Phase transition of polycrystalline BaTiO3 at high-pressure detected by a pulsed photoacoustic technique

Sound velocity changes of unpolarized polycrystalline BaTiO3, in the diamond anvil cell (DAC) up to 6.8 GPa, across the tetragonal to cubic phase transition at room temperature (RT) have been detected by a photoacoustic technique. The light absorption before, during, and after the structural phase transformation shows changes. This is very clear using a photoacoustic method where a pulsed laser is used as a standard source of ultrasound. The phase transition is recognized by a profile generated through sequence values of the temporal peak positions acquired from sequential measurements of the pulsed photoacoustic signal (PA) obtained for each pressure applied. The results are in agreement with those obtained by high-pressure Raman spectroscopy carried out under similar conditions. In both techniques a 4:1 methanol-ethanol mixture was used as a pressure transmitting medium, and the pressure was calibrated using the ruby fluorescence technique.