Influence of a co-substituted A-site on structural characteristics and ferroelectricity of (Pb,Ba, Ca)TiO3 complex perovskites: analysis of local-, medium- and long-range order

Thin films of A-site co-substituted, PbTiO₃ (PTO) by Ba²⁺ and Ca²⁺, i.e., PBCT70, PBCT60, PBCT50 and PBCT40 were fabricated on Pt/Ti/SiO₂/Si substrates by chemical solution deposition. Structures of the samples were investigated from the viewpoint of local-, medium- and long-range order by X-ray absorption near structure (XANES), micro-Raman and infrared spectroscopies and by X-ray diffraction (XRD). The films thickness were determined by using field-emission scanning electron microscope. The experimental results demonstrate that BaO₁₂ clusters are the critical dominant ferroelectricity cause in PBCT thin films rather than CaO₁₂ clusters. XRD analysis which was applied to investigate the crystal symmetry indicates the absence of long-range structural distortion for samples at higher concentrations of Ba²⁺ and Ca²⁺. However, an analysis of structural medium- and local-range order such as infrared, micro-Raman and XANES spectroscopies revealed that symmetry changes are much more prominent; i.e., local structural distortions remain. Temperature-dependent dielectric permittivity measurements confirmed a decreasing ferroelectric-to-paraelectric phase transition temperature and showed a broad phase transition with an increase in BaO₁₂ and CaO₁₂ clusters. In addition, the lack of long-range polar ordering for the ferroelectric dipole caused by symmetry changes decreases the remanent polarization.