Broadband light scattering of two relaxation processes in relaxor ferroelectric0.93Pb(Zn1/3Nb2/3

Abstract

Dynamical properties of relaxor ferroelectric 0.93Pb͑Zn 1/3 Nb 2/3 ͒O 3 -0.07PbTiO 3 single crystals have been studied by the broadband inelastic light scattering from gigahertz to terahertz frequency range. The longitudinal-and transverse-acoustic ͑LA and TA͒ phonon frequencies deviate below the Burns temperature T B = 736 K from a linear temperature dependence above T B , indicating the existence of polarization relaxations induced by the polar nanoregions ͑PNRs͒. On further cooling, a central peak ͑CP͒ which originates from the relaxations in the PNRs is observed clearly below 600 K Ͻ T B . The CP width decreases markedly down to T ‫ء‬ = 499 K and the change in the CP width becomes mild below T ‫ء‬ . The slower ͑ϳ10 −12 s͒ and faster ͑ϳ10 −13 s͒ relaxation times determined by the CP show good agreement with the relaxation times determined by TA and LA phonons, respectively. 180°and non-180°͑71°and 109°͒ polarization flippings are allowed in the PNRs with the polar rhombohedral symmetry. Considering the piezoelectric coupling in a PNR, it is suggested that 180°flipping is related to the relaxation observed in LA phonon, while non-180°flipping is related to that in TA phonon.

Development of nanoscale polarization fluctuations in relaxor-based (1-x)Pb(Zn1/3Nb2/Tsukada1, Hidaka2, Kojima3 et al. 2013Phys. Rev. BSelf Cite252250View full textAdd to dashboardCite

“…This peak is also a characteristic of relaxor ferroelectrics, and its interpretation was discussed in our previous works. 17,19,20,22 To extract the frequency shift and width of the LA phonon from the light scattering spectra, we used the Voigt function. The width of a Gaussian component in the Voigt function was fixed as an instrumental function.…”

“…We can therefore conclude that the LA phonon anomaly at T * is an intrinsic effect. [18][19][20]22 We attribute the elastic anomaly in the paraelectric phase to the polarization fluctuation through the piezoelectric coupling. This is described in Eq.…”

“…However, ferroelectric materials with disorder, e.g., relaxor ferroelectrics and barium titanate-(BaTiO 3 -) based ferroelectrics show the anomaly in a much wider temperature range. [17][18][19][20]22,[31][32][33] We attribute the anomaly to a piezoelectric coupling inside the noncentrosymmetric disordered regions. Because the local structure inside the PNRs is noncentrosymmetric, 3,12,13 even though the matrix around the PNR is centrosymmetric, the polarization fluctuation can couple linearly with the strain fluctuation.…”

“…In our previous study, the relaxation observed at the central peak was related to the acoustic anomalies observed in PZN-0.07PT. 20 A comprehensive explanation of the acoustic anomalies of relaxor ferroelectrics is presented in this paper, which is based on the determination of the relaxation times of polarization fluctuations that couple to the strain fluctuations in the PZN-xPT crystals. The dynamic correlation length of the relaxation time is also discussed.…”

“…Thus, dielectric measurement, inelastic light scattering (both Brillouin and Raman scatterings), inelastic neutron scattering, and inelastic x-ray scattering have been performed in various studies. 11,[14][15][16][17][18][19][20][21][22][23] Of note, the study of acoustic phonons in ferroelectric materials is one of the most powerful approaches for investigating the polarization fluctuations related to a ferroelectric phase transition. 24 This is because acoustic properties are influenced by polarization fluctuations through strainpolarization coupling.…”