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.

Transition metal perovskite oxides are of permanent interest because they show innumerable important properties and applications. Their chemical diversity may be expanded by modifying the anion composition with the introduction of nitride that shows electronic and crystal chemical characteristics close to oxide.1 Nitrogen is less electronegative and more polarizable than oxygen, and nitride is more charged than oxide. These crucial differences between the two anions are the important factors affecting the chemical and physical properties of perovskite oxynitrides ABO3−xNx (A = alkaline earth or rare earth metal; B = transition metal). They have been investigated for several important applications, more intensively as water splitting photocatalysts active under visible light for hydrogen generation2 and as materials with high dielectric constants.3 Perovskite oxynitrides also show remarkable applications as non-toxic pigments4 and as thermoelectric,5 magnetic,6 and ferroelectric materials.7,8

When substituting oxide in a semiconductor, nitride introduces 2p states at the top of the valence band, decreasing the bandgap and affecting, for instance, the photocatalytic activity that shifts to the visible light.9 The higher charge of N3− increases the ionic polarizability and the dielectric constant. The possibility of formation of permanent electric dipoles8 is affected by the order of the two anions,10–13 which also has an impact on the bandgap14 and other relevant properties. To compensate the −3 charge of nitride, the oxidation states of the transition metals have to be high. They should be stable in the reducing conditions under NH3 or at high temperatures under N2 flow that are used for the synthesis of oxynitrides. These two requirements have directed the majority of explored compositions of perovskite oxynitrides to early transition metals from groups 4, 5, and 6, which have stable high valence states and show relative low electronegativities.

The most common method for the synthesis of perovskite oxynitrides is ammonolysis of ternary oxide precursors.15,16 The direct solid state reaction under NH3 between individual metal oxides or salts has been used for perovskites containing alkaline earth cations, and also high temperature reactions between nitrides, oxynitrides, and oxides under N2 have been performed.17 

Research in perovskite oxynitrides was initiated in the 1970s by Marchand and co-workers, who reported the first example of layered Nd2AlO3N18 with K2NiF4-type structure and, later, the alkaline earth tantalum and niobium perovskites BaTaO2N, BaNbO2N, SrTaO2N, and CaTaO2N.15,19 The interest in the field was stimulated in 2000 with the publication in Nature by Jansen and Letschert4 of new non-toxic red-yellow pigments in the solid solution Ca1−xLaxTaO2−xN1+x and, later, with other early reports from different groups of new compounds with additional applications.3,20–22 Research during the first decade after these initial reports was reviewed by Ebbinghaus et al. in 201023 and Fuertes in 2012.24 This perspective aims at giving a present overview of the reported compounds in the three groups of transition metals, identifying new challenges, and focusing on relevant aspects and progress in the synthesis pathways, important structural features such as anion order, and chemical and physical properties.

Within the group 4, the titanium compounds are the most investigated because of their photocatalytic activity and dielectric properties. LaTiO2N and NdTiO2N were first prepared by Marchand et al. by ammonolysis at 900 °C of Ln2Ti2O7 (Ln = La, Nd).25 For Ln = La, another method treating this oxide and urea under N2 has also been suggested.26 The crystal structure of the lanthanum compound was initially reported to be triclinic I-117 from the refinement of neutron powder diffraction data. Further investigation on a highly crystalline sample prepared by a flux method indicated the orthorhombic symmetry Imma, using electron diffraction and refinement from synchrotron and neutron powder diffraction data.27 The distribution of nitride and oxide was found totally disordered in the two studies, and more recently as partially ordered28 with occupancies in agreement with a cis configuration of nitrides as suggested for SrTaO2N, SrNbO2N, and other perovskite oxynitrides11,29,30 (Fig. 1). Recent density functional theory (DFT) calculations have indicated that whereas a N-cis configuration is more stable in bulk LaTiO2N, a non-polar trans arrangement of nitrides is preferred at the (001) surface of this perovskite.31 

FIG. 1.

Crystal structure of the perovskite SrTaO2N29 projected along (a) [001] and (b) [010] directions of the superstructure 2ap × 2ap × 2ap of the perovskite subcell (of parameter ap) showing N/O occupancies determined by neutron diffraction. Oxygen, nitrogen, strontium, and tantalum atoms are represented as white, black, golden, and blue spheres, respectively. SrTaO2N has an apparent I4/mcm space group at room temperature because of tilting, but N/O order lowers the tetragonal symmetry to Fmmm. (c) N/O order in ABO2N perovskite oxynitrides showing disordered cis N-M-N zig-zag chains (blue line) confined in planes.11 

FIG. 1.

Crystal structure of the perovskite SrTaO2N29 projected along (a) [001] and (b) [010] directions of the superstructure 2ap × 2ap × 2ap of the perovskite subcell (of parameter ap) showing N/O occupancies determined by neutron diffraction. Oxygen, nitrogen, strontium, and tantalum atoms are represented as white, black, golden, and blue spheres, respectively. SrTaO2N has an apparent I4/mcm space group at room temperature because of tilting, but N/O order lowers the tetragonal symmetry to Fmmm. (c) N/O order in ABO2N perovskite oxynitrides showing disordered cis N-M-N zig-zag chains (blue line) confined in planes.11 

Close modal

LaTiO2N with a bandgap of 2.1 eV and an absorption edge of 600 nm is one of the most studied perovskite oxynitrides since the first report by Domen et al. on its ability to split water under visible light in the presence of sacrificial agents.32–34 It showed a low apparent quantum yield that was improved significantly using CoOx as co-catalyst.35,36 The photocatalytic activity improved in samples obtained by treatment of La2Ti2O7 crystals in NH3 using different fluxes.37 LaTiO2N is also active as photocatalyst under visible light for the reduction of CO2 into CH4 in the presence of H2O.38 As a dielectric material, it has been investigated in the form of ceramics and thin films. The films were grown by radio frequency reactive magnetron sputtering on Pt/Si/SiO2/Si39 or Nb:SrTiO340 substrates using LaTiO2N or La2Ti2O7 targets, respectively. The measured dielectric constant εr was 750 for a ceramic sample,28 whereas it was 325 for a thin film deposited on Nb–SrTiO3.40 

Highly sintered ceramics of this perovskite cannot be obtained because it decomposes completely at 1100 °C under N2 into a mixture of LaTiO3, La2O3, and TiN.41 Using DFT calculations, spontaneous polarization has been predicted in thin films, induced by epitaxial strain on the anion order.42 

The compounds LnTiO2N with Ln = Nd, Ce, Pr,43,44 and Eu45 have also been also investigated for their photocatalytic and electronic properties. The four oxynitrides show the orthorhombic GdFeO3-type structure with tilting system a+bb and space group Pnma, with a disordered distribution of nitride and oxide.22,43 In the Ce and Pr compounds, short range anion order has been suggested from electron diffraction experiments. NdTiO2N, CeTiO2N, and PrTiO2N show bandgaps in the range of 2.0–2.1 eV, close to LaTiO2N. The photocatalytic activity in water oxidation of NdTiO2N in the presence of a sacrificial agent is similar to that of the lanthanum compound. However, the Pr and Ce compounds show lower activities, which is ascribed to the presence of localized f-orbital states in the bandgap or near the valence band maximum that act as electron–hole recombination centers.44 EuTiO2N can be prepared from the oxyhydride EuTiO2.82H0.18 by H/N3− exchange under NH3.45 Magnetic measurements indicate that in this oxynitride europium shows the oxidation state +3, in contrast with perovskites of other early transition metals such as Eu+2TaO2N, Eu+2NbO2N,6 and Eu+2WON2.46 A similar H/N3− topochemical exchange synthetic approach has been used to introduce nitride in the perovskites BaTiO3 and SrTiO3.7 Ferroelectric BaTiO2.4N0.4 has been prepared by ammonolysis of BaTiO3−xHx, and oxy-hydride-nitrides have been obtained as intermediate products starting either with BaTiO3−xHx or SrTiO3−xHx.

LaZrO2N was prepared for the first time by ammonolysis of amorphous La2Zr2O7 during several weeks at 950 °C.22 The same perovskite has been more recently synthesized in N2 by reaction between La2O3, ZrN, and ZrO2 at 1500 °C during 25 h.47 Zirconium perovskites of smaller rare earths such as Pr, Nd, and Sm could not be prepared by similar synthesis methods, but they can be accessed under 2–3 GPa pressure at 1200–1500 °C starting with a mixture of Zr2N2O and Ln2O3.48 All zirconium rare earth perovskites adopt the distorted GdFeO3-type structure, and a total disorder of anions has been reported for LaZrO2N. The isostructural LnHfO2N compounds with Ln = La, Pr, and Sm are prepared at room pressure at 1500 °C treating a mixture of Hf2N2O and Ln2O3 for 3 h.47 As reported for LaZrO2N, a totally disordered distribution of N and O has been found from Rietveld refinement of neutron powder diffraction data. LaZrO2N, LaHfO2N, PrHfO2N, and SmHfO2N are semiconductors with bandgaps of 2.80 eV, 3.35 eV, 3.40 eV, and 2.85 eV, respectively, determined from diffuse reflectance spectroscopy [Fig. 2(a)]. 49 These are reduced by 2 eV or more with respect to the oxidic perovskites SrHfO3, BaHfO3, or BaZrO3 that show bandgaps of 5.7 eV, 5.8 eV, and 5 eV, respectively, and are larger by 0.7 eV or more as compared to LaTiO2N. The bandgap increase in LnBO2N (Ln = lanthanide) perovskites within the 4 group of transition metals from 3d to 5d row is due to the increased potential of the empty d orbitals that mainly contribute to the conduction bands. The Zr and Hf compounds show photocatalytic activity in water oxidation or reduction in the presence of co-catalysts. LaHfO2N and NdHfO2N have adequate reduction and oxidation potentials to perform the overall water splitting reaction, and LaZrO2N has the ability to oxidize water under visible light although it undergoes self-oxidative decomposition evolving N247 [Fig. 2(b)]. In contrast with LaTiO2N, the measured dielectric constants of zirconium and hafnium perovskite oxynitrides are relatively low. At room temperature, εr was 30 for LaZrO2N and LaHfO2N, 16 for NdHfO2N, and 28 for SmHfO2N (Fig. 3). These values are similar to those for the oxidic perovskites BaHfO3, SrHfO3, and CaHfO3r = 24.2, 23.5, and 21.4, respectively) and suggest potential applications of these oxynitrides in memory capacitors.50 

FIG. 2.

(a) Diffuse reflectance spectra, bandgaps determined using the Kubelka–Munk function, and powder photographs of LaHfO2N, NdHfO2N, SmHfO2N, and LaZrO2N.49 (b) Time courses of H2 or O2 evolution from aqueous methanol solution or aqueous AgNO3 solution, respectively, on (a) LaHfO2N, (b) NdHfO2N, and (c) LaZrO2N sample under light irradiation (λ > 300 nm for LnHfO2N samples or λ > 400 nm for LaZrO2N). (a) and (b) are adapted and reproduced with permission from Black et al., Chem. Commun. 54, 1525 (2018). Copyright 2018 Royal Society of Chemistry.

FIG. 2.

(a) Diffuse reflectance spectra, bandgaps determined using the Kubelka–Munk function, and powder photographs of LaHfO2N, NdHfO2N, SmHfO2N, and LaZrO2N.49 (b) Time courses of H2 or O2 evolution from aqueous methanol solution or aqueous AgNO3 solution, respectively, on (a) LaHfO2N, (b) NdHfO2N, and (c) LaZrO2N sample under light irradiation (λ > 300 nm for LnHfO2N samples or λ > 400 nm for LaZrO2N). (a) and (b) are adapted and reproduced with permission from Black et al., Chem. Commun. 54, 1525 (2018). Copyright 2018 Royal Society of Chemistry.

Close modal
FIG. 3.

Temperature dependence of dielectric permittivities of (a) LaHfO2N, (b) NdHfO2N, (c) SmHfO2N, and (d) LaZrO2N measured at 100 kHz. Reproduced with permission from Black et al., Chem. Commun. 54, 1525 (2018). Copyright 2018 Royal Society of Chemistry.

FIG. 3.

Temperature dependence of dielectric permittivities of (a) LaHfO2N, (b) NdHfO2N, (c) SmHfO2N, and (d) LaZrO2N measured at 100 kHz. Reproduced with permission from Black et al., Chem. Commun. 54, 1525 (2018). Copyright 2018 Royal Society of Chemistry.

Close modal

Vanadium oxynitride perovskites have been investigated for their electrical and magnetic properties. LaVO3−xNx samples (0 < x < 0.9) were first prepared by Marchand et al. by treatment of LaVO4 under NH3,51 and perovskites of Pr and Nd were further synthesized using a similar synthetic approach.30,52 The nitridation of LnVO4 compounds proceeds through a first step of reduction to LaVO3 followed by the incorporation of nitride in this perovskite with concomitant oxidation of V3+ to V4+. LnVO3−xNx (Ln = La, Pr, Nd) with x up to 1 show the GdFeO3 type structure at room temperature. NdVO2N and PrVO2.24N0.76 with vanadium in d1 and d1/d2 configurations, respectively, show partial anion order consistent with cis-VN2 chains similarly to perovskite oxynitrides of d0 transition metals, indicating that this distribution is robust to electron doping and to the disorder created by non-stoichiometry. LaVO2.09N0.91 and PrVO2.24N0.76 show spin freezing transitions at low temperatures, and NdVO2N is paramagnetic. Epitaxial thin films of LaVO3−xNx have been grown by plasma-assisted pulsed laser deposition.53 They are highly crystalline and electrically insulating which is suggested to be a consequence of carrier localization induced by anion disorder.

1. Synthesis

Tantalum and niobium perovskites are extensively investigated for their dielectric properties or their photocatalytic activity in water splitting among other chemical reactions. Alkaline earth oxynitride perovskites were initially prepared by solid state reaction between the carbonates of calcium, strontium, or barium and Nb2O5 or Ta2O5 at 950–1000 °C under gaseous ammonia.15 Alternative synthetic approaches have used precursor oxides such as Ca2Nb2O7,3 Sr2Nb2O7, or SrNbO3 for treatment at similar temperatures under NH354 or other nitriding agents such as urea.55 Synthesis under N2 gas requires higher temperatures, up to 1500 °C, producing highly crystalline materials and sintered ceramics suitable for electrical measurements. TaON, Ta3N5, or TaN have been used as reagents, mixed with the alkaline earth carbonate or oxide, for the synthesis of CaTaO2N, SrTaO2N, and BaTaO2N.17,56,57 More recently SrNbO2N has been prepared in similar conditions, starting with a mixture of NbN and SrCO3.58 Large crystals, with sizes up to 10 µm, have been obtained for Sr and Ba perovskites by ammonothermal synthesis at 627 °C, starting from Nb or Ta and Sr or Ba metals and using NaN3 and NaOH as mineralizers.59 For BaNbO2N, a self propagating high temperature synthesis method has been recently used, starting with Ba(OH)2, NbCl5, and NaNH2. The reaction took place heating at 225 °C,60 and the thermodynamical driving force was the formation of NaCl together with BaNbO2N. A similar reaction was previously reported for BaTaO2N at 223 °C although it was not described as explosive.61 These are the lowest temperatures reported up to now for the synthesis of perovskite oxynitrides.

Rare earth perovskite oxynitrides LnBON2 with Ln = La, Ce, Pr, Nd, Sm and Gd or EuBO2N (B = Nb, Ta) are generally prepared by treating the scheelites LnBO4 under NH3 at 950 °C.6,12,25 Ammonothermal synthesis has also been used, by reacting the metals or their alloys with NaN3 or NaNH2 and NaOH at pressures of 100–300 MPa.62–65 This method produces crystals with sizes up to 15 µm.

2. Crystal symmetries and anion order

Some tantalum and niobium oxynitride perovskites look cubic from laboratory x-ray diffraction data, but they show distortions from synchrotron x-ray diffraction, electron diffraction, or neutron diffraction data. BaTaO2N and BaNbO2N have only been reported in the ideal cubic structure Pm-3m.66 Neutron diffraction data of SrTaO2N and SrNbO2N are refined using the space group I4/mcm in the superstructure 2 ap × 2 ap × 2 ap due to ordered rotations of the octahedra,17,67,68 and electron diffraction showed symmetry lowering to Fmmm induced by anion order11,29 (Fig. 1). The observed anion distribution in both compounds is consistent with a cis configuration of nitrides stabilized by covalency and the formation of disordered zig-zag N-M-N chains as suggested for other perovskite oxynitrides including cubic BaTaO2N.69–71 In the Ba1−xSrxTaO2N series, a sharp crossover from two-dimensional to three-dimensional distribution of cis-TaN chains occurs for x near 0.2 (Fig. 4).71 

FIG. 4.

Plot of oxygen occupancies from room temperature neutron refinements against x in the Ba1−xSrxTaO2N series for the c-axis anion site. Values for the x = 0–0.2 cubic Pm3¯m refinements are fixed at 0.67 which averages over the 3D cis-TaN chains. Occupancies for the x = 0.4–1 samples are refined against the tetragonal P4/mmm model which averages the 2D cis-TaN chains model. Reproduced with permission from Johnston et al., Chem. Commun. 54, 5245 (2018). Copyright 2018 Royal Society of Chemistry.

FIG. 4.

Plot of oxygen occupancies from room temperature neutron refinements against x in the Ba1−xSrxTaO2N series for the c-axis anion site. Values for the x = 0–0.2 cubic Pm3¯m refinements are fixed at 0.67 which averages over the 3D cis-TaN chains. Occupancies for the x = 0.4–1 samples are refined against the tetragonal P4/mmm model which averages the 2D cis-TaN chains model. Reproduced with permission from Johnston et al., Chem. Commun. 54, 5245 (2018). Copyright 2018 Royal Society of Chemistry.

Close modal

CaTaO2N with the GdFeO3 type structure shows N/O distribution similar to SrTaO2N and SrNbO2N compounds.67 Divalent europium compounds EuTaO2N and EuNbO2N show structural distortions similar to SrTaO2N and SrNbO2N,6 in contrast to the remaining rare earth compounds that show more distorted structures, with different tilting systems and space groups I2/m or Immma for LaTaON212,29,67 and Pnma for LaNbON2,72 CeTaON2, and PrTaON2.12 The anion distributions reported for LaTaON2 and LaNbON2 are similar to those found in SrTaO2N, SrNbO2N, LaTiO2N and in vanadium oxynitride perovskites, consistent with a cis configuration of nitrides (Fig. 1). Recent DFT studies have shown that anion order has an important effect on the bandgaps and band edge positions of CaTaO2N and SrTaO2N, affecting the photocatalytic activity and other properties.14,73 Epitaxial strain in thin films of Ca1−xSrxTaO2N has been found to affect the anion order in a recent study performed by a linearly polarized x-ray absorption near-edge structure (XANES) and electron microscopy.74 

Ruddlesden–Popper75,76 perovskite oxynitrides (AX)(ABX3)n (X = N, O) have been reported for tantalum and niobium. n = 1 Sr2TaO3N77 and Sr2NbO3N, and n = 2 Sr3Nb2O5N221 crystallize in space group I4/mmm. For A = rare earth, the only reported examples are n = 2 Eu3Ta2N4O3, which has been recently prepared by ammonothermal synthesis,78 and the related compound Li2LaTa2O6N, that shows lithium with tetrahedral co-ordination in the AX layers.79 For n = 1 compounds, neutron diffraction studies show that anions order partially so nitrogen and oxygen occupy the 4c equatorial sites with 50% occupancies, and oxygen prefers the 4e axial positions.80,81 This order can be rationalized by Pauling’s second crystal rule10,82 because the equatorial sites show larger bond strength sums than the axial ones, and it is also consistent with the local cis order of nitrides suggested for pseudocubic perovskites.

3. Photocatalytic properties

Extensive investigation on the photocatalytic activity of tantalum and niobium perovskite oxynitrides in water oxidation and reduction has been developed by Domen’s group.2,34,83 The alkaline earth compounds of Ca, Sr, and Ba show bandgaps between 1.7 eV (BaNbO2N) and 2.4 eV (CaTaO2N), with corresponding absorption edges between 730 nm and 510 nm, respectively.84–86 Some of these perovskites have adequate potentials for photocatalytic water oxidation and reduction;87,88 however, except for CaTaO2N,89 they cannot achieve the overall water splitting. Recent progress has been made in lanthanum based compounds. The complex oxynitride LaMg1/3Ta2/3O2N, with a cation disordered double perovskite structure, was first reported by Kim and Woodward.90 It has been reported as the first example of a overall water splitting photocatalyst active under visible light up to 600 nm91,92 and the most promising material with respect to its wide range of usable wavelengths. LaTaON2 shows a bandgap of 1.9 eV (absorption edge of 640 nm) and can evolve H2 and O2 from aqueous solution.93 The H2 evolution activity is weak, but it can be enhanced in core-shell structures obtained by ammonolysis of LaKNaTaO5.94 

4. Electronic properties

The dielectric properties of tantalum perovskites SrTaO2N and BaTaO2N were initially investigated by Marchand et al.95 and further by Kim et al. that reported relative permittivities at room temperatures of 4900 and 2900, respectively.3 Further measurements performed on dense ceramics led lower values of 450 for SrTaO2N96 and 320–620 for BaTaO2N.97 Ferroelectricity in SrTaO2N has been reported for epitaxial thin films98 and in the surface of sintered ceramics post-annealed in NH3.8 Both compounds are centrosymmetric, and the origin of their high dielectric constants or ferroelectricity is under discussion although it is generally ascribed to the presence of local electrical dipoles induced by the anion order in the TaO4N2 octahedra.69,99

Analogous divalent europium compounds EuTaO2N and EuNbO2N are electrically insulating and show ferromagnetism induced by coupling of europium 7/2 spins.6 The niobium compound may show slight nitrogen deficiency which induces giant magnetoresistance as a consequence of coupling between the Eu2+ spins and the Nb4+ carriers.

Perovskite oxynitrides of group 6 have been less investigated than for other early transition metals. All of them show nitrogen non-stoichiometry and form solid solutions ABO3−xNx where the transition metal shows mixed valence states of +3/+4 for Cr, +4/+5 or +5/+6 for Mo, and +5/+6 for W. Chromium compounds have only been reported for LnCrO3−xNx with Ln = La, Pr, and Nd and nitrogen contents up to x = 0.59, that have been investigated for their magnetic properties.100 They are prepared by nitriding LnCrO4 precursors under NH3 for long treatment times and high flow rates. The ammonolysis reaction proceeds similarly to that observed for LnVO3−xNx perovskites, with a first reduction step of LnCrO4 to poorly nitride LnCrO3−xNx compounds with chromium mainly in +3 state, followed by increased incorporation of nitride with concomitant oxidation of Cr3+ to Cr4+. LnCrO3 perovskites crystallize in the GdFeO3 type structure and show antiferromagnetic order of Cr3+ spins which varies with the size and 4fn moments of the Ln3+ cations.101 The hole doping trough O2−/N3− anion substitution decreases the Néel temperature but less drastically than for cation substitutions of Ln3+ by rare earth cations. The larger covalency of metal-nitride bonds compared to metal-oxide bonds increases the antiferromagnetic interaction between Cr atoms, compensating for the reduction of TC induced by hole doping (Fig. 5).

FIG. 5.

Cr spin ordering temperatures corrected for lattice effects for doped LnCrO3 materials [LnCrO3−xNx (Ln = La, Pr, Nd), La1−xSrxCrO3, and La1−xCaxCrO3] as a function of Cr4+. Reproduced with permission from Black et al., Chem. Commun. 52, 4317 (2016). Copyright 2016 Royal Society of Chemistry.

FIG. 5.

Cr spin ordering temperatures corrected for lattice effects for doped LnCrO3 materials [LnCrO3−xNx (Ln = La, Pr, Nd), La1−xSrxCrO3, and La1−xCaxCrO3] as a function of Cr4+. Reproduced with permission from Black et al., Chem. Commun. 52, 4317 (2016). Copyright 2016 Royal Society of Chemistry.

Close modal

Molybdenum and tungsten perovskite oxynitrides have been explored for their magnetic and thermoelectric properties and more recently as photocatalysts in several chemical reactions. Molybdenum compounds have only been reported for strontium in the A sites. The treatment in NH3 at 750–900 °C of SrMoO4 scheelites produces cubic Pm-3m SrMoO3−xNx (0.40 ≤ x ≤ 1.27)5,20,102,103 perovskites that have been investigated as thermoelectric materials. Tungsten compounds were first reported by Marchand et al., that prepared tetragonal LnWO3−xNx perovskites (Ln = La, Nd; x = 2.2, 2.3, 2.4)104 by treatment of Ln2W2O9 in ammonia at temperatures between 700 °C and 900 °C. These compounds have been recently prepared as thin films105 by radiofrequency reactive sputtering, using elemental La and W targets and Si substrates. SrWO2N106 can be prepared in similar conditions to SrMoO3−xNx. It shows high stability as photocatalyst in oxygen evolution under visible light, in contrast to the lanthanide perovskites LnWO3−xNx (Ln = La, Pr, Nd, Eu) that evolve N2.107 Highly porous LaWO3−xNx has been recently reported as a photoelectrocatalyst for water splitting under infrared light, at wavelengths above 780 nm.108 Pseudocubic EuWO1+xN2−x compounds are prepared by ammonolysis of Eu2W2O9 with N contents tuned by the ammonia flow rate and temperature.46 They may show europium in +2/+3 oxidation states and tungsten in +5/+6 oxidation states, which leads to different electrical and magnetic properties as a function of the N/O ratio. They order ferromagnetically at 12 K, and colossal magnetoresistances at low temperatures are observed for the least doped sample (x = −0.04).

Double perovskite oxynitrides of tungsten or molybdenum and iron are prepared by topochemical nitridation of the corresponding cation ordered oxides. The ammonolysis of Sr2FeWO6 at temperatures between 600 °C and 660 °C produces new antiferromagnetic Sr2FeWO6−xNx compounds that keep the cation order of the precursor oxide, with 0 < x ≤ 1, and Néel temperatures between 37 K and 13 K.109 A similar synthetic route has been used to investigate the effect of nitride on Sr2FeMoO6, an important material that shows metallic conductivity, ferromagnetism, and magnetoresistance at room temperature. The topochemical nitridation of this oxide leads the cation ordered double perovskite oxynitride Sr2FeMoO4.9N1.1 that is ferromagnetic with Tc ≈ 100 K and also shows negative magnetoresistance.110 The two oxynitrides Sr2FeWO5N and Sr2FeMoO4.9N1.1 show superstructures of the perovskite subcell with parameters 2 ap × 2 ap × 2 ap and 2 ap × 2 ap × 2 ap, respectively. The tolerance factor increases with nitriding as a consequence of the oxidation of the B cations (Fe2+ to Fe3+and Fe4+, and Mo5+ to Mo6+), inducing symmetry increasing, from P21/n for Sr2FeWO6 to I4/m for Sr2FeWO5N and from I4/m for Sr2FeMoO6 to Fm-3m for Sr2FeMoO4.9N1.1. The introduction of nitride in Sr2FeMoO6 produces changes in the magnetic structure related to the lowering of the Fermi level associated with the oxidation of iron and to carrier localization induced by anion disorder (Fig. 6).

FIG. 6.

[(a) and (b)] Schematic band filing of Sr2FeMoO6 and [(c) and (d)] Sr2FeMoO4.9N1.1. In (d), localized states are formed around defect-related potential wells (e.g., nitride sites, Jahn-Teller Fe4+ ions) that trap electrons, hindering carrier mobility, weakening double exchange ferromagnetic interactions, and canceling long range ordering. Reproduced with permission from Ceravola et al., Chem. Commun. 55, 3105 (2019). Copyright 2019 Royal Society of Chemistry.

FIG. 6.

[(a) and (b)] Schematic band filing of Sr2FeMoO6 and [(c) and (d)] Sr2FeMoO4.9N1.1. In (d), localized states are formed around defect-related potential wells (e.g., nitride sites, Jahn-Teller Fe4+ ions) that trap electrons, hindering carrier mobility, weakening double exchange ferromagnetic interactions, and canceling long range ordering. Reproduced with permission from Ceravola et al., Chem. Commun. 55, 3105 (2019). Copyright 2019 Royal Society of Chemistry.

Close modal

Research on transition metal perovskite oxynitrides has progressed substantially in the last years, triggered by important applications that promoted the search of new compounds and the development of synthetic methods. Intensive explorative work of new photocatalysts in water splitting has been performed, leading to the recent discovery of notable materials such as LaMg1/3Ta2/3O2N, a double perovskite oxynitride with low cation order that shows a wide range of usable wavelengths. New hybrid photocatalysts of perovskite oxynitrides active under visible light have been developed for other important chemical reactions such as CO2 reduction.111 In the field of electronic materials, ferroelectricity has recently been observed, induced by N/O order, and efforts to produce sintered ceramics have led to improved processing strategies.112 These include a high pressure/high temperature treatment performed under N2 to obtain dense ceramics, followed by a simple ammonolysis step for recovering the nitrogen loss that happens at high temperatures and is inherent to some oxynitrides. New strategies for producing dense single crystal thin films with control of anion order have been developed74 with direct evaluation of N/O distribution through STEM-EELS.

Reported layered perovskite oxynitrides are scarce; however, they show potential tunability of bandgaps and electronic states of the transition metals and are candidates for searching new materials. Oxidic double perovskites A2B′B″O6113 show a large diversity of properties as a result of the combination of two different transition metals. Double perovskite oxynitrides A2B′B″O6−xNx have been reported for few transition metals and represent another source of new materials. Late transition metals such as iron have been stabilized in perovskite oxynitrides by using adequate precursors for ammonolysis reactions at lower temperatures. Efforts in the development of synthetic strategies should lead to the discovery of important materials in these and other unexplored groups of compounds.

This work was supported by the Spanish Ministerio de Ciencia, Universidades e Investigación, Spain (Project No. MAT2017-86616-R), and from Generalitat de Catalunya (Grant No. 2017SGR581). ICMAB acknowledges financial support from MINECO through the Severo Ochoa Program (Grant No. SEV-2015-0496).

1.
A.
Fuertes
,
Dalton Trans.
39
,
5942
(
2010
).
2.
T.
Takata
and
K.
Domen
,
ACS Energy Lett.
4
,
542
(
2019
).
3.
Y.
Kim
,
P. M.
Woodward
,
K. Z.
Baba-Kishi
, and
C. W.
Tai
,
Chem. Mater.
16
,
1267
(
2004
).
4.
M.
Jansen
and
H. P.
Letschert
,
Nature
404
,
980
(
2000
).
5.
D.
Logvinovich
,
R.
Aguiar
,
R.
Robert
,
M.
Trottmann
,
S. G.
Ebbinghaus
,
A.
Reller
, and
A.
Weidenkaff
,
J. Solid State Chem.
180
,
2649
(
2007
).
6.
A. B.
Jorge
,
J.
Oró-Sole
,
A. M.
Bea
,
N.
Mufti
,
T. T. M.
Palstra
,
J. A.
Rodgers
,
J. P.
Attfield
, and
A.
Fuertes
,
J. Am. Chem. Soc.
130
,
12572
(
2008
).
7.
T.
Yajima
,
F.
Takeiri
,
K.
Aidzu
,
H.
Akamatsu
,
K.
Fujita
,
W.
Yoshimune
,
M.
Ohkura
,
S.
Lei
,
V.
Gopalan
,
K.
Tanaka
,
C. M.
Brown
,
M. A.
Green
,
T.
Yamamoto
,
Y.
Kobayashi
, and
H.
Kageyama
,
Nat. Chem.
7
,
1017
(
2015
).
8.
S.
Kikkawa
,
S.
Sun
,
Y.
Masubuchi
,
Y.
Nagamine
, and
T.
Shibahara
,
Chem. Matter
28
,
1312
(
2016
).
9.
R.
Asahi
,
T.
Morikawa
,
T.
Ohwaki
,
K.
Aoki
, and
Y.
Taga
,
Science
293
,
269
(
2001
).
10.
A.
Fuertes
,
Inorg. Chem.
45
,
9640
(
2006
).
11.
M.
Yang
,
J.
Oró-Solé
,
J. A.
Rodgers
,
A. B.
Jorge
,
A.
Fuertes
, and
J. P.
Attfield
,
Nat. Chem.
3
,
47
(
2011
).
12.
S. H.
Porter
,
Z.
Huang
, and
P. M.
Woodward
,
Cryst. Growth Des.
14
,
117
(
2014
).
13.
J. P.
Attfield
,
Cryst. Growth Des.
13
,
4623
(
2013
).
14.
A.
Ziani
,
C.
Le Paven
,
L.
Le Gendre
,
F.
Marlec
,
R.
Benzerga
,
F.
Tessier
,
F.
Cheviré
,
M. N.
Hedhili
,
A. T.
Garcia-Esparza
,
S.
Melissen
,
P.
Sautet
,
T.
Le Bahers
, and
K.
Takanabe
,
Chem. Matter
29
,
3989
(
2017
).
15.
R.
Marchand
,
F.
Pors
, and
Y.
Laurent
,
Rev. Int. Hautes Temp. Refract.
23
,
11
(
1986
).
16.
A.
Fuertes
,
Prog. Solid State Chem.
51
,
63
(
2018
).
17.
S. J.
Clarke
,
K. A.
Hardstone
,
C. W.
Michie
, and
M. J.
Rosseinsky
,
Chem. Mater.
14
,
2664
(
2002
).
18.
R.
Marchand
,
C. R. Acad. Sci. Paris
282
,
329
(
1976
).
19.
R.
Marchand
and
Y.
Laurent
, Patent CNRS-ANVAR 84-17274 (
13 November 1984
).
20.
G.
Liu
,
X.
Zhao
, and
H. A.
Eick
,
J. Alloys Compd.
187
,
145
(
1992
).
21.
G.
Tobías
,
J.
Oró-Solé
,
D.
Beltrán-Porter
, and
A.
Fuertes
,
Inorg. Chem.
40
,
6867
(
2001
).
22.
S. J.
Clarke
,
B. P.
Guinot
,
C. W.
Michie
,
M. J. C.
Calmont
, and
M. J.
Rosseinsky
,
Chem. Mater.
14
,
288
(
2002
).
23.
S. G.
Ebbinghaus
,
H.-P.
Abicht
,
R.
Dronskowski
,
T.
Müller
,
A.
Reller
, and
A.
Weidenkaff
,
Prog. Solid State Chem.
37
,
173
(
2009
).
24.
A.
Fuertes
,
J. Mater. Chem.
22
,
3293
(
2012
).
25.
R.
Marchand
,
F.
Pors
, and
Y.
Laurent
,
Ann. Chim.
16
,
553
(
1991
).
26.
R.
Okada
,
K.
Katagiri
,
Y.
Masubuchi
, and
K.
Inumaru
,
Eur. J. Inorg. Chem.
2019
,
1257
.
27.
M.
Yashima
,
M.
Saito
,
H.
Nakano
,
T.
Takata
,
K.
Ogisu
, and
K.
Domen
,
Chem. Commun.
46
,
4704
(
2010
).
28.
D.
Habu
,
Y.
Masubuchi
,
S.
Torii
,
T.
Kamiyama
, and
S.
Kikkawa
,
J. Solid State Chem.
237
,
254
(
2016
).
29.
L.
Clark
,
J.
Oró-Solé
,
K. S.
Knight
,
A.
Fuertes
, and
J. P.
Attfield
,
Chem. Mater.
25
,
5004
(
2013
).
30.
J.
Oró-Solé
,
L.
Clark
,
W.
Bonin
,
J. P.
Attfield
, and
A.
Fuertes
,
Chem. Commun.
49
,
2430
(
2013
).
31.
S.
Ninova
and
U.
Aschauer
,
J. Mater. Chem. A
7
,
2129
(
2019
).
32.
A.
Kasahara
,
K.
Nukumizu
,
G.
Hitoki
,
T.
Takata
,
J. N.
Kondo
,
M.
Hara
,
H.
Kobayashi
, and
K.
Domen
,
J. Phys. Chem. A
106
,
6750
(
2002
).
33.
C.
Le Paven-Thivet
,
A.
Ishikawa
,
A.
Ziani
,
L.
Le Gendre
,
M.
Yoshida
,
J.
Kubota
,
F.
Tessier
, and
K.
Domen
,
J. Phys. Chem. C
113
,
6156
(
2009
).
34.
C. M.
Leroy
,
A. E.
Maegli
,
K.
Sivula
,
T.
Hisatomi
,
N.
Xanthopoulos
,
E. H.
Otal
,
S.
Yoon
,
A.
Weidenkaff
,
R.
Sanjines
, and
M.
Grätzel
,
Chem. Commun.
48
,
820
(
2012
).
35.
F.
Zhang
,
A.
Yamakata
,
K.
Maeda
,
Y.
Moriya
,
T.
Takata
,
J.
Kubota
,
K.
Teshima
,
S.
Oishi
, and
K.
Domen
,
J. Am. Chem. Soc.
134
,
8348
(
2012
).
36.
T.
Hisatomi
and
K.
Domen
,
Nat. Catal.
2
,
387
(
2019
).
37.
M.
Hojamberdiev
,
A.
Yamaguchi
,
K.
Yubuta
,
S.
Oishi
, and
K.
Teshima
,
Inorg. Chem.
54
,
3237
(
2015
).
38.
L.
Lu
,
B.
Wang
,
S.
Wang
,
Z.
Shi
,
S.
Yan
, and
Z.
Zou
,
Adv. Funct. Mater.
27
,
1702447
(
2017
).
39.
D.
Fasquelle
,
A.
Ziani
,
C.
Le Paven-Thivet
,
L.
Le Gendre
, and
J. C.
Carru
,
Matter Lett.
65
,
3102
(
2011
).
40.
Y.
Lu
,
C.
Le Paven
,
H. V.
Nguyen
,
R.
Benzerga
,
L.
Le Gendre
,
S.
Rioual
,
F.
Tessier
,
F.
Cheviré
,
A.
Sharaiha
,
C.
Delaveaud
, and
X.
Castel
,
Cryst. Growth Des.
13
,
4852
(
2013
).
41.
D.
Chen
,
D.
Habu
,
Y.
Masubuchi
,
S.
Torii
, and
T.
Kamiyama
,
Solid State Sci.
54
,
2
(
2016
).
42.
N.
Vonrüti
and
U.
Aschauer
,
Phys. Rev. Lett.
120
,
046001
(
2018
).
43.
S. H.
Porter
,
Z.
Huang
,
Z.
Heng
,
M.
Avdeev
,
Z.
Chen
,
S.
Dou
, and
P. M.
Woodward
,
J. Solid State Chem.
226
,
279
(
2015
).
44.
S. H.
Porter
,
Z.
Huang
,
S.
Dou
,
S.
Brown-Xu
,
A. T. M. G.
Sarwar
,
R. C.
Myers
, and
P. M.
Woodward
,
Chem. Matter
27
,
2414
(
2015
).
45.
R.
Mikita
,
T.
Aharen
,
T.
Yamamoto
,
F.
Takeiri
,
T.
Ya
,
W.
Yoshimune
,
K.
Fujita
,
S.
Yoshida
,
K.
Tanaka
,
D.
Batuk
,
A. M.
Abakumov
,
C. M.
Brown
,
Y.
Kobayashi
, and
H.
Kageyama
,
J. Am. Chem. Soc.
138
,
3211
(
2016
).
46.
M.
Yang
,
J.
Oró-Solé
,
A.
Kusmartseva
,
A.
Fuertes
, and
J. P.
Attfield
,
J. Am. Chem. Soc.
132
,
4822
(
2010
).
47.
A. P.
Black
,
H.
Suzuki
,
M.
Higashi
,
C.
Frontera
,
C.
Ritter
,
C.
De
,
A.
Sundaresan
,
R.
Abe
, and
A.
Fuertes
,
Chem. Commun.
54
,
1525
(
2018
).
48.
M.
Yang
,
J. A.
Rodgers
,
L. C.
Middler
,
J.
Oró-Solé
,
A. B.
Jorge
,
A.
Fuertes
, and
J. P.
Attfield
,
Inorg. Chem.
48
,
11498
(
2009
).
49.
A. P.
Black
, Ph.D. thesis,
Autonomous University of Barcelona
,
2017
.
50.
A.
Feteira
,
D. C.
Sinclair
,
K. Z.
Rajab
, and
M. T.
Lanagan
,
J. Am. Ceram. Soc.
91
,
893
(
2008
).
51.
P.
Antoine
,
R.
Assaba
,
P.
L’Haridon
,
R.
Marchand
,
Y.
Laurent
,
C.
Michel
, and
B.
Raveau
,
Mater. Sci. Eng.: B
5
,
43
(
1989
).
52.
J.
Oró-Solé
,
L.
Clark
,
N.
Kumar
,
W.
Bonin
,
A.
Sundaresan
,
J. P.
Attfield
,
C. N.
Rao
, and
A.
Fuertes
,
J. Mater. Chem. C
2
,
2212
(
2014
).
53.
M.
Sano
,
Y.
Hirose
,
S.
Nakao
, and
T.
Hasegawa
,
J. Mater. Chem. C
5
,
1798
(
2017
).
54.
M.
Kodera
,
Y.
Moriya
,
M.
Katayama
,
T.
Hisatomi
,
T.
Minegishi
, and
K.
Domen
,
Sci. Rep.
8
,
15849
(
2018
).
55.
A.
Gomathi
,
S.
Reshma
, and
C. N. R.
Rao
,
J. Solid State Chem.
182
,
72
(
2009
).
56.
S.-K.
Sun
,
T.
Motohashi
,
Y.
Masubuchi
, and
S.
Kikkawa
,
J. Eur. Ceram. Soc.
34
,
4451
(
2014
).
57.
S.-K.
Sun
,
Y.
Masubuchi
,
T.
Motohashi
, and
S.
Kikkawa
,
J. Eur. Ceram. Soc.
35
,
3289
(
2015
).
58.
W.-B.
Niu
,
S.-K.
Sun
,
W.-M.
Guo
,
S.-L.
Chen
,
M.
Lv
,
H.-T.
Lin
, and
C.-Y.
Wang
,
Ceram. Int.
44
,
23324
(
2018
).
59.
N.
Cordes
,
T.
Bräuniger
, and
W.
Schnick
,
Eur. J. Inorg. Chem.
2018
,
5019
.
60.
J.
Odahara
,
A.
Miura
,
N. C.
Rosero-Navarro
, and
K.
Tadanaga
,
Inorg. Chem.
57
,
24
(
2018
).
61.
Y.
Setsuda
,
Y.
Maruyama
,
C.
Izawa
, and
T.
Watanabe
,
Chem. Lett.
46
,
987
(
2017
).
62.
T.
Watanabe
,
K.
Tajima
,
J. W.
Li
,
N.
Matsushita
, and
M.
Yoshimura
,
Chem. Lett.
40
,
1101
(
2011
).
63.
C.
Izawa
,
T.
Kobayashi
,
K.
Kishida
, and
T.
Watanabe
,
Adv. Mat. Sci. Eng.
2014
,
465720
.
64.
N.
Cordes
and
W.
Schnick
,
Chem. - Eur. J.
23
,
11410
(
2017
).
65.
J.
Häusler
and
W.
Schnick
,
Chem. - Eur. J.
24
,
11864
(
2018
).
66.
F.
Pors
,
R.
Marchand
, and
Y.
Laurent
,
Mater. Res. Bull.
23
,
1447
(
1988
).
67.
E.
Gunther
,
R.
Hagenmayer
, and
M.
Jansen
,
Z. Anorg. Allg. Chem.
626
,
1519
(
2000
).
68.
S. G.
Ebbinghaus
,
A.
Weidenkaff
,
A.
Rachel
, and
A.
Reller
,
Acta Crystallogr., Sect. C: Cryst. Struct. Commun.
60
,
i91
(
2004
).
69.
K.
Page
,
M. W.
Stoltzfus
,
Y.-I.
Kim
,
T.
Proffen
,
P. M.
Woodward
,
A. K.
Cheetham
, and
R.
Seshadri
,
Chem. Mater.
19
,
4037
(
2007
).
70.
H.
Wolff
and
R.
Dronskowski
,
J. Comput. Chem.
29
,
2260
(
2008
).
71.
H.
Johnston
,
A. P.
Black
,
P.
Kayser
,
J.
Oró-Solé
,
D. A.
Keen
,
A.
Fuertes
, and
J. P.
Attfield
,
Chem. Commun.
54
,
5245
(
2018
).
72.
D.
Logvinovich
,
S. G.
Ebbinghauss
,
A.
Reller
,
I.
Marozau
,
D.
Ferri
, and
A.
Weidenkaff
,
Z. Anorg. Allg. Chem.
636
,
905
(
2010
).
73.
A.
Kubo
,
G.
Giorgi
, and
K.
Yamashita
,
Chem. Mater.
29
,
539
(
2017
).
74.
D.
Oka
,
Y.
Hirose
,
F.
Matsui
,
H.
Kamisaka
,
T.
Oguchi
,
N.
Maejima
,
H.
Nishikawa
,
T.
Muro
,
K.
Hayashi
, and
T.
Hasegawa
,
ACS Nano
11
,
3860
(
2017
).
75.
S. N.
Ruddlesden
and
P.
Popper
,
Acta Crystallogr.
10
,
538
(
1957
).
76.
S. N.
Ruddlesden
and
P.
Popper
,
Acta Crystallogr.
11
,
54
(
1958
).
77.
F.
Pors
,
R.
Marchand
, and
Y.
Laurent
,
Ann. Chim.
16
,
547
(
1991
).
78.
N.
Cordes
,
M.
Nentwig
,
L.
Eisenburger
,
O.
Oeckler
, and
W.
Schnick
,
Eur. J. Inorg. Chem.
2019
,
2304
.
79.
M.
Kaga
,
H.
Kurachi
,
T.
Asaka
,
B.
Yue
,
J.
Ye
, and
K.
Fukuda
,
Powder Diffr.
26
,
4
(
2011
).
80.
N.
Diot
,
R.
Marchand
,
J.
Haines
,
J. M.
Léger
,
P.
Macaudière
, and
S.
Hull
,
J. Solid State Chem.
146
,
390
(
1999
).
81.
G.
Tobías
,
D.
Beltrán-Porter
,
O.
Lebedev
,
G.
Van Tendeloo
,
J.
Oró-Solé
,
J.
Rodríguez-Carvajal
, and
A.
Fuertes
,
Inorg. Chem.
43
,
8010
(
2004
).
82.
L.
Pauling
,
J. Am. Chem. Soc.
51
,
1010
(
1929
).
83.
T.
Takata
,
C.
Pan
, and
K.
Domen
,
ChemElectroChem
3
,
31
(
2016
).
84.
I. E.
Castelli
,
T.
Olsen
,
S.
Datta
,
D. D.
Landis
,
S.
Dahl
,
K. S.
Thyegesen
, and
K. W.
Jacobsen
,
Energy Environ. Sci.
5
,
5814
(
2012
).
85.
Y.
Wu
,
P.
Lazic
,
G.
Hautier
,
K.
Persson
, and
G.
Ceder
,
Energy Environ. Sci.
6
,
157
(
2013
).
86.
S.
Balaz
,
S. H.
Porter
,
P. M.
Woodward
, and
L. J.
Brillson
,
Chem. Mater.
25
,
3337
(
2013
).
87.
K.
Maeda
,
D.
Lu
, and
K.
Domen
,
Angew. Chem., Int. Ed.
52
,
6488
(
2013
).
88.
J.
Seo
,
T.
Hisatomi
,
M.
Nakabayashi
,
N.
Shibata
,
T.
Minegishi
,
M.
Katayama
, and
K.
Domen
,
Adv. Energy Mater.
8
,
1800094
(
2018
).
89.
J.
Xu
,
C.
Pan
,
T.
Takata
, and
K.
Domen
,
Chem. Commun.
51
,
7191
(
2015
).
90.
Y.-I.
Kim
and
P. M.
Woodward
,
J. Solid State Chem.
180
,
3224
(
2007
).
91.
C.
Pan
,
T.
Takata
,
M.
Nakabayashi
,
T.
Matsumoto
,
N.
Shibata
,
Y.
Ikuhara
, and
K.
Domen
,
Angew. Chem., Int. Ed.
54
,
2955
(
2015
).
92.
C.
Pan
,
T.
Takata
, and
K.
Domen
,
Chem. - Eur. J.
22
,
1854
(
2016
).
93.
L.
Zhang
,
Y.
Song
,
J.
Feng
,
T.
Fang
,
Y.
Zhong
,
Z.
Li
, and
Z.
Zou
,
Int. J. Hydrogen Energy
39
,
7697
(
2014
).
94.
X.
Wang
,
T.
Hisatomi
,
Z.
Wang
,
J.
Song
,
J.
Qu
,
T.
Takata
, and
K.
Domen
,
Angew. Chem., Int. Ed.
58
,
10666
(
2019
).
95.
R.
Marchand
,
F.
Pors
,
Y.
Laurent
,
O.
Regreny
,
J.
Lostec
, and
J. M.
Haussone
,
J. Phys.
47
(
C1
),
901
(
1986
).
96.
S.-K.
Sun
,
Y.-R.
Zhang
,
Y.
Masubuchi
,
T.
Motohashi
, and
S.
Kikkawa
,
J. Am. Ceram. Soc.
97
,
1023
(
2014
).
97.
A.
Hosono
,
S.-K.
Sun
,
Y.
Masubuchi
, and
S.
Kikkawa
,
J. Eur. Ceram. Soc.
36
,
3341
(
2016
).
98.
D.
Oka
,
Y.
Hirose
,
H.
Kamisaka
,
T.
Fukumura
,
K.
Sasa
,
S.
Ishii
,
H.
Matsuzaki
,
Y.
Sato
,
Y.
Ikuhara
, and
T.
Hasegawa
,
Sci. Rep.
4
,
4987
(
2014
).
99.
R. L.
Withers
,
Y.
Liu
,
P.
Woodward
, and
Y.-I.
Kim
,
Appl. Phys. Lett.
92
,
102907
(
2008
).
100.
A. P.
Black
,
H. E.
Johnston
,
J.
Oró-Solé
,
B.
Bozzo
,
C.
Ritter
,
C.
Frontera
,
J. P.
Attfield
, and
A.
Fuertes
,
Chem. Commun.
52
,
4317
(
2016
).
101.
R. M.
Hornreich
,
J. Magn. Magn. Mater.
7
,
280
(
1978
).
102.
D.
Logvinovich
,
J.
Hejtmánek
,
K.
Knižek
,
M.
Maryško
,
N.
Homazava
,
P.
Toměs
,
R.
Aguiar
,
S. G.
Ebbinghaus
,
A.
Reller
, and
A.
Weidenkaff
,
J. Appl. Phys.
105
,
023522
(
2009
).
103.
W.
Li
,
D.
Li
,
X.
Gao
,
A.
Gurlo
,
S.
Zander
,
P.
Jones
,
A.
Navrotsky
,
Z.
Shen
,
R.
Riedel
, and
E.
Ionescu
,
Dalton Trans.
44
,
8238
(
2015
).
104.
P.
Antoine
,
R.
Marchand
,
Y.
Laurent
,
C.
Michel
, and
B.
Raveau
,
Mater. Res. Bull.
23
,
953
(
1988
).
105.
K. R.
Talley
,
J.
Magnum
,
C. L.
Perkins
,
R.
Woods-Robinson
,
A.
Mehta
,
B. P.
Gormn
,
G. L.
Brennecka
, and
A.
Zakutayev
,
Adv. Electron. Mater.
5
,
1900214
(
2019
).
106.
I. D.
Fawcett
,
K. V.
Ramanujachary
, and
M.
Greenblatt
,
Mater. Res. Bull.
32
,
1565
(
1997
).
107.
K.
Kawashima
,
M.
Hojamberdiev
,
H.
Wagata
,
E.
Zahedi
,
K.
Yubuta
,
K.
Domen
, and
K.
Teshima
,
J. Catal.
344
,
29
(
2016
).
108.
K.
Kawasima
,
Y.
Liu
,
J.-H.
Kim
,
B. R.
Wygat
,
I.
Cheng
,
H.
Celio
,
O.
Mabayoje
,
J.
Lin
, and
C. B.
Mullins
,
ACS Appl. Energy Mater.
2
,
913
(
2019
).
109.
R.
Ceravola
,
J.
Oró-Solé
,
A. P.
Black
,
C.
Ritter
,
I.
Puente Orench
,
I.
Mata
,
E.
Molins
,
C.
Frontera
, and
A.
Fuertes
,
Dalton Trans.
46
,
5128
(
2017
).
110.
R.
Ceravola
,
C.
Frontera
,
J.
Oró-Solé
,
A. P.
Black
,
C.
Ritter
,
I.
Mata
,
E.
Molins
,
J.
Fontcuberta
, and
A.
Fuertes
,
Chem. Commun.
55
,
3105
(
2019
).
111.
K.
Maeda
,
Prog. Solid State Chem.
51
,
52
(
2018
).
112.
Y.
Masubuchi
,
S.-K.
Sun
, and
S.
Kikkawa
,
Dalton Trans.
44
,
10570
(
2015
).
113.
S.
Vasala
and
M.
Karppinen
,
Prog. Solid State Chem.
43
,
1
(
2015
).