RESUMO
A series of lanthanide tungsten oxychlorides with compositions of La8.64W6O30.45Cl, Ce8.64W5.74O30Cl, Pr8.33W6O30Cl, and Nd8.33W6O30Cl was synthesized as single crystals via a high-temperature flux growth method. The reduction of Ce(IV) to Ce(III) was performed in the synthesis of Ce8.64W5.74O30Cl using Zn metal as the reducing agent. All four compounds crystallize in the tetragonal space group P42/nmc with a highly disordered and rather unusual arrangement of Ln(III) and W(VI) cations. The three-dimensional crystal structure consists of a complex network of Ln cations occupying multiple coordination environments, including LnO8 cubes. The level of complexity the disorder adds to the overall structure was considered using calculations for the total information content of the crystal. The temperature dependence of the magnetic susceptibility of Pr8.33W6O30Cl and Nd8.33W6O30Cl was measured, and both compounds exhibit paramagnetic behavior across the entire 2-300 K temperature range measured.
RESUMO
The crystal chemistry and magnetic properties for two triple perovskites, Ba3Fe1.56Ir1.44O9 and Ba3NiIr2O9, grown as large, highly faceted single crystals from a molten strontium carbonate flux, are reported. Unlike the idealized A3MM2'O9 hexagonal symmetry characteristic of most triple perovskites, including Ba3NiIr2O9, Ba3Fe1.56Ir1.44O9 possesses significant site-disorder, resulting in a noncentrosymmetric polar structure with trigonal symmetry. The valence of iron and iridium in the heavily distorted Fe/Ir sites was determined to be Fe(III) and Ir(V) by X-ray absorption near edge spectroscopy (XANES). Density functional theory calculations were conducted to understand the effect of the trigonal distortion on the local Fe(III)O6 electronic structure, and the spin state of iron was determined to be S = 5/2 by Mössbauer spectroscopy. Conductivity measurements indicate thermally activated semiconducting behavior in the trigonal perovskite. Magnetic properties were measured and near room temperature magnetic ordering (TN = 270 K) was observed for Ba3Fe1.56Ir1.44O9.