Ln2Sr2PtO7+δ (Ln =La, Pr, and Nd): Three new Pt-containing [A2′O1+δ] [AnBn−1O3n]-type hexagonal perovskites

Polycrystalline samples of Ln2Sr2PtO7+δ (Ln=La, Pr, Nd) were prepared by conventional solid state synthesis. The three compounds are new examples for n  =2 members of the [A2′O1+δ][AnBn−1O3n] family of hexagonal perovskites containing platinum as the B  -type cation. XRD Rietveld refinements show the platinates to crystallize in space group R3¯ 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-LIII 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 La2Sr2PtO7+δ to be diamagnetic as expected for Pt4+ with low-spin (t2g6) configuration. For Ln=Pr and Nd the observed strong paramagnetism can be explained solely by the magnetic moments of the rare earths.

Graphical abstractHexagonal perovskites of the [A2′O1+δ][AnBn−1O3n] family have so far only been known for the transition metals Mn, Nb, Ru, and Ir. In this paper, three new n=2 examples containing platinum as B-type cation are presented. The structure and physical properties of the three title compounds were investigated by XRD Rietveld refinements, thermogravimetry, X-ray absorption spectroscopy, magnetic measurements and optical spectroscopy.Figure optionsDownload full-size imageDownload as PowerPoint slide