Angewandte Chemie, Accepted Article.
Non‐centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures and for some of them high permittivities have been observed, ascribed to local dipoles induced by partial order of nitride and oxide. Here we report the first hexagonal perovskite oxynitride BaWON2, that shows a polar 6H polytype. Synchrotron X‐ray and neutron powder diffraction, and annular bright‐field in scanning transmission electron microscopy indicate that it crystalizes in the non‐centrosymmetric space group P63mc, with total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. Synergetic second order Jahn‐Teller effect supported by first principle calculations, anion order and electrostatic repulsion between W6+ cations induce large distortions at two inequivalent face sharing octahedra that lead to long‐range ordered dipoles and spontaneous polarization along the c axis. The new oxynitride is a semiconductor with a band gap of 1.1 eV and a large permittivity.