Central peaks, acoustic modes, and the dynamics of polar nanoregions inPb[(Zn1∕3Nb2∕3

Abstract

Temperature dependence of acoustic behaviors and quasielastic central peaks ͑CPs͒ of Pb͓͑Zn 1/3 Nb 2/3 ͒ x Ti 1−x ͔O 3 ͑PZN-xPT͒ single crystals with x = 4.5% and 9% have been investigated in a temperature range of 300-900 K by using the Brillouin light scattering. The temperature dependence of the C 11 elastic constant of both crystals showed a deviation from normal lattice anharmonicity at the Burns temperature ͑T B ͒ of about 730 K upon cooling, indicating the onset of the electrostrictive coupling between the polar nanoregions ͑PNRs͒ and the longitudinal acoustic ͑LA͒ waves. Upon further cooling, depolarized CP began to appear at a certain temperature ͑T d ͒ located in 500-550 K, which was accompanied by substantial softening of the C 44 elastic constant below this temperature suggesting anisotropic electrostrictive coupling between PNRs and the two acoustic waves. In addition, the onset of significant increase in the acoustic damping of both acoustic waves at T d could be seen from the temperature dependence of the linewidth of Brillouin doublets. These results suggested that electrostrictive coupling of the strain to the square of the local polarization of PNRs and the resultant order-parameter fluctuations are enhanced not at T B but at a much lower temperature of T d , which may be ascribed to a local structural transformation occurring in PNRs at T d. This suggestion is consistent with recent studies on PZN-xPT single crystals reporting the appearance of strong acoustic emission signals ͓M. Roth et al., Phys. Rev. Lett. 98, 265701 ͑2007͔͒ and substantial changes in the Raman spectrum ͓O. Svitelskiy, Phys. Rev. B 72, 172106 ͑2005͔͒ at almost the same temperature. From the comparison of the present results to those of two typical relaxors, Pb͑Mg 1/3 Nb 2/3 ͒O 3 and Pb͑Mg 1/3 Ta 2/3 ͒O 3 , it was suggested that the existence of an intermediate characteristic temperature T d below T B may be considered as a more common characteristic in the temperature evolution of PNRs of relaxor ferroelectrics.

Relaxing with relaxors: a review of relaxor ferroelectrics

“…The behaviour of the hypersonic acoustic phonons in mixed crystals with x = 0.24 [187], 0.34 [188] and 0.35 [189] The results of Raman scattering from the mixed crystals are qualitatively similar to those of PMN, as shown in Figure 65, for x = 0, 0.09, 0.21, 0.28, 0.32 and 0.38 [96,[190][191][192][193][194][195]. Increasing the PT concentration to above x = 0.7 leads to a dramatic decrease in the intensity of the Raman scattering [192], presumably this is because the structure of the crystal becomes closer to that of the ideal perovskite structure for which there should be no first-order Raman scattering.…”

Elastic softening and central peaks in BaTiO3 single crystals above the cubic-tetragonal phase-transition temperature

“…24,25 The deviation of the elastic constant from the normal anharmonic behavior at high temperatures is correlated to the formation of dynamic PNRs at the so-called Burns temperature. 24 As the PNRs become long lived with longer correlation length with decreasing temperature, electrostrictive coupling between the squared polarization of PNRs and the strain caused by the acoustic waves become stronger resulting in the substantial softening of B and the increase in the hypersonic damping. Similar scenario can be applied to the interpretation of the acoustic anomalies observed from BaTiO 3 .…”

Effect of chemically ordered regions on the acoustic behaviors in Pb(Mg1/3Nb2/3)O3 studied by Brillouin scattering

“…7 In addition, additional characteristic temperature other than T m and T B in the temperature evolution of PNRs has been suggested based on several experiments. [8][9][10] PNRs have been considered to be responsible for the complex structural and dynamical characteristics of RFEs.…”