Ln2Sr2PtO7+δ (Ln=La, Pr, and Nd): Three new Pt-containing [AnBn−1O3n]-type hexagonal perovskites

Polycrystalline samples of Ln₂Sr₂PtO_7+δ (Ln=La, Pr, Nd) were prepared by conventional solid state synthesis. The three compounds are new examples for n=2 members of the A_nB_n−1O_3n] family of hexagonal perovskites containing platinum as the B-type cation. XRD Rietveld refinements show the platinates to crystallize in space group and, in the case of Pr and Nd, revealed a complete ordering of Ln/Sr on the two distinct A-type positions, while for La a partial disorder was observed. By XANES investigations at the Pt-L_III threshold the oxidation state +4 for platinum was found. Thermogravimetry revealed a small oxygen excess for Ln=La and Pr (δ=0.13 and 0.07), pointing to the presence of peroxide ions as already observed for isostructural Ru- and Ir-based compounds. UV–Vis measurements were done for the yellow lanthanum and the green neodymium compound. They revealed two optical band gaps of 2.52 and 3.05 eV, respectively. Magnetic measurements showed La₂Sr₂PtO_7+δ to be diamagnetic as expected for Pt⁴⁺ with low-spin configuration. For Ln=Pr and Nd the observed strong paramagnetism can be explained solely by the magnetic moments of the rare earths.