Crystal structure of Nd10.67Pt4O24, a new neodymium platinate

Abstract

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 PtO2(g) and Nd2O3. The crystal structure of this new platinate and its composition, Nd10.67Pt4O24 , are here reported for the first time. The compound is synthesized either by a direct reaction using PtO2(g) 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 accurately describe its crystal structure in space group I41/a. The compound is structurally related to the Ln11-xSrxIr4O24 (Ln = La, Pr, Nd, Sm) phases with a double-perovskite (A2BB'O6) like crystal structure and 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 the Nd4 site taking a split position. On heating, Nd10.67Pt4O24 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 {\deg}C, probably isostructural with La4PtO7.