Thermo-Raman and dielectric constant studies of CaxBa1−xTiO3 ceramics

Thermo-Raman and dielectric constant measurements were carried out simultaneously on ceramic CaxBa1−xTiO3 (x=0–0.3) by coupling a thermo-Raman spectrometer with an LCR meter to study the effect of Ca substitution on the phase transformation and dielectric constant properties. The differential thermo-Raman intensity (DTRI) thermograms obtained from thermo-Raman intensity (TRI) showed the phase transformation temperature Tp for tetragonal to cubic (T–C) transformation. The temperature dependence of dielectric constant exhibits a peak at a temperature Tm, defined as ferroelectric transformation temperature for ferroelectric to paraelectric (F–P) transformation. The simultaneous measurement of thermo-Raman spectra and dielectric constant showed the consistency of Tp and Tm. This result indicates that the maximum dielectric constant occurred at the maximum rate of T–C phase transformation. The variation of dielectric constant with temperature for samples with different Ca concentration exhibited sharp transformation at Tm and no characters of diffuse transformation were noticed. Both Tm and Tp increased initially and reached maximum at 136 °C for x=0.15 and then decreased with further increase in Ca concentration. The variation in Tm with Ca concentration can be attributed to the competition between effects of increasing atomic polarisability and the shrinkage of unit cell volume due to the increasing Ca concentration.