Alkali and alkali–lead oxynitride phosphate glasses: a comparative structural study by NMR and XPS

Nitrided phosphate glasses are characterized by tetrahedral units P(O,N)₄ in which nitrogen atoms have substituted for both bridging and non-bridging double bonded oxygen atoms. ³¹P magic angle spinning (MAS) nuclear magnetic resonance (NMR) shows that PO₄, PO₃N and PO₂N₂ tetrahedra may coexist within the glass network. The relative proportion of these structural units as a function of the N/P ratio depends on the composition of the oxide base glass, as illustrated in sodium, lithium–sodium and lithium–sodium–lead phosphate glasses. Furthermore, ³¹P double quantum (DQ) MAS NMR shows that the nitrogen/oxygen substitution is not a random process. The modifier cations influence the connections between tetrahedra throughout the overall nitrided glass network, and, therefore, the final structure. N_1s X-ray photoelectron spectroscopy (XPS) shows that nitrogen atoms may exist in the P(O,N)₄ tetrahedra as doubly coordinated (–N= ) and triply coordinated (–N<) species, bonded to two and three phosphorus atoms, respectively. The relation between both kinds of nitrogen as a function of the N/P ratio depends also on the oxide-base glass composition. In this work, the thermal nitridation in flowing ammonia of alkali and alkali–lead metaphosphate glasses is studied. The results deduced from the NMR and XPS experiments make it possible, in addition to a comparison between the nitridation kinetics, to follow and to compare the structural evolution of oxynitride glasses resulting from a progressive nitrogen incorporation. In particular, the important role of PbO in the nitridation mechanism is revealed, demonstrating in this case that the nitridation is not random, its beginning included.     

Synthesis, Mo-valence state, thermal stability and thermoelectric properties of SrMoO3−xNx (x>1) oxynitride perovskites

Oxynitrides of the general composition SrMoO_3−xN_x (x>1) were synthesized by thermal ammonolysis of crystalline SrMoO₄. According to neutron and X-ray diffraction experiments, the materials crystallize in the cubic perovskite structure (space group Pm3¯m). X-ray absorption spectroscopy (XAS) shows evidence of local distortions of the Mo(O,N)₆ octahedra. The oxidation states of Mo determined by X-ray absorption near edge structure (XANES) spectroscopy are slightly lower than that calculated from the oxygen/nitrogen(O/N) content. The disagreement arises from the higher covalence of the Mo-N bonding when compared to the Mo-O bonding (“chemical shift”). The electrical transport properties of the samples are strongly different from SrMoO₃. It was found that the conductivity of the samples decreases with increasing nitrogen content. The Seebeck coefficient values are up to three times higher than those of SrMoO₃.     

Humidity effects in Fe16N2 fine powder preparation by low-temperature nitridation

Low-temperature nitridation has been reported to produce ferromagnetic α″-Fe₁₆N₂ by ammonia nitridation of α-Fe fine powder, which was obtained from the reduction of vapor-grown γ-Fe₂O₃. The effects of humidity during this preparation were investigated in the present study. α″-Fe₁₆N₂ was inconsistently obtained, and at low yield, from Fe₃O₄ fine powder (MT-40) prepared from aqueous solution. Reducing the adsorbed water content in the iron oxide starting powder resulted in improved reproducibility of the α″-Fe₁₆N₂ yield of the nitridation. The use of a smaller-diameter reaction tube, less than 25 mm in diameter, enabled more reproducible preparation from vapor-grown γ-Fe₂O₃ powder (CI-30). The reaction yield was further improved by using high-quality ammonia with a water content of ≤0.05 ppm. Minimizing the humidity made it possible to obtain a fine powder with a high α″-Fe₁₆N₂ content. Enhancement of the magnetization to 210 emu g⁻¹ at room temperature was observed from a nitrided mixture of α″-Fe₁₆N₂ with residual α-Fe, compared to 199 emu g⁻¹ for an α-Fe fine powder reduced from γ-Fe₂O₃. However, excess nitrogen and residual oxygen in the nitrided products reduced the magnetization below the value of α-Fe powder after nitridation. The magnetization was enhanced in nitrided products with a nitrogen content slightly below the stoichiometric amount for α″-Fe₁₆N₂.     

Effect of excitation states of nitrogen on the surface nitridation of iron and steel in d.c. glow discharge plasma

The plasma nitriding phenomena that occur on the surfaces of iron and steel were investigated. In particular, the correlation between the kinds of nitrogen radicals and the surface nitriding reaction was investigated using a glow‐discharge apparatus. To control the excitation of nitrogen radicals, noble gas mixtures were used for the plasma gas. The highly populated metastables of noble gases selectively produce excited nitrogen molecules (N₂*) or nitrogen molecule ions (N₂⁺). The optical emission spectra suggested that the formation of N₂*‐rich or N₂⁺‐rich plasma was successfully controlled by introducing different kinds of noble gases. Auger electron spectroscopy and XPS were used to characterize the depth profile of the elements and chemical species on the nitrided surface. The nitride layer formed by a N₂⁺‐rich plasma had a much higher nitrogen concentration than that by a N₂*‐rich plasma, likely due to the larger chemical activity of the N₂⁺ species as well as the N₂⁺ sputtering bombardment to the cathode surface. The strong reactivity of the N₂⁺ species was also confirmed from the chemical shift of N 1s spectra for iron nitrides. An iron nitride formed by the N₂⁺‐rich plasma has higher stoichiometric quantity of nitrogen than that formed by the N₂*‐rich plasma. Besides the effect of nitrogen radicals on surface nitridation, the contribution of the chromium in steel to the nitriding reaction was also examined. This chromium can promote a nitriding reaction at the surface, which results in an increase in the nitrogen concentration and the formation of nitride with high nitrogen coordination. Copyright © 2010 John Wiley & Sons, Ltd.     

Hydrothermal synthesis,characterization and photoluminescence property of a novel indium phosphate with 3D supramolecular structure

A one-dimensional chained indium phosphate In(H₂PO₄)(HPO₄)(C₁₀N₂H₈) (1) was synthesized under hydrothermal condition using 2,2′-bipyridine as a ligand and characterized by IR spectroscopy, ICP and elemental analyses, powder and single crystal X-ray diffraction analyses. Compound 1 crystallizes in the triclinic system, space group P-1. The connection of In-centered octahedra (InO₄N₂) and P-centered tetrahedra ({PO₃(OH)} and {PO₂(OH)₂}) constructs a new type of 1D chained structure with In/P ratio of 1/3. Interestingly, H₂PO₄ tetrahedron and 2,2′-bipyridine ligands "hanging" in the chain by bridging oxygen atoms and nitrogen atoms bond to the central In atoms. It is noted that the adjacent chains are stably packed together and the final structure exhibits interesting three-dimensional (3D) supramolecular array via π–π interactions of the 2,2′-bipyridine groups and hydrogen-bond interactions. Additionally, compound 1 shows strong photoluminescence property in the solid state at room temperature.     

New synthesis of excellent visible-light TiO2−xNx photocatalyst using a very simple method

An excellent visible-light-responsive (from 400 to 550 nm) TiO_2−xN_x photocatalyst was prepared by a simple wet method. Hydrazine was used as a new nitrogen resource in this paper. Self-made amorphous titanium dioxide precursor powders were dipped into hydrazine hydrate, and calcined at low temperature (110 °C) in the air. The TiO_2−xN_x was successfully synthesized, following by spontaneous combustion. The photocatalyst was characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), transmission electron microscope (TEM), UV-Vis diffuse reflectance spectrometer (DRS), and X-ray photoelectron spectroscopy (XPS). Analysis of XPS indicated that N atoms were incorporated into the lattice of the titania crystal during the combustion of hydrazine on the surface of TiO₂. Ethylene was selected as a target pollutant under visible-light excitation to evaluate the activity of this photocatalyst. The newly prepared TiO_2−xN_x photocatalyst with strong photocatalytic activity and high photochemical stability under visible-light irradiation was firstly demonstrated in the experiment.     

Enhanced visible-light absorption and dopant distribution of iodine-TiO2 nanoparticles synthesized by a new facile two-step hydrothermal method

In order to prepare visible-light responsive iodine-doped TiO₂, a new facile synthetic approach was proposed, which started with the cost-efficient and environmentally friendly precursor of undoped anatase TiO₂ to form nanotube structures as templates that collapsed and recrystallized into I-TiO₂ nanopowders in HIO₃ solution, followed by annealing at different temperatures. The modification of TiO₂ to incorporate iodine and form titanium dioxide with significantly enhanced absorption in the visible range of the spectrum was investigated. The extent of iodine dopant incorporation was determined by X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray analysis (EDX) and was found to be homogenously distributed on each nanostructure as determined by electron energy-loss spectroscopy (EELS) elemental mapping and EDX spectroscopy. The modified TiO₂ exhibits a dramatically extended absorption edge beyond 800 nm as compared to the original and unmodified TiO₂.     

Synthesis and structure of phosphates M<Subscript>0.5</Subscript>Ti<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>

Phosphates M_0.5Ti₂(PO₄)₃ (M = Ni, Zn) were synthesized by the sol-gel method and characterized by the methods of X-ray diffraction, IR spectroscopy, and electronic microprobe analysis. Structures of Ni_0.5Ti₂(PO₄)₃ and Zn_0.5Ti₂(PO₄)₃ were studied by Rietveld method using the X-ray powder diffraction data.     

An X-ray photoelectron spectroscopic study of novel SiON glasses

Novel SiON glasses obtained by melting mixtures of crystalline α-SiO₂ and α-Si₃N₄ were investigated by means of X-ray photoelectron spectroscopy (XPS). The incorporation of nitrogen into the SiO₂ network was recently proved by ²⁹Si-MAS-NMR (magic-angle spinning nuclear magnetic resonance) and Si K-XANES (X-ray absorption near edge structure). The Si 2p XPS and the Si KLL XAES (X-ray excited Auger electron spectroscopy) studies of the SiON glasses confirm the formation of mixed structural units (SiO_xN_4-x) by the presence of an additional spectral component energetically located between SiO₂- and Si₃N₄-like signals. The N 1s and O 1s XPS spectra support the conclusion about the incorporation of nitrogen into the SiO₂ network.     

Four new hydroxymonophosphates with closely related intersecting tunnels structures: The series AM(PO3(OH))2 with A=Rb, Cs; M=Fe, Al, Ga, In

The family of hydroxymonophosphates of generic formula AM^III(PO₃(OH))₂ has been revisited using hydrothermal techniques. Four new phases have been synthesized: CsIn(PO₃(OH))₂, RbFe(PO₃(OH))₂, RbGa(PO₃(OH))₂ and RbAl(PO₃(OH))₂. Single crystal diffraction studies show that they exhibit two different structural types from previously observed other phases with A=H₃O, NH₄, Rb and M=Al, V, Fe. The “Cs-In” and “Rb-Fe” phosphates crystallize in the triclinic space group , with the cell parameters a=7.4146(3) Å, b=9.0915(3) Å, c=9.7849(3) Å, α=65.525(3)°, β=70.201(3)°, γ=69.556(3)° and V=547.77(4) Å³ (Z=3) for CsIn(PO₃(OH))₂ and a=7.2025(4) Å, b=8.8329(8) Å, c=9.4540(8) Å, α=65.149(8)°, β=70.045(6)°, γ=69.591(6)° and V=497.44(8) Å³ (Z=3) for α-RbFe(PO₃(OH))₂. The “Rb-Al” and “Rb-Ga” phosphates crystallize in the Rc space group, with a=8.0581(18) Å and c=51.081(12) Å (V=2872.5(11) Å³ and Z=18) for RbAl(PO₃(OH))₂ and a=8.1188(15) Å and c=51.943(4) Å (V=2965(8) Å and Z=18) for RbGa(PO₃(OH))₂. These two structural types are closely related. Both are built up from M^IIIO6 octahedra sharing their apices with PO₃(OH) tetrahedra to form [M₃(PO₃OH)₆] units, but the latter exhibits a different configuration of their tetrahedra. The three-dimensional host-lattices result from the connection of the [M₃(PO₃OH)₆] units and they present numerous intersecting tunnels containing the monovalent cations.     

Direct measurement of the nitrogen content by XPS in self‐passivated TaNx thin films

The nitrogen content in tantalum nitride (TaN_x) thin films, where x indicates that TaN_x is not generally stoechiometric, can be measured directly by XPS. This is the purpose of the present study. However, the XPS spectra of TaN_x present electron energy loss spectroscopy (EELS) peaks that lead to a complex peak fitting, particularly for self‐passivated thin films. A complete peak fitting procedure based upon Tougaard's background, the Doniach‐Sunjic Function and EELS peaks, is presented. It is applied to two self‐passivated TaN_x thin films elaborated by reactive sputtering and presenting a different nitrogen content. The physical properties of these surfaces are interpreted in terms of Ta 4f_7/2 chemical states directly dependent on the nitrogen content. The main results are discussed and improvements are proposed to the method. Copyright © 2008 John Wiley & Sons, Ltd.     

XANES and XPS characterization of hard amorphous CSixNy thin films grown by RF nitrogen plasma assisted pulsed laser deposition

Amorphous carbon silicon nitride thin films were grown on (100) oriented silicon substrates by pulsed laser deposition (PLD) assisted by an RF nitrogen plasma source. Up to about 30 at. % nitrogen and up to 20 at. % silicon were found in the hard amorphous thin films by XPS in dependence on the composition of the mixed graphite / Si₃N₄ PLD target. The universal nanohardness was measured to be at maximum load force of 0.1 mN up to 23 GPa for thin CSi_xN_y films with reference value of 14 GPa for single crystalline silicon. X-ray photoelectron spectroscopy (XPS) of CSi_xN_y film surfaces showed a clear correlation of binding energy and intensity of fitted features of N 1s, C 1s, and Si 2p peaks to the composition of the graphite / Si₃N₄ target and to nitrogen flow through the plasma source, indicating soft changes of binding structure of the thin films due to variation of PLD parameters. Auger electron spectroscopy (AES) of Si KL₂₃L₂₃;¹D Auger transition gave a detailed view of bonding structure of Si in the CSi_xN_y films. The intensity of π* and σ* resonances at the carbon K-edge X-ray absorption near-edge structure (XANES) of the CSi_xN_y films measured at BESSY I corresponded to the nanohardness of the CSi_xN_y films, thus giving insight into chemical binding structure of superhard amorphous materials.     

A boundary for reaction mechanisms within the transition metals interacting with nitrogen oxides is observed in DSIMS experiments

Summary Dynamic secondary ion mass spectrometry (DSIMS) investigations have been carried out with Cr, Mn, Fe, Co, Mo, Rh, W, Re, Os and Ir under 4 mPa N₂O, NO and 3 mPa NO₂ as reactant gases. Results indicate similar behaviour in adsorption for Cr, Mn, Fe, Mo, W on the one hand and for Co, Rh, Os and Ir on the other. For the first group of metals the nitrogen oxide molecules are always totally destroyed in adsorption whereas the second group shows evidence for surface compounds such as MeNO (Me=metal) indicating only a partial dissociation in the case of N₂O and NO₂, and molecular adsorption under NO respectively. Re does not belong uniquely to either group because it reacts with N₂O and NO₂ dissociatively whereas under NO only partial dissociation is observed.Abbreviations SIMS Secondary ion mass spectrometry - SSIMS Static SIMS - AES Auger electron spectroscopy - EELS Electron energy-loss spectroscopy - LEED Low energy electron diffraction - TDS Thermal desorption spectroscopy - XPS, UPS X-ray/Ultraviolet photoelectron spectroscopy     

Structure,optical and magnetic properties of LaFeO3 nanoparticles prepared by polymerized complex method

This work reports the study the structure, optical and magnetic properties of LaFeO₃ nanoparticles synthesized by the polymerized complex method. The LaFeO₃ nanoparticles were successfully obtained from calcination of the precursor at different temperatures from 750 to 1,050 °C in air for 2 h. The calcined LaFeO₃ nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV–Visible spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge spectroscopy (XANES) and vibrating sample magnetometry. The XRD and TEM results showed that all LaFeO₃ samples had a single phase nature with the orthorhombic structure. The estimated crystallite sizes were in the range of 44.5 ± 2.4–74.1 ± 4.9 nm. UV–Vis spectra showed strong UV and Vis absorption with small band gap energy. The valence states of Fe ions were in the Fe³⁺ and Fe⁴⁺ state, as confirmed by XPS and XANES results. The weak ferromagnetic behavior with specific saturation magnetization of 0.1 emu/g at 10 kOe was obtained for the small particle of 44.5 ± 2.4 nm. The uncompensated spins at the surface was proposed as playing a part in the magnetic properties of small sized LaFeO₃.     

The tribological behaviours of dithiocarbamate‐triazine derivatives as additives in mineral oil

Ashless and non‐phosphorus hydroxyl‐containing dithiocarbamate‐triazine compounds,2,4,6‐tri[N,N‐di‐i‐octyldithiocarmate‐(2′‐hydroxyl)‐propionylthio]‐1,3,5‐s‐triazine (LDION) were prepared and their tribological behaviour as additives in mineral oil were evaluated using a four‐ball tester. Thermal degradation tests were conducted to identify their thermal stabilities using a thermo‐gravimetric analyser. The worn surfaces were investigated by X‐ray photoelectron spectroscopy (XPS) and X‐ray absorption near edge structure (XANES) spectroscopy. The results indicate that the additive LDION possesses high thermal stabilities and good load‐carrying capacities. Moreover, it has good anti‐wear property at all test concentration and under all test loads. The results of XPS and XANES analyses illustrate that the prepared compounds as additives in mineral oil forms a protective film containing oxidised compounds and organic nitrogen‐containing compounds and inorganic sulfate on the metal surface during sliding process. Copyright © 2008 John Wiley & Sons, Ltd.     

Characterization of transition metal nitride formation in rapid thermal processing (RTP)

The potential of RTP for the preparation of transition metal nitrides by reaction of metal thin films in molecular nitrogen was investigated. The films and the nitridation process were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), energy dispersive x-ray analysis (EDX) in a scanning electron microscope (SEM) and secondary neutral mass spectrometry (SNMS). The chemical states of vanadium at the utmost surface, detected by XPS, are related to V₂O₅ before RTP and to vanadium nitride, oxide and oxynitride after RTP. The deposition of a 3 nm Si top layer prevents V from oxidation and its selective removal before RTP enhances the proportion of nitride determined by XPS after RTP. From comparative experiments in a conventional tube furnace the advantages of RTP became obvious. With short process times of the RTP technique the integral amount of residual oxygen is kept low and oxide formation is largely avoided. The nitrogen content and the different polycrystalline phases formed by varying process time and temperature provide information about reactivity and the nitridation process. The nitrogen to vanadium ratio was determined by EDX and SNMS, revealing that the N content reaches saturation after only 5 seconds at 1100?°C.     

Valence state of elements on the Fe—Ru catalyst surface treated in various media

X-ray photoelectron spectroscopy (XPS) is used to show that Fe and Ru on the catalyst surface virtually completely transform into the metallic state during the reduction of the Fe-Ru catalyst. Analysis of the spectra of nitrogen, which is present in the reduced and activated Fe-Ru catalyst, showed the presence of three Nls signals with the binding energies 400.4, 398.6, and 397.4 eV. These bands are assigned to three nitrogen states: NH₃, NH and/or NH₂, and N₂ (or one of the forms of molecular nitrogen, which is a precursor of dissociation), respectively     

A Vanadium (V) Hydroxymonophosphate Hydrate with a “Tape-Like” structure: K3(VO2)2PO4PO3OH·H2O

A new vanadium (V) hydroxymonophosphate hydrate, K₃(VO₂)₂PO₄PO₃OH·H₂O, with a “tape-like” structure has been synthesized. This compound crystallizes in the space group P2₁/c with a=5.099(1) Å, b=29.168(3) Å, c=8.115(1) Å, β=91.65(1)°. Its structure consists of [V₂P₂O₁₁OH]_∞ ribbons built up of corner-sharing VO₅ pyramids, PO₄, and PO₃OH tetrahedra, interleaved with K⁺ ions and H₂O molecules. In spite of its unidimensional character, this structure forms pentagonal tunnels. Relationships with frameworks involving tetragonal tunnels are studied.     

π-facial interactions between Cl and [S4N3]. X-ray crystal structure of [S4N3]Cl

The X-ray structure of [S₄N₃]Cl reveals three independent molecules, which all display π-facial interactions between the Cl⁻ and the pseudo-aromatic [S₄N₃]⁺ rings to produce a structure containing “inverse sandwich” systems.     

Synthesis and solid-state structural characterization of di-μ-azido-bis[{azido(N,N-diethylethylenediamine)}copper(II)]

Summary The 11 mixed-ligand [{Cu(N₃)₂(diEten)}₂] (diEten=N,N-diethylethylenediamine) complex has been synthesized and characterized by i.r. spectroscopy and X-ray diffraction. The compound crystallizes in the triclinic space group P1. Its structure consists of a centrosymmetric Cu₂N₂ unit whose N atoms belong to end-on azido bridges. Each copper atom is also surrounded by three nitrogen atoms; two from oneN, N-diethylethylenediamine, and one from the remaining azide. The five nitrogen atoms altogether occupy the vertices of a slightly distorted trigonal bipyramid, and the azidobridges produced a rather short Cu...Cu distance of 3.37 Å.