Elastic softening and central peaks in BaTiO_3 single crystals above the cubic-tetragonal phase-transition temperature

摘要

A strong relaxation mode was observed in the paraelectric phase of barium titanate (BaTiO_3) single crystals by Brillouin scattering study and was found to correlate with the softening of the longitudinal acoustic mode and the increase in the hypersonic damping. These observations support the existence of polar percursors and their electrostrictive coupling with the strain caused by the acoustic waves, consistent with former studies evidencing off-centered Ti ions in the high-symmetry cubic phase. A critical slowing down has been clearly observed in the vicinity of the cubic-tetragonal phase transition, indicating order-disorder component contributes to the phase transition of BaTiO_3.