Electronic structures and ferroelectric properties of LaWN₃ ultrathin films

Nitride perovskites have received much less attention compared to oxide and halide perovskites. It is fundamentally important to investigate the physical properties of nitride perovskites from both scientific and technological perspectives. In this study, using lanthanum tungsten nitride (LaWN₃) as a prototype, we investigated the electronic and ferroelectric properties of nitride perovskites ultrathin films using the density-functional theory method. We observed an abnormal quantum confinement effect in LaWN₃ ultrathin films. We also found that LaWN₃ ultrathin films exhibit robust ferroelectricity, with ferroelectric polarization scaling well with film thickness. The thinnest film shows a different stabilization mechanism for the ferroelectric state compared to the bulk, where ferroelectricity is primarily induced by the hybridization between W-5d and N-2p orbitals. Comparisons of the physical properties of nitride perovskites with those of oxide and halide perovskites provide new insights into understanding the general rules governing the properties of two-dimensional perovskites.