Order-disorder nature of lithium tantalate probed by broadband Brillouin scattering spectroscopy

Lithium tantalate LiTaO₃ (LT) crystals are well known ferroelectrics, however the mechanism of the ferroelectric phase transition is still unclear. Although the relaxation mode has been reported, there is no experimental evidence related to the critical slowing down in the vicinity of T_C. We studied both congruent and nearly stoichiometric LT crystals using broadband Brillouin scattering. The nearly stoichiometric crystal clearly shows the critical slowing down in the vicinity of T_C, while it is suppressed in the congruent one with high defect density at the Li site. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)