Prediction of New Ferroelectric Clathrate and Polar Oxynitrides

We predict using DFT a new ferroelectric clathrate with composition ScB3C3, which exhibits high polarization density and low mass density (PRL 125, 127601, 2020). Molecular dynamics simulations show spontaneous polarization with a Tc of ∼370 K. We have also simulated a variety of oxynitrides as functions of pressure and epitaxial strain (arXiv:2008.06582). We find that the P4mm perovskite structures of YGeO2N, LaSiO2N, and LaGeO2N are dynamically stable at zero pressure, and thus should be synthesizable by pulsed laser deposition or other atomic layer deposition methods. In addition we find that ferroelectric polar phases of perovskite-structured oxynitrides can be thermodynamically stable and synthesized at high pressure on appropriate substrates.