Precursor polar clusters in the paraelectric phase of ferroelectric Ba0.80Ca0.20TiO3 single crystals studied by Brillouin light scattering

A strong relaxation mode was observed in the gigahertz frequency window in the paraelectric phase of Ba0.80Ca0.20TiO3 single crystals by using Brillouin light scattering. The appearance and growth of this relaxation mode were accompanied by substantial softening of the longitudinal acoustic mode as well as a remarkable increase in the hypersonic damping. Similar to BaTiO3, the temperature dependence of the relaxation time of Ba0.80Ca0.20TiO3 displayed a slowing-down behavior near the Curie temperature, indicating the order-disorder nature of the paraelectric-ferroelectric phase transition in this substance. The dynamics of precursor polar clusters observed in this work was discussed in relation with recent theoretical studies and found to be consistent with their predictions.