A first-principles view of pyroelectricity

The pyroelectric effect is the response of the spontaneous polarization with respect to the temperature fluctuation. It impacts a wide range of applications. Pyroelectricity arises from the primary effect (at constant external strain) and the secondary effect (thermal expansion alters piezoelectric polarization). Here a computational route from first principles is developed. Calculations are made for the pyroelectric coefficients of wurtzite GaN and ZnO. An excellent agreement with experimental data is found. In these bulk materials, we reveal the crucial role of the primary pyroelectricity arising from the electronic redistribution induced by atomic thermal vibrations. For 2D materials, we demonstrate out-of-plane pyroelectricity in the recently synthesized Janus MoSSe monolayer and in-plane pyroelectricity in the theoretically stable group-IV monochalcogenide GeS monolayer. For GeS monolayer, it is notable that the secondary pyroelectricity is significant, and hence applying strains can dramatically tune its intrinsic pyroelectricity.