Extended contributions to the pyroelectric effect in ferroelectric thin films

Pyroelectric properties of dielectrics have been occupying the agenda of relevant scientific research groups owing to a number of device designs tailoring this effect, such as energy harvesting and caloric devices. Ferroelectrics come forward probably as the most important class of dielectrics in this regard due to their spontaneous polarization that is strongly dependent on temperature as well as strain and electric field. Here, we rigorously formulate and identify the connection between the experimentally accessible pyroelectric coefficient of a perovskite type ferroelectric and contributions arising from strain and clamping conditions. Secondary pyroelectric coefficient under partial clamping reminiscing a thin film is formulated so as to separate it from the primary coefficient that is conventionally defined at constant volume. The formulation is then applied to a number of ferroelectric compositions to reveal the extent of the variations in the secondary pyroelectric effect. The secondary effect reinforces the primary pyroelectric coefficient for the PMN-PT system, whereas it diminishes the total coefficient for PbZr0.4Ti0.6O3 and BaTiO3 systems. The role of thermal expansion coefficients in these variations is discussed.