WEB Electric field induced structural behaviour of barium titanate with different grain sizes
Functional ceramics are part of our daily life: whether as microelectronics, sensors or actuators. Barium titanate (BT) is a classic ferroelectric material and is indispensable in dielectric applications. Additionally, BT exhibits excellent electromechanical properties with a large electric field induced strain. The fundamental mechanisms behind the electromechanical behaviour are still not fully understood, and for a continuous miniaturization of dielectric devices, the grain size has to be reduced. It is therefore essential to understand the correlation of the grain size with the dielectric and electromechanical properties. In this work, the influence of the grain size distribution in dense BT on the piezoelectric response was investigated. Several different approaches were used to achieve a broad range of grain sizes. These include BT powder grinding at sub micrometric levels in a planetary mill with zirconia spheres. Two steps sintering in which the sample is subjected to a high sintering temperature for a short period of time and then a long time at a low sintering temperature, thus obtaining a dense structure with medium grain sizes. Quenched sintering in which the sample is subjected to a high sintering temperature with subsequent rapid cooling, being possible to partially avoid the abnormal growth of the grains. And also, hot isostatic pressing at a pressure of 1500 bar at 1100 °C, densifying the sample to a level where there is no grain growth. As a result, the grain sizes vary over three orders of magnitude. The microstructure was characterized using electron microscopy in order to determine the average grain size. The electromechanical behaviour was characterized using a commercial system equipped with an interferometer to measure the polarisation and strain hysteresis. The response of the crystal structure to an applied electric field was determined with in situ synchrotron diffraction. Our results show that the electromechanical behaviour varies substantially with varying grain size. A sophisticated texture analysis using the STRAP method  allows to understand the electric field induced response. The results show a behaviour that deviates from that previously described in the literature.