Raman spectroscopy of bulk and thin-layer (Ba,Sr)TiO3 ferroelectrics

A comparative Raman study of (Ba,Sr)TO3 bulk ceramics, sol-gel derived polycrystalline thin film, and heteroepitaxial thin film deposited by rf sputtering onto (001) MgO substrate is reported. It is found that phase transition sequence in the heteroepitaxial thin film is markedly different from those observed in the bulk ceramics and polycrystalline thin film.