First-principles prediction of ferroelectricity in defective wurtzite α-Ga2S3

Wurtzite-type ferroelectrics have attracted much attention as next-generation ferroelectric materials due to their high spontaneous polarizations since the first experimental demonstration of polarization switching for Sc-doped AlN. However, wurtzite-type ferroelectrics require high electric fields to switch their polarization direction, resulting in small margins with breakdown electric fields. To address this issue, considerable efforts have been made to explore wurtzite ferroelectrics with moderate switching barriers. In this study, our first-principles calculations have predicted the ferroelectricity of defective wurtzite α-Ga₂S₃. The calculated polarization is 60 μC cm⁻², which is comparable to or smaller than those of conventional wurtzite ferroelectrics. The minimum energy pathway associated with polarization switching reveals a moderate switching barrier of 67 meV/atom. The energy landscape for α-Ga₂S₃ is quite different from that for its isostructural Al-based counterpart α-Al₂S₃, which our recent theoretical study has predicted to have quadruple-well ferroelectricity. The difference in chemical bonding between cations and sulfide ions accounts for their different energy landscapes for polarization switching.