T* of Relaxor Ferroelectric (1 − x) Pb(Zn_1/3Nb_2/3)O₃‐xPbTiO₃ Single Crystals Revisited Using Brillouin Spectroscopy

Abstract

The relaxor characteristics of Pb[(Zn 1/3 Nb 2/3 ) 1-x Ti x ]O 3 (PZN-xPT) single crystals(with x=0 and x=0.08) are investigated by using temperature-dependent Brillouin scattering spectroscopy. The longitudinal acoustic(LA) mode shows typical relaxor behaviors for PZN while its mode frequency exhibits a discontinuous change at the phase transition temperature(T C ) for PZN-8%PT. The transverse acoustic(TA) mode, which is forbidden in an ideal cubic phase at the backscattering geometry, appears in both samples at a certain temperature above either the dielectric maximum temperature(T m ) or T C . This breakdown of the Brillouin selection rule in the cubic phase indicates that the non-cubic polar regions become appreciable at this temperature where the interaction between the acoustic waves and the polar nanoregions (PNRs) is strong enough to enable the appearance of the TA mode. The intermediate characteristic temperature T* is determined in terms of the minimum of the temperature derivative of the half width of the LA mode, and the values were nearly the same as those determined via the acoustic emission signal measurements. These comparisons reveal the universal feature of the local phase transformation from dynamic to quasistatic PNRs at T*, giving rise to the appearance of the TA mode.

On the question of the critical end point in the (1 − x)PbMg1/3Nb2/3O3-xPbTiO3 relaxor ferroelectric single crystals based on acoustic emission data studies

“…Such a chemical disorder is known to be a reason to give rise to quenched random electric fields [2], which in turn is a reason of nucleation of polar nanoregions (PNRs) [3]. It is well documented that in the case of canonical RFEs the PNRs nucleate below the high-lying Burns temperature, start to grow below intermediate temperature, provide a huge, smeared and frequency-dependent maximum of the dielectric constant, ε, at temperature T m [4][5][6], and freeze below a glass temperature, T g [6], into a mesoscopic dipolar glass ground state [7], as the temperature decreases. While, in the case of non-canonical RFEs with FEs doping, the freezing temperature is replaced by the Curie temperature, T c , of a spontaneous FE phase transition, as the temperature decreases [1,6].…”