Search

The piezotronic effect gained considerable interest during the last decade. It utilizes the interaction of stress-induced piezoelectric charges and the electronic band structure in piezoelectric semiconductors. This could lead to new applications like strain-triggered transistors or transparent strain/stress sensors. Apart from single Schottky barriers, double Schottky barriers in varistor boundaries in ZnO can be modified extensively by the application of stress. The gauge factors obtained by this method far exceed values for commercial strain sensors. The determination of the underlying physical mechanisms is therefore of utmost importance for applications in strain sensing. In this work, the experimental results of the influence of mechanical stress on the current–voltage characteristics of ZnO-based varistor ceramics are contrasted to simulations. It is verified that a recently introduced simplified physical model based on parallel conductive regions is capable of explaining the stress sensitivity of varistor ceramics and the evolution of the gauge factor as a function of mechanical stress. At electric fields below the breakdown voltage, small percolating pathways through the microstructure determine the current response of the ceramic. This current localization effect becomes even more pronounced when the material is mechanically stressed with an externally applied uniaxial compressive load. Considering application in stress sensors, current localization in the material could possibly lead to local heating effects and degradation of the material.

The electrocaloric (EC) effect in a BaTiO3 single crystal oriented along the [001] direction has been studied by direct high-resolution EC measurements in the vicinity of the field-induced critical point. It is shown that the observed behavior of the EC temperature change , as well as the heat capacity anomalies are in good agreement with the predictions of the Landau theory. We also present the electric field-temperature phase diagram for the field-induced paraelectric-to-ferroelectric phase transition line, derived from the calculated latent heat.

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.

The ferroelectric transition line in the electric-field temperature phase diagram of the canonical relaxor ferroelectric ceramics 9/65/35 PLZT has been studied via polarization and high-resolution heat capacity measurements. The modified calorimetric relaxation measurements show a change of the sample temperature if the applied electric field is sufficiently high to induce a ferroelectric transition. The anomaly in the sample temperature is a consequence of the released excess heat, i.e., latent heat at the transition from the disordered dipolar glass state to the long-range–ordered ferroelectric state. The presence of latent heat supports the well-established physical picture of relaxors according to the so-called dipolar glass scenario. Furthermore, it was found that latent heat decreases with increasing temperature, indicating the existence of a diffuse-type critical point.