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Pauling's second crystal rule is used to predict the distribution of anions in mixed oxyanion systems such as oxynitrides and oxyhalides with diverse compositions and structure types. The results are presented in a plot correlating the charge of the anions obtained from the observed occupancies in crystallographic positions with the calculated bond strength sums for these sites.

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]

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]

A new solvent free protocol is presented to introduce amide and amine functionalities (N-aliphatic groups) onto graphene oxide in an energy efficient manner. Nitrogen contents of 3.6 wt% are obtained in only 5 minutes at room temperature by using ammonia gas as the nitrogen source for the ammonolysis of graphene oxide. [ABSTRACT FROM AUTHOR]

Electronic flexibility and colossal magnetoresistance effects are discovered in the perovskite oxynitrides EuW[O.sub.1+x][N.sub.2-x] and ammonolysis of [Eu.sub.2][W.sub.2][O.sub.9] has produced scheelite-type intermediates EuW[O.sub.4-y][N.sub.y] with a small degree of nitride substitution. Both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio, EuW[O.sub.1+x][N.sub.2-x] phases order ferromagnetically at 12 K and colossal magnetoresistances (CMR) are seen in the least doped sample.

The perovskite oxynitrides EuM[O.sub.2]N (M = Nb, Ta) are prepared and their coupled colossal magneto-resistive and capacitive effects are studied. The results have shown an excellent potential for large magneto-responses in materials like EuNb[O.sub.2]N, which has combined the large [Eu.sup.2+] spin and the off-center instability of [Nb.sup.5+] enhanced by bonding to nitride.

Rietveld method was used to refine the crystal structure of the n = 1 member of the Ruddlesden-Popper family (SrO)(SrNbO2N)n. The refined stoichiometry obtained by neutron diffraction for the n = 1 compound is Sr2-NbO3.28N0.72, indicating that a mixed-valence state for niobium, intermediate between +4 and +5 that results from a nitrogen deficiency with respect to the nominal stoichiometry.

The topotactic nitridation of cation ordered, tetragonal Sr2FeMoO6 in NH3 at moderate temperatures leads to cubic, Fm3̅m double perovskite oxynitride Sr2FeMoO4.9N1.1 where double-exchange interactions determine ferromagnetic order with TC≈ 100 K. Substitution of oxide by nitride induces bond asymmetries and local electronically driven structural distortions, which combined with Fermi level lowering restricts charge itinerancy to confined regions and preclude spontaneous long-range magnetic order. Under a magnetic field, ferromagnetic correlations expand, favoring charge delocalization and a negative magnetoresistance is observed. [ABSTRACT FROM AUTHOR]

Abstract Mixed anion oxides are emerging materials showing a variety of physical and chemical properties. Among them oxynitrides are widely investigated because of notable photocatalytic, dielectric, luminescent and electronic properties. Nitrides show more positive free energies of formation than oxides because of the higher stability of N 2 molecule with respect to O 2 and the unfavourable electron affinity of nitrogen compared to oxygen. However the stability of oxynitrides is higher than for nitrides, and they easily form from oxides in presence of reactive gases as NH 3. In addition to ammonolysis several synthetic strategies have been developed in the last years leading to the stabilization of relevant materials with a variety of structures. In this review we will discuss recent progress in the synthesis of oxynitrides emphasizing the importance of kinetic factors and the influence of preparative parameters on the structure types and oxidation states of the cations, and the consequences on physical properties. [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]

Topochemical nitridation in ammonia at moderate temperatures of cation ordered Sr2FeWO6 produces new antiferromagnetic double perovskite oxynitrides Sr2FeWO6−xNx with 0 ＜ x≤ 1. Nitrogen introduction induces the oxidation of Fe2+ to Fe3+ and decreases TN from 38 K (x = 0) to 13 K for Sr2FeWO5N which represents the first example of a double perovskite oxynitride with both high cationic order and nitrogen content. This synthetic approach can be extended to other cation combinations expanding the possibility of new materials in the large group of double perovskites. [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]

The solid solution Sr2−xLaxSiO4−xNx (0 ≥x≥ 1), obtained by concomitant substitution of Sr2+ by La3+ and O2− by N3− in Sr2SiO4, has been prepared by solid state reaction at 1500 °C in N2/H2 of mixtures of SrO, La2O3, SiO2 and Si3N4. Synchrotron radiation X-ray diffraction studies show a transition from the monoclinic P21/n symmetry of β-Sr2SiO4 to orthorhombic Pmnbα′,β-K2SO4 type phase for x≥ 0.2. The α′ phase is stabilized as a consequence of the increase in bond valence of the cations induced by nitriding. The activation with Eu2+ and Ce3+ of Sr2−xLaxSiO4−xNx produces luminescent materials with broad emission bands centered up to 650 nm under excitation at 405 nm. The emission wavelengths are tuned by La/N contents in a wide range with emission colours changing from yellow (x = 0.2) to orange-red (x = 1) for Eu2+ phosphors and from blue-green (x = 0.2) to orange-yellow (x = 1) in Ce3+ samples. [ABSTRACT FROM AUTHOR]

A simple crossover from two-dimensional to three-dimensional correlated disorder of O and N atoms on a cubic lattice has been discovered within the Ba1−xSrxTaO2N series of perovskite oxynitrides. The crossover is driven by lattice expansion as x decreases, and provides a rapid increase in entropy due to a change from subextensive to extensive configurational entropy regimes. [ABSTRACT FROM AUTHOR]

The new compounds LaSrSiO3N and LaBaSiO3N activated with Eu2+ are orange-red light-emitting luminescent materials under excitation in the UV-blue range. They represent the first examples of stoichiometric alkaline earth oxynitridosilicates with a β-K2SO4 structure. The isostructural compound LaEuSiO3N is ferromagnetic with a Curie temperature of 3 K and also shows red luminescence (λmax = 705 nm) under excitation at 405 nm. [ABSTRACT FROM AUTHOR]

Nitrogen-doped reduced graphene oxide (Ndoped RGO) samples with a high level of doping, up to 13 wt.%, have been prepared by annealing graphene oxide under a flow of pure ammonia. The presence of nitrogen within the structure of RGO induces a remarkable increase in the thermal stability against oxidation by air. The thermal stability is closely related with the temperature of synthesis and the nitrogen content. The combustion reaction of nitrogen in different coordination environments (pyridinic, pyrrolic, and graphitic) is analyzed against a graphene fragment (undoped) from a thermodynamic point of view. In agreement with the experimental observations, the combustion of undoped graphene turns out to be more spontaneous than when nitrogen atoms are present. [ABSTRACT FROM AUTHOR]

The rare earth vanadium oxynitride perovskites RVO3−xNx (R = La, Pr, Nd; 0 ≤x≤ 1) have been prepared by treatment of RVO4 precursors in NH3. The ammonolysis reactions proceed through an initial reduction of RVO4 precursors to RVO3 perovskites that are progressively nitrided and reoxidised to RVO3−xNx materials with varying proportions of V4+/V3+. Variable temperature neutron diffraction studies show that NdVO2N and PrVO2.24N0.76 have orthorhombic Pbnm symmetry between 3.5 and 300 K, but LaVO2.11N0.89 undergoes a broad Pbnm to R3̅c structural transition over this temperature range. In LaVO3−xNx samples the proportion of the R3̅c phase at room temperature increases with the nitrogen content. The partial anion order indicative of planes of cis-VN2 chains found in NdVO2N is also present in PrVO2.24N0.76, and is thus robust to the disorder created by non-stoichiometry. Magnetic measurements reveal spin freezing transitions at low temperatures in LaVO2.09N0.91 and PrVO2.24N0.76, but NdVO2N is paramagnetic. [ABSTRACT FROM AUTHOR]

Unusual subextensive configurational entropies that vary with particle size and tend to zero per atom in macroscopic samples are predicted for AMO3-zNz oxynitrides with perovskite type crystal structures. These materials are crystallographically disordered on the atomic scale, but local anion order produces chains of M-N-M bonds that undergo a 90° turn at each M cation, giving rise to subextensive entropies in materials such as SrTaO2N, LaNbON2, and EuWO1.5N1.5. A general Pauling ice-rules formula is used to calculate the extensive molar entropies for other cases such as SrMoO2.5N0.5 and BaTaO2N. The subextensive oxynitrides are usefully classified as showing an "open order", related to the correlated order of displacements in ferroelectric perovskites such as BaTiO3. This raises the possibility that further open-ordered oxynitride or molecular structures may be accessible, and other states such as spins and charges may also show novel open orders. [ABSTRACT FROM AUTHOR]

Transition-metal oxynitrides with perovskite-type structures are an emerging class of materials with optical, photocatalytic, dielectric and magnetoresistive properties that may be sensitive to oxide-nitride order, but the anion-ordering principles were unclear. Here we report an investigation of the representative compounds SrMO2N (M = Nb, Ta) using neutron and electron diffraction. This revealed a robust 1O/2(O0.5N0.5) partial anion order (up to at least 750 °C in the apparently cubic high-temperature phases) that directs the rotations of MO4N2 octahedra in the room-temperature superstructure. The anion distribution is consistent with local cis-ordering of the two nitrides in each octahedron driven by covalency, which results in disordered zigzag M-N chains in planes within the perovskite lattice. Local structures for the full range of oxynitride perovskites are predicted and a future challenge is to tune properties by controlling the order and dimensionality of the anion chains and networks. [ABSTRACT FROM AUTHOR]

Knowledge of the kinetic and thermodynamic behaviour of aqueous solutions containing two divalent cations and trans-1,2-cyclohexanediaminetetraacetate has been used to design synthetic pathways to ordered bimetallic complexes [ABSTRACT FROM AUTHOR]

The correlated anion order in the oxynitride perovskite NdVO2N, where disordered zig-zag VN chains segregate into planes within a pseudo-cubic lattice, is similar to that in materials such as SrTaO2N containing d0 transition metal cations. However, NdVO2N has 3d1 V4+ cations and the 3d-electrons are itinerant, showing that the anion chain order in oxynitride perovskites is robust to electron-doping. [ABSTRACT FROM AUTHOR]

Background Methods Results Conclusions Psoriasis (Ps) and atopic dermatitis (AD) are chronic systemic immune‐mediated diseases that can coexist in an overlapping condition called psoriasis dermatitis (PD). PD patients have intermediate lesions with characteristics of both Ps and AD. PD is very rare in adults but much more frequent in children. Little is known, however, about the course of PD in the pediatric population. The aim of this study was to evaluate the percentage of PD cases in children that evolved to a definite form of Ps or AD and to identify any clinical or epidemiological variables that could predict the course of the disease.We performed a prospective multicenter cohort study of children diagnosed with PD between January 2018 and December 2020. We collected participants' clinical and epidemiological characteristics, and pediatric dermatologists determined the percentage of participants who developed Ps or AD.The study included 24 children with PD, with a median age of 7.0 years. After a median follow‐up period of 31 months, 83.3% of cases had evolved to a definite form of Ps or AD (44.4% to Ps and 38.9% to AD). Younger age and family history of Ps were associated with progression to AD. Participants who progressed to AD or Ps had a longer follow‐up than those with an unchanged PD diagnosis.Given sufficient time, a large percentage of PD cases in children will evolve into Ps or AD. Long‐term clinical follow‐up is necessary for a correct diagnosis. [ABSTRACT FROM AUTHOR]

Titanium, zirconium and hafnium nitride halides show layered structures based on double slabs with compositions [X–M–N–N–M–X] (X = Cl, Br or I; M = Ti, Zr or Hf) that are separated by van der Waals gaps. Intercalation of electron donor species between the double layers induces superconductivity with critical temperatures up to 25.5 K. This review discusses the synthesis and structural chemistry of the hosts and intercalation compounds in this group of materials, as well as the influence of the structural and chemical features of the intercalates on the superconducting properties. [ABSTRACT FROM AUTHOR]