Effect of powder synthesis procedure on calcium site occupancies in barium calcium titanate: a rietveld analysis

Abstract

(Ba,Ca)TiO₃ samples with the ratio of (Ba+Ca) to Ti as unity but prepared by (i) a semiwet route involving (Ba,Ca)CO₃ solid solution precursors and TiO₂ and (ii) the conventional dry route involving BaCO₃, CaCO₃, and TiO₂ powders, exhibit diffuse and BaTiO₃-type sharp ferroelectric phase transitions, respectively. Rietveld analysis of neutron powder diffraction data from the two types of samples shows that, whereas in the samples prepared by the semiwet route, Ca²⁺ exclusively occupies the Ba²⁺ site, nearly half of the substituted Ca²⁺ occupies the Ti⁴⁺ site in the case of samples prepared by the dry route. We show that Ca replacement at the Ba site leads to diffuseness whereas Ca introduction at the Ti site leads to sharpening of the transition. To our knowledge, this is the first clear demonstration of the powder synthesis procedure affecting the substitutional sites in multicomponent ceramics and this, in turn, influencing their physical behavior drastically.