First-principles study of pyroelectricity in GaN and ZnO

TL;DR

This study uses first-principles calculations to analyze the primary pyroelectric coefficients of GaN and ZnO, revealing the thermal shifts of internal strains as the main cause of pyroelectricity and the temperature-dependent dominance of primary and secondary effects.

Contribution

It provides a detailed first-principles analysis of pyroelectricity in GaN and ZnO, highlighting the roles of internal strains and phonon modes across temperatures.

Findings

Primary pyroelectricity dominates at low temperatures.

Secondary pyroelectricity becomes significant at high temperatures.

Phonon contributions are moderately described by Debye and Einstein models.

Abstract

First-principles calculations are made for the primary pyroelectric coefficients of wurtzite GaN and ZnO. The pyroelectricity is attributed to the quasiharmonic thermal shifts of internal strains (internal displacements of cations and anions carrying their Born effective charges). The primary (zero-external-strain) pyroelectricity dominates at low temperatures, while the secondary pyroelectricity (the correction from external thermal strains) becomes comparable with the primary pyroelectricity at high temperatures. Contributions from the acoustic and the optical phonon modes to the primary pyroelectric coefficient are only moderately well described by the corresponding Debye function and Einstein function respectively.