Synthesis and crystal structure of Mg_1-x Cu_2+xO₃(0.130≤×≤0.166)

Solid solutions of Mg_1-xCu_2+xO₃ were prepared at 950°C for 12 h in air with a narrow composition range of x from 0.130 to 0.166. Thermal analysis revealed that the sample of x = 0.143 decomposed into MgO and Cu₂O above 1030°C. The stoichiometric oxygen content based on Cu II valence was confirmed with the weight loss after decomposition in H₂:Ar (20%:80%) atmosphere. The X-ray powder diffraction pattern of the sample (x = 0.143) was analyzed by the Rietveld method. The structure is isostructural with CaCu₂O₃, and related to a rock-salt-type superstructure with an orthorhombic cell, a = 3.9906(1), b = 9.3482(3), and c = 3.1911(1) Å, space group Pmmn (No. 59, setting 2). There are two metal atom sites in the structure. One metal atom site (4e) occupied by Cu atoms is in an elongated octahedron of oxygen atoms. The other site (2b) is statistically occupied by Cu and Mg atoms with fractions of 0.143 and 0.857, respectively.