Previous studies of unstable ('soft') optical modes in ferroelectrics have reported minimum frequencies of 1 cm(-1) (30 GHz) for underdamped phonons. In this work we fabricate a cylindrical coaxial specimen and rectangular plate waveguide specimens of tris-sarcosine calcium chloride (TSCC) and follow its soft mode several orders of magnitude lower to 1 GHz. Below 30 GHz the relaxation time is probably characteristic of domain wall motion; the new theory of Pakhomov et al (2013 Ferroelectrics at press) predicts 0.5 THz far from TC and a (T - T(C))/T(C) dependence, in agreement with our experimental values. This discovery has implications for GHz electronics such as phased array radar or other voltage-tunable low-loss components. The mean-field frequency description of the soft mode response f(T) is supported via precision calorimetry on TSCC with and without Br-doping. The ferroelectric-antiferroelectric phase transition, previously suggested from high-pressure data, is confirmed at 45 K at 1 atm.

Complex dielectric properties of Pb(Fe1/2Nb1/2)O3 ceramics were investigated in a broad frequency range from 100 Hz up to 90 THz. A broad dielectric anomaly was observed near the temperature of the ferroelectric phase transition (TC1 = 376 K). Below 1 MHz, the anomaly is strongly influenced by conductivity of the sample, but higher frequency data taken up to 81 MHz reveal a broad and frequency independent peak at TC1 typical for a diffuse ferroelectric phase transition. Surprisingly, dielectric permittivity measured at 37 GHz exhibits a peak shifted by 25 K above TC1, which indicates polar nanoregions with dynamics in microwave frequency region. A dielectric relaxation, which appears in THz region below 700 K, slows down towards TC1 and again hardens below TC2 = 356 K. This central mode drives both phase transitions, so they belong to order–disorder type, although the polar phonons exhibit anomalies near both phase transitions. In the paraelectric phase, infrared reflectivity spectra correspond to local Fm3¯m structure due to short-range chemical ordering of Fe and Nb cations on the B perovskite sites. Moreover, each polar phonon is split due to two different cations on the B sites. Recently, Manley et al. [Nat. Commun. 5, 3683 (2014)] proposed a new mechanism of creation of polar nanoregions in relaxor ferroelectrics. They argued, based on their inelastic neutron scattering studies of PMN–PT, that the TO1 phonon is split and interaction of both components gives rise to so called Anderson phonon localization, which can produce regions of trapped standing waves and these waves induce polar nanoregions in relaxors. We cannot exclude or confirm this mechanism, but we show that the splitting of polar phonons is a common feature for all complex perovskites with relaxor ferroelectric behavior and it can be also observed in canonical ferroelectric BaTiO3, where the soft mode is split in paraelectric phase due to a strong lattice anharmonicity.

Perpetual demand for higher transfer speed and ever increasing miniaturization of radio and microwave telecommunication devices demands new materials with high electrical tunability. We have investigated built in electrical and strain fields' influence on the electrical tunability in Ba0.7Sr0.3TiO3 thin film hetero-system grown by pulsed laser deposition technique. We observed the built in electrical field by local piezo-force microscopy (as deflected hysteresis loops) and macroscopic impedance analysis (as asymmetric tunability curves), with the calculated 88 kV/cm built in field at room temperature. Negative −1.4% misfit strain (due to clamping by the substrate) enhanced ferroelectric phase transition temperature in Ba0.7Sr0.3TiO3 thin film by more than 300 K. Built in fields do not deteriorate functional film properties—dielectric permittivity and tunability are comparable to the best to date values observed in Ba1−xSrxTiO3 thin films.

This paper presents a systematic investigation of the electric properties of epitaxial PMN-33PT thin film as a function of temperature and frequency. Complex impedance measurements were performed over the temperature range of 30 -500 K and frequency range 20 Hz -1 MHz. Obtained results were corrected for the SRO series resistance. Ferroelectric hysteresis loops and electric field tunability of the real part of dielectric permittivity were measured in the 300 K -450 K temperature range and at a frequency of 1 kHz. The results of electrical field tunability of complex dielectric permittivity were approximated by Landau-Ginsburg-Devonshire theory frame by the Johnson relation. Meanwhile, ferroelectric hysteresis loop measurements of epitaxial PMN-33PT thin film shows a good hysteresis property with a remnant polarization of 2P r 10 mC/cm 2 and coercive field of 2E c 12 kV/cm at temperature range from 300 K to 380 K.

Thin epitaxial films have a great potential to be used in real life applications, such as oxide-on-silicon. However, they often contain a large amount of defects, leading to an enhanced electrical conductivity. This could be desirable in some applications (i. e. memristors), but the mechanism is not fully understood. Here we report on the investigation of epitaxial barium strontium titanate thin films deposited on strontium titanate single crystal substrates (Ba 0.7 Sr 0.3 TiO 3 /SrRuO 3 //SrTiO 3 heterostructures) with a controlled epitaxial strain. The impedance analysis allowed us to propose a model, which explains changes in the temperature dependence of the conductivity based on the strain-dependent anisotropic change of electron/hole mobility.