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Transition metal perovskite oxynitrides are emergent materials for applications as visible light-active photocatalysts for water splitting and CO2 reduction and as thermoelectric, dielectric, and magnetic materials. They have been reported for early transition metals Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W in the B sites and alkaline earth or rare earth metals in the A sites. Nitrogen is less electronegative and more polarizable than oxygen, and nitride is more charged than oxide. As a consequence, the introduction of nitride in an oxidic perovskite has important effects on the covalency of bonds, the energy of electronic levels, and the valence states of the cations. This work discusses fundamental and recent developments of perovskite oxynitrides of transition metals of groups 4, 5, and 6 as photocatalytic and electronic materials, focusing on the important aspects of synthetic methodologies, crystal structures, and anion ordering, in connection with the observed physical and chemical properties. Some examples of compounds with late transition metals and complex structures such as layered and double perovskites are also discussed. [ABSTRACT FROM AUTHOR]

RHfO2N perovskites with R = La, Nd and Sm show a GdFeO3-type structure and are semiconductors with band gaps of 3.35, 3.40 and 2.85 eV and relative dielectric constants of 30, 16 and 28 respectively. These compounds have adequate reduction and oxidation potentials to conduct the overall water splitting reaction, and the analogous perovskite LaZrO2N with a band gap of 2.8 eV shows photocatalytic activity under visible light irradiation for O2 evolution. [ABSTRACT FROM AUTHOR]

LnCrO3−xNx perovskites with Ln = La, Pr and Nd and nitrogen contents up to x = 0.59 have been synthesised through ammonolysis of LnCrO4 precursors. These new materials represent one of the few examples of chromium oxynitrides. Hole-doping through O2−/N3− anion substitution suppresses the magnetic transition far less drastically than Ln3+/M2+ (M = Ca, Sr) cation substitutions because of the greater covalency of metal–nitride bonds. Hence, nitride-doping is a more benign method for doping metal oxides without suppressing electronic transitions. [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]