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Non‐centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which 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 a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second‐order Jahn–Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions 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. [ABSTRACT FROM AUTHOR]

Non‐centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which 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 a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second‐order Jahn–Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions 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. [ABSTRACT FROM AUTHOR]

Non‐centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which 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 a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second‐order Jahn–Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions 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. [ABSTRACT FROM AUTHOR]

Non‐centrosymmetric polar compounds have important technological properties. Reported perovskite oxynitrides show centrosymmetric structures, and for some of them high permittivities have been observed and ascribed to local dipoles induced by partial order of nitride and oxide. Reported here is the first hexagonal perovskite oxynitride BaWON2, which 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 a total order of nitride and oxide at two distinct coordination environments in cubic and hexagonal packed BaX3 layers. A synergetic second‐order Jahn–Teller effect, supported by first principle calculations, anion order, and electrostatic repulsions 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. [ABSTRACT FROM AUTHOR]

Rare earth activated nitridosilicates have important applications as phosphor components in white light emitting diodes. (Oxy)nitridosilicates with β-K 2 SO 4 structure doped with Eu2+ are luminescent materials with emission wavelengths ranging from green to red under excitation with blue-UV light. Here we report the synthesis of isostructural NdEuSiO 3 N and the new oxynitridosilicate NdSrSiO 3 N by solid state reaction between Nd 2 O 3 , NdN, Eu 2 O 3 or SrO and Si 3 N 4 under N 2 /H 2 gas at temperatures of 1300 ​°C and 1500 ​°C respectively. These compounds are the limiting compositions of the solid solution NdSr 1-x Eu x O 3 N crystallizing in the space group Pmnb with cell parameters a ​= ​5.62293(1), b ​= ​7.02285(1) , c ​= ​9.64784(2) Å for NdEuSiO 3 N, and a ​= ​5.63074(9), b ​= ​7.01658(10), c ​= ​9.65765(15) Å for NdSrSiO 3 N. The Nd3+and Eu2+ cations in NdEuSiO 3 N or Nd3+ and Sr2+ in NdSrSiO 3 N show partial order in the two available crystallographic sites of coordination numbers 10 (M1) and 9 (M2), with strongly preferred occupancy of the larger divalent cations Eu2+ (77%) and Sr2+ (78%) for the M1 site, whereas the M2 site is preferred by Nd3+. Magnetic susceptibility measurements down to 2 ​K show that NdEuSiO 3 N is ferromagnetic with T c ​= ​3 ​K, in contrast to NdSrSiO 3 N that shows antiferromagnetic interactions at low temperatures. The band gaps of NdEuSiO 3 N and NdSrSiO 3 N determined from diffuse reflection spectroscopy are 2.37 and 3.72 ​eV respectively. NdEuSiO 3 N and the members of the solid solution NdSr 0.98 Eu 0.02 SiO 3 N and NdSr 0.5 Eu 0.5 SiO 3 N are orange-red light emitting luminescent materials, showing a broad emission band centered between 605 and 639 ​nm under excitation at 405 ​nm. These compounds are new phosphor materials with emission wavelengths shifted to the red with respect to the isostructural oxysilicates, which is induced by the introduction of nitride. β-K 2 SO 4 type NdEuSiO 3 N and the new oxynitridosilicate host NdSrSiO 3 N activated with Eu2+ show orange-red luminescence under excitation at 405 ​nm. [Display omitted] • Synthesis of the new oxynitridosilicate NdSrSiO 3 N and the solid solution NdSr 1-x Eu x SiO 3 N (0 ​≤ ​x ​≤ ​1) with β-K 2 SO 4 structure. • -Nd3+ ions preferentially occupy the 9th-coordinated sites whereas Sr2+ and/or Eu2+ prefer the 10th-coordinated sites. • NdEuSiO 3 N is ferromagnetic below 3 ​K whereas NdSrSiO 3 N shows antiferromagnetic correlations at low temperature. • NdEuSiO 3 N and NdSrSiO 3 N:Eu compounds are orange-red luminescent materials under excitation at 405 ​nm. [ABSTRACT FROM AUTHOR]