Thermal decomposition of the mixed carbonate solid solution Ca1 - x-Mnx CO3 (0.0 ≤ x ≤ 1.0) at 1273 K in hydrogen results in the respective oxide solid solutions Ca1 - xMnxO. Thermolysis at temperatures less than 1173 K of the homogeneous carbonate phase, Ca1 - xMnxCO3 (x = 0.5) results in incomplete solid solution and a calcium and manganese oxiderich mixture. The miscibility gap extends from 25 to 85 mol% MnO at 873 K. The decomposition reactions were conducted in a hydrogen atmosphere in order to maintain manganese in the divalent state. These results are compared with earlier decomposition studies conducted at reduced pressures of carbon dioxide and in vacuo. The important role of the decomposition mechanism in the application of the solid solution precursor method to solid state reactions is emphasized.
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