Compounds and subsolidus phase relations in the CaO–Co3O4–CuOCaO–Co3O4–CuO system

We have investigated the subsolidus phase relations in the system CaO–Co3O4–CuOCaO–Co3O4–CuO at 920∘C under 1 atm of oxygen by means of powder X-ray diffraction method. Apart from the three known phases of Ca2CuO3Ca2CuO3, Ca3Co2O6Ca3Co2O6 and (Co1-xCux)3O4Co1-xCux)3O4 spinel (0⩽x⩽0.06)(0⩽x⩽0.06), two misfit-layered cobaltates have been identified. The first misfit is a solid solution, having a chemical formula [Ca2(Co1-xCux)O3]pCoO2[Ca2(Co1-xCux)O3]pCoO2 with 0⩽x⩽0.120⩽x⩽0.12, while the other misfit has a pinpoint composition of [Ca2(Co0.65Cu0.35)2O4]pCoO2[Ca2(Co0.65Cu0.35)2O4]pCoO2. Both the phases have an incommensurate b  -axes ratio, p∼0.62p∼0.62, due to the size difference between the two subsystems. Another phase is found in the Cu-rich quasi-one-dimensional composite crystal Cap(Cu1-xCox)O2(p∼0.83,0.08⩽x⩽0.34), but the terminal compound Ca0.83CuO2Ca0.83CuO2 is not synthesized. The octahedral Co site in the Ca3Co2O6Ca3Co2O6 phase can be partially substituted with Cu, up to 6%, to form the Ca3(Co1-xCux)2O6(0⩽x⩽0.06) solid solution.

Subsolidus phase relations in the CaO–Co3O4–CuO pseudo-ternary system determined at 920∘920∘Figure optionsDownload as PowerPoint slide