Investigations related to the incorporation of Ca2+ ions into the BaTiO3 lattice

Dependence of the composition of (100−x) BaTiO3 +xCaTiSiO5 precursor (x = 2–16 mol%) mixtures on calcination temperature was investigated by means of X-ray diffraction and differential scanning calorimetry. The formation of a secondary phase, fresnoite (Ba2TiSi2O8), starts at about 900 °C. The resulting Ba and O vacancies and the produced microstress stabilize the pseudocubic phase of BaTiO3 at room temperature. Temperatures higher than 1200 °C are necessary to incorporate Ca ions into the BaTiO3 crystals forming (Ba, Ca) TiO3 solid solutions. As a result the lattice becomes free of tension and the BaTiO3 based ceramics transform into thermodynamically stable tetragonal phases at room temperature.