The mechanisms of decomposition for BaCO3, CaCO3 and SrCO3 are similar (although of course not at the same temperature; calcium carbonate, for example, is much lower than this). Decomposition of this material can be a concern (relating to glaze defects, for example) if the powder is used in ceramic clay bodies and contains granular +200 mesh material. This temperature is from Thermal Decomposition of Ionic Solids by Andrew K. Galwey, Michael E. Brown
Ceramic materials, especially clays, often contain carbon and organic compounds. When they are fired in a kiln, these must burn out, often producing complications.