We have studied an incipient ferroelectric BaZrO 3 single crystal with perovskite structure by terahertz time-domain and Raman scattering spectroscopies. The phonon-polariton dispersion relation of the lowfrequency infrared active TO1 and TO2 modes was studied from the real and imaginary parts of the complex dielectric constants at 8 K. The experimentally observed complex polariton dispersion relations are discussed by a damped harmonic oscillator model. First-order Raman active modes, forbidden in cubic Pm3m symmetry, have been observed in a BaZrO 3 single crystal, indicating the lowering of cubic symmetry.

First principles calculations of structural, electronic, mechanical, and thermodynamic properties of different polymorphs of BiVO 4 are performed using Bender-type plane/wave ultrasoft pseudopotentials within the generalized gradient approximation (GGA) in the frame of density functional theory (DFT). The calculated structural and electronic properties are consistent with the previous theoretical and experimental results. The electronic structures reveal that m-BiVO 4 , op-BiVO 4 , and st-BiVO 4 have indirect band gaps, on the other hand, zt-BiVO 4 has a direct band gap. From the DOS and Mulliken's charge analysis, it is observed that only m-BiVO 4 has 6s 2 Bi lone pair. Bond population analysis indicates that st-BiVO 4 shows a more ionic nature and a similar result is obtained from the elastic properties. From the elastic properties, it is observed that st-BiVO 4 is more mechanically stable than the others. st-BiVO 4 is more ductile and useful for high electro-optical and electro-mechanical coupling devices. Our calculated thermodynamic properties confirm the similar characteristics found from electronic and elastic properties. m-BiVO 4 is useful as photocatalysts, solid state electrolyte, and electrode and other polymorphs are applicable in electronic device fabrications.

The elastic properties of uniaxial relaxor SrxBa1−xNb2O6 (x = 0.70, SBN70) single crystals with strong random fields (RFs) were studied by Brillouin scattering spectroscopy as functions of temperature and external electric field along the [001] direction. A remarkable diffuseness of a ferroelectric phase transition was observed both on zero field heating and zero field cooling. The analysis of elastic anomaly shows the stretched critical slowing down of polar nanoregions (PNRs). Under 3.0 kV/cm, a complete alignment of nanodomains and an enhancement of the long-range ferroelectric order were observed below the Curie temperature TC = 23 °C. The alignment of quasistatic PNRs above TC was also observed under a sufficiently strong electric field. In a field-dependent measurement, a mixed state consisting of field-induced macrodomains and nanodomains caused by RFs was observed at 3.4 kV/cm. This mixed state persisted up to 9.0 kV/cm due to the incomplete switching of nanodomains to the macro/single domain state.

Relaxor ferroelectric 0.83Pb(Mg1/3Nb2/3)O3–0.17PbTiO3 (PMN–17PT) single crystals were studied by Brillouin scattering to investigate the role of polar nanoregions (PNRs) with intermediate random fields (RFs). Upon cooling, the central peak began to appear at the Burns temperature (TB) of ∼600 K, indicating the existence of polarization relaxations induced by PNRs. The fitting performed using the equation of stretched slowing down at the inverse relaxation time revealed that the slowing down of PNRs was suppressed in PMN–17PT compared with that in PMN–56PT owing to the increase in the strength of RFs. At room temperature, the splitting of the longitudinal acoustic mode at 1.6 kV/cm was observed owing to the coexistence of the macrodomain formed by the external electric field along the [100] axis and the nanodomains formed by RFs. The appearance of the transverse acoustic mode at 3.2 kV/cm indicates the field-induced rhombohedral-to-tetragonal phase.