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Brillouin spectra of highly-ordered Pb(Sc1/2Ta1/2)O3 (PST-O) and highly-disordered PST (PST-D) were measured over a wide temperature range. The frequency of the longitudinal acoustic (LA) phonon mode of PST-O showed a sharp anomaly corresponding to the sharp maxima of the dielectric permittivity, whereas that of PST-D exhibits a broad anomaly. The remarkable softening of LA phonon was observed below T* = 500 K, which indicates the occurrence of a piezoelectric coupling and/or electrostrictive coupling due to the appearance of non-centrosymmetric polar nanoregions below T*. The relaxation time of the LA phonon of PST-O shows a critical slowing down for order-disorder phase transition, while that of PST-D exhibits a stretched slowing down due to random electric fields related to B-site randomness. [ABSTRACT FROM AUTHOR]

Abstract: CuO‐added 0.96(Na0.5K0.5)(Nb1‐xSbx)O3‐0.04SrTiO3 ceramics sintered at the low temperature of 960°C for 10 hours showed dense microstructures and high relative densities. The specimens with 0.0 ≤  x ≤ 0.04 had orthorhombic‐tetragonal polymorphic phase boundary (PPB) structure. Tetragonal‐pseudocubic PPB structure was observed in specimens with 0.05 ≤  x ≤ 0.07, while the specimen with x = 0.08 has a pseudocubic structure. The structural variation in the specimens is explained by the decreases in the orthorhombic‐tetragonal transition temperature and Curie temperature with the addition of Sb5+ ions. The specimens with 0.05 ≤  x ≤ 0.07, which have tetragonal‐pseudocubic PPB structure, had large electric field‐induced strains of 0.14%‐0.016%. Moreover, these specimens also showed increased d33 values between 280 pC/N and 358 pC/N. In particular, the specimen with x = 0.055 showed particularly enhanced piezoelectric properties: d33 of 358 pC/N, kp of 0.45, and the electric field‐induced strain of 0.16% at 4.5 kV/mm. [ABSTRACT FROM AUTHOR]

Abstract: The origin of the dielectric responses of relaxor ferroelectrics, featured by a signal dispersion according to the measurement frequency, were investigated systematically using a canonical relaxor Pb0.92La0.08(Zr0.65Ti0.35)0.98O3 (PLZT 8/65/35) ceramic. By scanning complex dielectric permittivity over a frequency range from 10 mHz to 10 MHz as a function of temperature from 0°C to 100°C, we revealed that the complex dielectric permittivity spectra obtained from an impedance analyzer are a consequence of a convolution of at least three distinct relaxation processes, featured by the unique relaxation time and distribution. The complex dielectric permittivity spectra at each measurement temperature were deconvoluted by the application of a series of Havriliak‐Negami relaxation models, resulting in three distinguished processes; namely, slow, intermediate, and fast process. We identified that the fast process is responsible for the overall magnitude of capacitance with little influence on the dielectric loss, the intermediate mainly for the thermal evolution of the capacitance, and the slow mainly for the thermal evolution of the loss. With this model, we successfully rationalized the characteristics of the relaxor behavior such as the frequency dispersion of the dielectric maxima, the disparity in peak positions of real and imaginary parts, and the unique feature during aging, so‐called a “dip.” [ABSTRACT FROM AUTHOR]