New Phases in the CaO–M 2 O 3 –CuO (M = Nd, Gd, Y) Systems at 1000°C

New layered cuprates with the general stoichiometry Ca 2+ x M 2− x Cu 5 O 10 have been characterized for M = Nd, Gd, and Y. These insulating phases have structures closely related to that of NaCuO 2 and contain one‐dimensional chains constructed from edge‐sharing [CuO 4 ] 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 Ca 2+ and M 3+ 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.