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

Abstract

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.