Synthesis of a polar ordered oxynitride perovskite

Abstract

For decades, numerous attempts have been made to produce polar oxynitride perovskites, where some of the oxygen is replaced by nitrogen, but a polar ordered oxynitride has never been demonstrated. Caracas and Cohen [Appl. Phys. Lett. 91, 092902 (2007)] studied possible ordered polar oxynitrides within density-functional theory (DFT) and found a few candidates that were predicted to be insulating and at least metastable. $\mathrm{YSi}{\mathrm{O}}_{2}\mathrm{N}$ stood out with huge predicted polarization and nonlinear optic coefficients. In this study, we demonstrate the synthesis of perovskite-structured $\mathrm{YSi}{\mathrm{O}}_{2}\mathrm{N}$ by using a combination of a diamond-anvil cell and in situ laser-heating techniques. Subsequent in situ x-ray diffraction, second-harmonic generation, and Raman-scattering measurements confirm that it is polar and a strong nonlinear optical material, with structure and properties similar to those predicted by DFT.