Lattice dynamics and ferroelectric properties of the nitride perovskite LaWN3

Using first-principles calculations we examine the crystal structures and phase transitions of nitride perovskite LaWN3. 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 R3cLaWN3 should be an excellent ferroelectric semiconductor, as its large spontaneous polarization of around 61 μC/cm2 is comparable to that of PbTiO3, and its band gap is about 1.72 eV. Ferroelectricity is found to result from the B-site instability driven by hybridization between W-5d and N-2p orbitals. These properties make LaWN3 an attractive candidate material for use in ferroelectric memory devices and photovoltaic cells.