Ln2Sr2PtO7 + δ (Ln = La, Pr, and Nd):: Three new Pt-containing [A′2O1+δ] [AnBn-1O3n]-type hexagonal perovskites

Polycrystalline samples of Ln(2)Sr(2)PtO(7+delta) (Ln = La, Pr, Nd) were prepared by conventional solid state synthesis. The three compounds are new examples for n = 2 members of the [A ' O-2(1+delta)][A(n)B(n-1)O(3n)] family of hexagonal perovskites containing platinum as the B-type cation. XRD Rietveld refinements show the platinates to crystallize in space group R (3) over bar 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 (delta = 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 3.05eV, respectively. Magnetic measurements showed La2Sr2PtO7+delta to be diamagnetic as expected for Pt4+ with low-spin (t(2g)(6))configuration. For Ln = Pr and Nd the observed strong paramagnetism can be explained solely by the magnetic moments of the rare earths. (C) 2007 Elsevier Inc. All rights reserved.