Compounds and subsolidus phase relations in the CaO - Co3O 4-CuO system

Yuzuru Miyazaki, Xiangyang Huang, Tsuyoshi Kajitani

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We have investigated the subsolidus phase relations in the system CaO-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 Ca2CuO3, Ca3Co2O6 and (Co1-xCux)3O4 spinel (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 with 0≤x≤0.12, while the other misfit has a pinpoint composition of [Ca2(Co0.65Cu0.35)2O4]pCoO2. Both the phases have an incommensurate b-axes ratio, p∼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 Ca0.83CuO2 is not synthesized. The octahedral Co site in the Ca3Co2O6 phase can be partially substituted with Cu, up to 6%, to form the Ca3(Co1-xCux)2O6(0≤x≤0.06) solid solution.

Original languageEnglish
Pages (from-to)2973-2979
Number of pages7
JournalJournal of Solid State Chemistry
Issue number10
Publication statusPublished - 2005 Oct


  • Ca-Co-Cu-O system
  • Composite crystal
  • Crystal structure
  • Phase relations
  • Rietveld analysis
  • Solid solution
  • Thermoelectric compounds


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