Lattice dynamics and ferroelectric properties of the nitride perovskite ${\mathrm{L}\mathrm{a}\mathrm{W}\mathrm{N}}_3$

Using first-principles calculations we examine the crystal structures and phase transitions of nitride perovskite LaWN${}_3$. Lattice dynamics calculations indicate that the ground-state structure belongs to space group $R3c$. Two competitive phase transition pathways are identified which are characterized by symmetry-adapted distortion modes. The results suggest that $R3c$ LaWN${}_3$ should be an excellent ferroelectric semiconductor: its large spontaneous polarization of around 61 $\mu$C/cm${}^2$ is comparable to that of PbTiO${}_3$, and its band gap is about 1.72 eV. Ferroelectricity is found to result from the \emph{B}-site instability driven by hybridization between W-5$d$ and N-2$p$ orbitals. These properties make LaWN${}_3$ an attractive candidate material for use in ferroelectric memory devices and photovoltaic cells.