Crystal Structure of Nd_10.67Pt₄O_24, a New Neodymium Platinate

A new platinate was recently discovered when Nd₂O₃ was explored as a platinum capture material in the Ostwald process, formed by a direct reaction between gaseous PtO₂ and Nd₂O₃. The crystal structure of this new platinate and its composition, Nd_10.67Pt₄O₂₄, are here reported for the first time. The compound is synthesized either by a direct reaction between PtO₂(g) and Nd₂O₃ or by the citric acid chemical route. Based on 3-dimensional electron diffraction data and Rietveld refinement of high-resolution synchrotron and neutron powder diffraction data, we describe its crystal structure in space group I4₁/a. The compound is structurally related to the Ln_11- Sr Ir₄O₂₄ (Ln = La, Pr, Nd, and Sm) phases with a double perovskite (A₂BB'O₆)-like crystal structure with A-site cation deficiency. Owing to the fixed oxidation state of Pt(IV), two of the four Nd sites are partly occupied to provide charge neutrality, with Nd4 taking a split position. On heating, Nd_10.67Pt₄O₂₄ decomposes into Nd₂O₃ and Pt. A plateau in the thermogravimetric curves measured in 33 vol % O₂ in N₂ indicates the presence of an intermediate Pt(II) phase at around 960 °C, probably isostructural with La₄PtO₇.