Piezoelectricity in Lead-Zirconate-Titanate Ceramics – Extrinsic and Intrinsic Contributions

Abstract

Changes in charge density as a response to an external stimuli form basis for numerous applications. Knowing where the atoms are allows numerous deductions to be drawn solely on symmetry arguments. Symmetry essentially dictates what is possible, though typically it does not give absolute values for physical properties. An example is provided by ferroelectrics (Lines & Glass, 1998). Ferroelectrics are a special case of pyroelectric materials, whose properties depend on the spatial scale considered. Single crystals are rather trivial case in which straightforward tensor formulation gives precise description of the physical properties. Obviously, knowledge of single crystal properties is not sufficient, as most materials utilized in applications are polycrystalline. Thus, one must understand how individual crystals are connected and how such a system responds to an external stimulus. This serves as a basis for dividing materials response to an intrinsic and extrinsic contributions. The former is essentially a single crystal response, whereas the latter takes into account the coupling between individual crystals and changes due to the phase transition induced by a stimuli. In practice, the stimuli are stress, heat or electric field. The importance of understanding the intrinsic and extrinsic contributions is not only related to the magnitude but also to the reversibility of the process. Piezoelectric actuators are based on the change in the charge density due to an external stress or change in dimensions by an applied electric field. Very challenging task is to produce a material yielding a reversible response, as the piezoelectric actuators used in atomic force microscopes demonstrate. Activities are ongoing to develop better materials for high precision devices (Hinterstein et al., 2011; Hoffmann & Kungl, 2004). Another topical application is related to the piezoelectric energy harvesting in which a practical way of extracting energy is achievable through the Ericsson energy conversion cycle (Pruvost et al., 2010). Similarly, pyroelectric materials are utilized in infrared radiation detection matrices or pyroelectric energy harvesting components (Olsen & Evans, 1983). In each case it is essential to understand the contribution of grain boundaries, ferroelectric domains within the grains, changes in fractions of different crystal species and the intrinsic contribution within an individual domain. As a further issue one must consider time-dependent phenomena, which reflect the fact that different contributions to polarization 10