New Phases in the CaO–M2O3–CuO (M = Nd, Gd, Y) Systems at 1000°C

New layered cuprates with the general stoichiometry Ca_{2+ x} M_{2− x} Cu₅O₁₀ have been characterized for M = Nd, Gd, and Y. These insulating phases have structures closely related to that of NaCuO₂ and contain one-dimensional chains constructed from edge-sharing [CuO₄] square planes. The X-ray patterns of these ternary cuprate phases are complicated by strong reflections from both incommensurate and commensurate supercells which result from the ordering of the Ca²⁺ and M³⁺ ions in the structure. The stoichiometry range, and resultant Cu valences in these cuprates depend upon the nature of the trivalent ion. Ca-rich and trivalentrich compositions can be prepared for M = Nd and Gd, but only Ca-rich compositions were formed in the Y system. No other ternary phases are observed under the conditions of this study, 1000°C in air, and the solid-state equilibria are dominated by the single ternary phase identified above.