Pyroelectric Effect in Tetragonal Ferroelectrics BaTiO₃ and KNbO₃ Studied with Density Functional Theory

We present a computational methodology for investigating the pyroelectric properties of anharmonic crystalline ferroelectrics. The description of phonon properties and pyroelectricity in perovskite ferroelectrics such as BaTiO₃ and KNbO₃ requires phonon anharmonicity to be taken into account. Our computational approach is based on density functional theory calculations. We use self-consistent phonon theory to describe phonon anharmonicity and to obtain finite-temperature atomic displacements. The Berry phase approach is used to obtain spontaneous polarization needed for the prediction of the primary pyroelectric coefficient. We calculate the fixed-volume primary pyroelectric coefficient and piezoelectric strain secondary pyroelectric coefficient for the tetragonal polymorphs of BaTiO₃ and KNbO₃. We also report the anharmonic phonon dispersions for the studied systems. The computationally relatively straightforward and cost-efficient approach offers a way of screening the pyroelectric coefficients of novel pyroelectric materials for energy harvesting and other microelectronic applications.