High-pressure Brillouin scattering of the single-crystal PbSc_{1/2}Ta_{1/2}O_{3} relaxor ferroelectric

Pressure-induced structural transformations in advanced ferroelectrics with relaxor behaviour

“…5c) [16,24,25] and the transverse acoustic mode experiences strong damping (Fig. 5d) [27]. The second phase transition at p c2 in PST consists of the development of long-range order of antiparallel Pb 2+ displacements and mixed a + bbtilts is revealed by the appearance of additional sets of even-even-odd Bragg peaks and weaker even-odd-odd Bragg reflections observed by single-crystal synchrotron XRD [25].…”

“…All of the characteristic and critical pressures established by the pressure evolution of optical phonon modes and X-ray and neutron diffraction are also marked by changes in the pressure evolution of the adiabatic pseudocubic elastic constants calculated from the acoustic phonon modes [27]. In particular, excellent agreement between the pressure behaviour of the adiabatic as well as the isothemal bulk modulus and that of the average phonon energy of the Pb-O bond stretching optical mode is found, indicating that the overall crystal compressibility is directly related to the mean local compressibility of the PbO 12 cavity [27]. The pressure dependencies of the "soft" mode and the Pb-O bond stretching mode at elevated temperatures show that the first pressure-induced phase transition shifts to lower pressure with temperature increase due to the weakening of the mesoscopic ferroelectric order, while the second pressure-induced phase transition is almost insensitive to temperature changes [28].…”

“…In fact the analysis of  SM (p) reveals that the lowest-energy "soft" mode does not conform to a standard soft-mode behaviour, indicating a significant contribution of order-disorder phenomena to the pressure-induced phase transitions [26]. All of the characteristic and critical pressures established by the pressure evolution of optical phonon modes and X-ray and neutron diffraction are also marked by changes in the pressure evolution of the adiabatic pseudocubic elastic constants calculated from the acoustic phonon modes [27]. In particular, excellent agreement between the pressure behaviour of the adiabatic as well as the isothemal bulk modulus and that of the average phonon energy of the Pb-O bond stretching optical mode is found, indicating that the overall crystal compressibility is directly related to the mean local compressibility of the PbO 12 cavity [27].…”

“…However, temperaturedependent structural studies of A-site doped Pb-based relaxors indicated that the doping-induced local elastic fields as well as disturbance of the system of lone-pair electrons associated with the A-positioned Pb 2+ cations have considerably stronger effects on the relaxor state than local electric fields [3,4]. Recent high-pressure structural studies of PbB' 1/3 B" 2/3 O 3 -type [13][14][15], PbB' 1/2 B" 1/2 O 3 -type relaxors [16][17][18][19][20][21][22][23][24][25][26][27][28], as well as binary (1x)PbB' 1/3 B" 2/3 O 3 -xPbTiO 3 solid solutions [29,30], also emphasized the important role of Pb 2+ local order for the relaxor behaviour and indicated that at ambient conditions antiferrodistortive order coexists with the ferroelectric order on the mesoscopic scale [16][17][18][19][20][21][22][23][24][25][26][27][28][29]. This may turn to be the key structural factor for the remarkable relaxor properties.…”

Brillouin Scattering and its Application in Geosciences

“…Since then, Brillouin scattering has been used to investigate elastic properties and highfrequency viscous behavior of crystalline and amorphous solids (Shapiro et al 1966) liquids, molecular solids and glass-forming compounds, with a special interest in polymers (Patterson 1983;Krüger 1989). The advancement of the technology of Fabry-Perot interferometers then opened new fields of application of this technique, from the study of ferroelectric compounds and their behavior at phase transitions (Jiang and Kojima 2000;Ahart et al 2010;Marquardt et al 2013b), to the investigation of surface and interface vibrational and magnetic excitations of bulk materials and of thin films and multilayers (Wittkowski et al 2002;Milano and Grimsditch 2010). Additional recent applications of Brillouin scattering range from the study of viscoelastic behavior of delicate biomaterials (Speziale et al 2003) to the investigation of the elastic response of nanocomposites (Li Bassi et al 2004), the characterization and design of phononic materials (Cheng et al 2006) to the recent experimental detection of Bose-Einstein condensation of quasiparticles as an effect of external energy pumping (Demokritov et al 2006).…”