We describe measurements of the pyroelectric coefficient of epitaxial layers of Ba0.6Sr0.4TiO3 (BST) and PbZr0.2Ti0.8O3 (PZT) using a modulated laser as the heat source in the frequency range 1 Hz to 10 MHz. The pyroelectric coefficient is also measured as a function of applied static electric field and for films grown on SrTiO3, DyScO3, and GdScO3 substrates. The heat diffusion equation is solved in cylindrical coordinates for the temperature field in a multilayer sample heated by a Gaussian-shaped laser beam. The secondary contribution to the pyroelectric effect caused by piezoelectric effects and in-plane thermal expansion is revealed by the difference between the pyroelectric coefficients at high and low frequencies. The secondary pyroelectric effect has the same dependence on applied field as the pyroelectric coefficient. The magnitude of the secondary effect changes with heating frequency because of changing mechanical conditions, but the pyroelectric coefficient has no other frequency dependence between 1 Hz and 10 MHz. The secondary effect is approximately 15% and 20% of the total pyroelectric response for PZT and BST films, respectively.

We report laser-based direct measurements of the pyroelectric and electrocaloric effects of PbZr1-xTixO3 epitaxial layers as a function of temperature and electric field. By evaluating the differences between the total pyroelectric and electrocaloric coefficients, we determine the secondary contribution to the electrocaloric effect that is created by a combination of piezoelectric and elastocaloric effects. The secondary contribution to the electrocaloric coefficient has the opposite sign as the primary effect and therefore reduces the overall entropy change of PbZr1-xTixO3 in an electric field. The absolute magnitude of the secondary effect is comparable to the primary effect at elevated temperatures of ≈200°C.