  For decades, numerous attempts have been made to produce polar oxynitride
perovskites, where some of the oxygen are replaced by nitrogen, but a polar
ordered oxynitride has never been demonstrated. Caracas and Cohen 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. YSiO2N stood out with huge predicted polarization and nonlinear
optic coefficients. In this study, we demonstrate the synthesis of
perovskite-structured YSiO2N by using a combination of a diamond anvil cell and
in-situ laser heating technique. 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.
