by oxygen displacements. A new version of Kugimiya and Steinfink's AB2O4 correlation map in the region 0.04 < Kab < 0.18 and 0.8 < ra/rb < 1.7, has been generated. It shows that the new AB2O4 class lies in the area between the spinel- and CaFe2O4-type regions.