Raman study of Ba0.7Ca0.23TiO3 single crystals

Congruently grown barium calcium titanate, Ba0.77Ca0.23TiO3 (BCT77/23) can be fabricated as high optical quality single crystals, possess large electro-optic coefficients and high holographic sensitivity making it excellent candidate for various photorefraction based applications. Another great advantage of BCT is that the tetragonal-ortorhombic phase transition, which is destructive in BaTiO3, is depressed in BCT 77/23. In the present work we report on Raman study of BCT 77/33 crystals have been performed in the temperature region between 420K-10K. To our knowledge, this is first Raman light scattering study of BCT 77/23. We believed to gain insight on the nature of the cubic-tetragonal ferroelectric phase transition (PT) in BCT 77/23, on the role of Ca admixture, and search manifestations of the possible low temperature tetragonal-orthorhombic PT has been reported in [4]. A special attention was paid to detailed studies of the low energy region 5 200 cm-1 and to temperature evolution of A and E components of the 15 modes. A detailed polarization analysis was performed. The integrated intensities and bandwidth are deduced from fitting analysis. The data regarding the cubic-tetragonal PT are in agreement with previous results about dielectric permittivity confirming the complex nature of these phase transitions. The Raman data at lower temperatures give no clear indications about the occurrence of the T-O PT, at least down to 10 K. In addition weak features around 100 cm-1 were found, which are not observed in BaTiO3 matrix and probably arising from the presence of Ca ions.