Determination of the pyroelectric coefficient in spontaneously polarized materials

The pyroelectric coefficient determines the coupling between the spontaneous polarization of a material and changes in the external temperature. While the derivation of this quantity from the definition of the total polarization is straightforward, both measurements and first-principle calculations often disagree on the magnitude of the pyroelectric coefficient. To improve the agreement between experiment and theory we first review the derivation of the pyroelectric coefficient from the modern theory of polarization and then determine the pyroelectric coefficient from a full first-principles calculation. Discrepancies between our calculated temperature dependence and experimental measurement are discussed and analyzed.