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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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]