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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]

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]

Pauling's second crystal rule is shown to be able to predict in a general and simple way the distribution of anions in mixed oxyanion systems such as oxynitrides and oxyhalides with diverse compositions and structure types. 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. [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]

The thermodynamic stability of a series of nitrogen - doped reduced graphene oxides prepared by ammonolysis of graphene oxide has been investigated by high temperature oxidation calorimetry. In terms of enthalpy and depending on the concentration of nitrogen, the nitrogen - doped reduced graphene oxides can be up to 73 kJ·mol−1 more stable than graphite plus nitrogen. There is a linear relationship between the nitrogen content and the formation enthalpy, which indicates a decrease in stability with increasing nitrogen content. [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]

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]

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]

This work compares various methods to prepare polymer/carbon nanotube (CNT) composites for thermoelectric applications, focusing on the different doping mechanisms. We first look at the general trends observed in the Seebeck coefficient and power factor for a large number of composites as a function of electrical conductivity. Then we discuss two methods of nitrogen doping the carbon nanotubes in these composites, namely either during synthesis, or afterwards by ammonolysis. Finally, we discuss doping of the carbon nanotubes through charge transfer from the polymer counterpart, including photo-induced switching of the majority carrier type. As a general remark, we note that processability is negatively influenced by some doping procedures. Best results were achieved for unfunctionalized single-walled carbon nanotubes with a high content of semiconducting CNT species. [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]

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]

Physical and chemical properties of graphene can be tailored by nitrogen doping. As a consequence of the continuous race to achieve the highest possible amount of doping there is a growing tendency to assume that all N species are incorporated within the graphene lattice (doping). Here we show that this is not always the case and employ several complementary techniques that allow a proper assessment of the type of nitrogen present. The nature of the nitrogen atoms has been tuned by ammonolysis of graphene oxide in the range of 100 °C–800 °C. This allows us to expand the capabilities of the synthetic approach to afford not only N-doping (at high temperature) but also to introduce amine and amide moieties at 100 °C; the latter presenting a much higher dispersability in aqueous media than graphene oxide. Interestingly, the sample with the highest amount of nitrogen (14.7 wt. %) cannot be referred to as N-doped graphene since it also contains N-bearing aliphatic moieties. [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]

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]

A remarkable electronic flexibility and colossal magnetoresistance effects have been discovered in the perovskite oxynitrides EuWO1+xN2-x. Ammonolysis of Eu2W2O9 yields scheelite-type intermediates EuWO4-yNy with a very small degree of nitride substitution (y = 0.04) and then EuWO1+xN2-x perovskites that show a wide range of compositions -0.16 ⩽ x ⩽ 0.46. The cubic lattice parameter varies linearly with x, but electron microscopy reveals a tetragonal superstructure. The previously unobserved x < 0 regime corresponds to oxidation of Eu (hole doping of the Eu:4f band), whereas x > 0 materials have chemical reduction of W (electron doping of the W:5d band). Hence, both the Eu and W oxidation states and the hole/electron doping are tuned by varying the O/N ratio. EuWO1+xN2-x phases order ferromagnetically at 12K, and colossal magnetoresistances (CMR) are observed in the least doped (x= -0.04) sample. Distinct mechanisms for the hole and electron magnetotransport regimes are identified. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of the chemical and electrochemical alkali metal intercalation reactions in β-HfNCl has been investigated through electrochemical potential spectroscopy (EPS), in-situ powder X-ray diffraction during electrochemical intercalation and room temperature chemical intercalation experiments. EPS experiments in lithium cells reveal the presence of a plateau, at 1.8V vs. Li+/Li0 accounting for ca. 0.14mol Li, that indicates the formation of a new intermediate phase, and then a gradual decrease of potential with composition that extends up to very high lithium contents (ca. 1.1 per formula), consistent with the formation of a solid solution. Sodium electrochemical intercalation experiments showed a relatively similar behaviour with a plateau at 1.4V vs. Na+/Na0, corresponding to ca. 1.7V vs. Li+/Li0. In-situ monitored powder X-ray diffraction electrochemical intercalation experiments showed that the electrolyte solvent (ethylene carbonate/dimethyl carbonate, EC/DMC or propylene carbonate, PC) co-intercalated with the alkaline atom. This leads to a large expansion of the interlayer spacing that reaches a value of 21.06Å in the lithium co-intercalated phase with EC/DMC, Li x (EC/DMC) y HfNCl, and 22.01Å in the sodium co-intercalated phase with PC, Na x (PC) y HfNCl. Chemical intercalation using naphthyl-sodium solutions in tetrahydrofuran (THF) leads to solvent-free, multiple-phase samples showing in different proportions the pristine and the superconducting stage 2 and stage 1 phases. The composition of the intercalated samples depends on the pristine sample, the concentration of the naphthyl-sodium solution, the ratio Na:HfNCl and the reaction time. Pristine samples exhibiting low lithium intercalation degree upon electrochemical reduction gave the second stage as the major phase when treated with short reaction times or using low Na:HfNCl ratios, coexisting either with the host or with the first stage phase, whereas stage 1 is obtained as the major phase from pristine samples showing high electrochemical capacities. The staging behaviour and the multiphase nature of these samples account for the wide superconducting transitions and the different critical temperatures observed in these superconductors. [Copyright &y& Elsevier]

The crystal structure of the n = 1 member of the Ruddlesden-Popper family (SrO)(SrNbO2N)n was refined by the Rietveld method using neutron powder diffraction data. This complex crystallizes in the l4/mmm space group with cell parameters a = 4.0506(2) and c = 12.5936(9) Å. The refined composition was Sr2NbO3.28N0.72, which corresponds to a formal oxidation state for Nb of +4.72, meaning 72% Nb(V) and 28% Nb(IV). The nitrogen atoms order in the equatorial sites of the niobium octahedra according to Pauling's second crystal rule as the more charged anion occupies the site showing the larger bond strength sums. Pauling's second crystal rule is shown to be able to predict the distribution of anions in the available crystallographic sites in other mixed anion systems such as oxyhalides with K2NiF4 structures and other oxynitrides. The defect structure of the n = 1 and n = 2 members of the same family was investigated by high-resolution electron microscopy. Recurrent intergrowth along the c axis with other Ruddlesden-Popper members (n = 3, 4, and perovskite) is observed, resulting in streaking along this direction in the corresponding electron diffraction patterns. [ABSTRACT FROM AUTHOR]

α-HfNBr has been prepared at 760 °C in a sealed evacuated fused silica tube by reaction between NH4Br and Hf followed by purification through chemical vapour transport under a temperature gradient. The crystal structure of this compound at room temperature has been determined for the first time by Rietveld refinement of X-ray powder diffraction data, electron diffraction and high resolution electron microscopy. It crystallises in the orthorhombic space group Pmmn with the unit cell parameters a=4.1165(2), b=3.5609(2), c=8.6440(3) A˚. α-HfNBr is isotypic to FeOCl and is built from layers of composition Br&z.sbnd;Hf&z.sbnd;N&z.sbnd;N&z.sbnd;Hf&z.sbnd;Br stacked along c that are separated by a Van der Waals gap. The hafnium atoms are six-coordinated by four nitrogen atoms and two bromine atoms. The resulting coordination polyhedron may be described as a highly distorted octahedron. Electron diffraction and high resolution electron microscopy studies reveal that the material is almost free of defects in the inner part of the crystals and confirm the structural model refined by the Rietveld method. [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]

New oxynitrides of RZrO2N (R = Pr, Nd, and Sm) have been synthesized via a direct solid-state reaction of R2O3 with Zr2ON2 at 1200-1500° C under 2-3 GPa pressure. Powder X-ray diffraction shows that all three phases adopt an orthorhombic Pnma perovskite superstructure [a = 5.8537(1) Å, b = 8.1707(1) Å, and c = 5.7093(1) A for NdZrO2N] and the structural distortion increases with decreasing R3+ ionic radius. This method may enable new mixed-metal oxynitrides to be synthesized without the use of nitriding gas atmospheres. [ABSTRACT FROM AUTHOR]

Studies the synthesis and structures of two members of the family of Ruddlesden-Popper strontium niobium oxynitrides. X-ray and electron diffraction patterns of oxynitrides; Magnetic susceptibility for as-prepared and reduced sample of the oxynitrides; Averaged formal oxidation states for niobium; Crystal structure determination of the oxynitrides; Use of Rietveld analysis.

The article discusses the coupled colossal magneto-resistive and capacitive effects on a perovskite oxynitrides EuNbO2N. It highlights the synthesis done on the material to prove the earlier contentions raised. Furthermore, it reveals that there is an excellent potential magneto-responses in materials like EuNbO2N in combining the large EU 2+ spin and the off-center instability of Nb 5+ enhanced by bonding to nitride.

The title compound, obtained by treatment of NdVO4 in an NH3 flow (700 °C, 80 h), is characterized by powder X-ray and neutron diffraction, and by magnetic measurements. [ABSTRACT FROM AUTHOR]