Light scattering study of acoustic phonon modes and central peaks in Pb[(Mg1∕3Nb2∕3)0.45Ti0.55]O3 single crystals

Abstract

The dynamic polar nanoregions ͑PNRs͒ which form below the Burns temperature and determine the unique properties of relaxor ferroelectrics were predicted ͓Tinte et al., Phys. Rev. Lett. 97, 137601 ͑2006͔͒ to be pinned to the quenched chemically ordered regions ͑CORs͒ usually observed in lead-containing relaxors. In Pb͓͑Mg 1/3 Nb 2/3 ͒ 0.45 Ti 0.55 ͔O 3 crystal where CORs are known to be absent, we have found the phenomena typically related to the relaxation of dynamic PNRs, namely, the significant Brillouin quasielastic scattering, the softening of the longitudinal acoustic mode, and the deviation from the Curie-Weiss law above the Curie point. This implies that PNRs may appear in crystals without CORs.

Brillouin scattering studies of acoustic phonon modes and central peak in single-crystal Pb(Sc1/2Ta1/2)OSivasubramanian1, Kojima2 2012Phys. Rev. B

“…In relaxor ferroelectrics, CP that begins to appear well above T m is attributed to the relaxational dynamics of PNRs. 5,7 As shown in Fig. 7, the decrease in the width and increase in the integrated intensity of CP indicates critical slowing down of the relaxation time and increase in the correlations between the PNRs with decrease in temperature.…”

“…2 Extensive studies on the dynamical aspects of PNRs have been carried out in prototype RFEs such as Pb(Mg 1/3 Nb 2/3 )O 3 (PMN) and other related systems through neutron and light scattering studies. [3][4][5][6][7][8][9] Brillouin scattering studies in these systems directly revealed the dynamical features of the PNRs such as the slowing down of their relaxation time and the coupling between the polarization fluctuations and acoustic phonon modes through the appearance of central peak (CP) and softening of the acoustic phonon mode. [6][7][8][9] This paper focuses on micro-Brillouin scattering studies on the dynamical aspects of PNRs in partially ordered Pb(Sc 1/2 Ta 1/2 )O 3 (PST) without any Pb vacancies.…”

Role of dynamic polar nanoregions in heterovalent perovskite relaxor: Inelastic light scattering study of ferroelectric Ti rich Pb(Zn1/3Nb2/3)O3-PbTiO3

“…In both heating and cooling processes, a significant softening of the LA mode and a clear anomaly corresponding to the cubic-tetragonal phase transition are observed at 481 K (T C-T ), which can be attributed to the interaction between the LA mode and the polarization flipping inside the dynamic PNRs. 16 The observed anomalous temperature dependence is similar to that of PMN-55PT with no COR, 15,28 while such a sharp elastic anomaly is uncharacteristic in typical RFEs such as PMN, PZN with CORs. In addition, LA shows a mild softening below T B $ 700 K, demonstrating that only normal anharmonic effects dominate in the lattice dynamics above T B .…”

“…The temperature dependence of C LA , which is related to the acoustic damping of the LA mode, shows the sharp increase near T C-T , suggesting the increase of scattering of the LA mode by the growth of dynamic PNRs. 15,16 …”

“…In PMN-xPT, the elastic anomaly owing to the interaction between the longitudinal acoustic (LA) mode and dynamic PNRs was still observed in PMN-55PT, i.e., with a PT content beyond the MPB composition. 15 Recent report on the acoustic emission (AE) of Pb-based relaxors at T* $ 500 K suggests that the martensitic transformation of PNRs generates AE bursts that were detectable by the ultrasonic transducer in the kilohertz range. 14 While the Brillouin scattering technique probes, the acoustic modes in the gigahertz range with a wavelength much shorter than that of the standard ultrasonic detection.…”