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Stefan G. Ebbinghaus - One of the best experts on this subject based on the ideXlab platform.
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photocatalytic properties of coox loaded nano crystalline perovskite Oxynitrides abo2n a ca sr ba la b nb ta
ChemInform, 2016Co-Authors: Florian Oehler, Stefan G. EbbinghausAbstract:Abstract Highly crystalline niobium- and tantalum-based oxynitride perovskite nanoparticles were obtained from hydrothermally synthesized oxide precursors by thermal ammonolysis at different temperatures. The samples were studied with respect to their morphological, optical and thermal properties as well as their photocatalytic activity in the decomposition of methyl orange. Phase pure Oxynitrides were obtained at rather low ammonolysis temperatures between 740 °C (CaNbO2N) and 1000 °C (BaTaO2N). Particle sizes were found to be in the range 27 nm–146 nm and large specific surface areas up to 37 m2 g−1 were observed. High photocatalytic activities were found for CaNbO2N and SrNbO2N prepared at low ammonolysis temperatures. CoOx as co-catalyst was loaded on the oxynitride particles resulting in a strong increase of the photocatalytic activities up to 30% methyl orange degradation within 3 h for SrNbO2N:CoOx.
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perovskite related Oxynitrides recent developments in synthesis characterisation and investigations of physical properties
Progress in Solid State Chemistry, 2009Co-Authors: Stefan G. Ebbinghaus, Armin Reller, Hanspeter Abicht, Richard Dronskowski, Thomas Muller, Anke WeidenkaffAbstract:Abstract Since the first investigations of perovskite type Oxynitrides with the generalised composition ABO3−xNx about twenty years ago, these compounds have become of growing interest. The incorporation of nitride ions in the perovskite lattice results in distinct changes in the electronic structure leading to unusual physical properties. In this article we report on new synthesis techniques, different analytical methods, progress in the structural characterisation by comprehensive diffraction techniques and local spectroscopic methods like XAS and NMR as well as state of the art theoretical investigations. Various physical characteristics like electrical and thermal transport parameters and dielectric properties are described. The thermal and chemical stability of oxynitride perovskites are investigated and their applications in different photocatalytic reactions are discussed.
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Thermal oxidation of oxynitride perovskites in different atmospheres
Thermochimica Acta, 2008Co-Authors: Rosiana Aguiar, D. Logvinovich, Anke Weidenkaff, Armin Reller, Stefan G. EbbinghausAbstract:Abstract Oxynitride perovskites with bright and variable colour have the potential to be employed as non-toxic pigments, and to substitute colourants that contain harmful heavy metals. For this application it is extremely important to have a precise knowledge about the materials stability. The thermal stability of oxynitride perovskites in different atmospheres was measured by thermogravimetry in combination with mass spectroscopy (MS). The studied compounds, namely LaTiO2N, SrNbO2N and SrTaO2N, were heated up to 1200 °C in argon–oxygen mixtures with varying oxygen contents. It was found that the thermal behaviour of the studied Oxynitrides changes drastically with the oxygen concentration. When heated up in pure argon the Oxynitrides transform to oxides containing transition metals of lower oxidation state and/or binary nitrides. For oxygen contents between 0.5% and 20% the samples were completely oxidised. The oxidation rate increases with oxygen content. MS analysis of the gaseous products (including N2, NO and NO2) reveals a complex reaction mechanism, which is strongly modified by the composition of the atmosphere.
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synthesis and properties of Oxynitrides la sr ti o n 3 thin films
Progress in Solid State Chemistry, 2007Co-Authors: Rosiana Aguiar, Anke Weidenkaff, Armin Reller, C W Schneider, Stefan G. EbbinghausAbstract:Abstract We report on the synthesis, optical and electrical properties of thin films of LaxSr(1−x)Ti(O,N)3, x = 0, 0.25, 0.50, 0.75 and 1. The films were grown by a soft chemistry process from polymeric precursor solutions, which were deposited by spin coating on 〈100〉-oriented SrTiO3 substrates. After drying, the organic matrix was burned at 400 °C. These steps were repeated six times to obtain a reasonable thickness of the films. Afterwards, the samples were heated in a tube furnace at 950 °C in flowing ammonia. The oxynitride films showed different colours from red-orange for LaTiO2N to greenish-blue for SrTiO3:N. The films were characterised by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy, secondary ion mass spectrometry and electrical measurements. The results show that the films are polycrystalline and have the perovskite structure. Their thickness is about 440 nm and the average roughness value is 7.5 nm. UV–vis transmittance measurements showed a strong decrease in the band gap values for the Oxynitrides compared to the respective oxides. The values change from approximately 3.2 eV for the oxides to an average value of 2.4 eV for the Oxynitrides. The electrical measurements indicate a change in the electrical behaviour from insulator for LaTiO2N to semiconductor for SrTiO3:N.
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tantalum and niobium perovskite Oxynitrides synthesis and analysis of the thermal behaviour
Thermochimica Acta, 2005Co-Authors: Anita Rachel, Anke Weidenkaff, Stefan G. Ebbinghaus, Martin Gungerich, Peter J Klar, Jan Hanss, Armin RellerAbstract:Abstract Ta 5+ and Nb 5+ -based oxynitride perovskites of the ABO 2 N type (A = Ca, Sr, Ba) were synthesised by ammonolysis of complex oxide precursors. These precursors were either crystalline perovskites or amorphous xerogels prepared by solid–solid reaction and by soft chemistry methods, respectively. Phase purity of the Oxynitrides was verified by X-ray diffraction (XRD) and their crystal structures were determined by Rietveld refinements. The morphology of the obtained powders was characterised by scanning electron microscopy (SEM). Thermal stability was investigated by thermogravimetric analysis (TGA) coupled with mass spectroscopy. Oxidation studies reveal an intermediate product that gives rise to a characteristic weight gain in the TG curve. This intermediate was found for all the examined Oxynitrides in oxidising atmosphere. Investigations by Raman scattering revealed the presence of dinitrogen (N N) loosely bound to B and N B bonds (B = transition metal) in the intermediate compounds. Mass spectral analysis confirmed molecular nitrogen evolution indicating that N 2 is retained during the oxidation reaction. At higher temperatures ( T = 800–1000 °C) the dinitrogen is released leading to the formation of the corresponding oxides.
Kazunari Domen - One of the best experts on this subject based on the ideXlab platform.
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Perovskite Sr_1−x Ba_ x W_1−y Ta_ y (O,N)_3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light
Materials for Renewable and Sustainable Energy, 2017Co-Authors: Kenta Kawashima, Kazunari Domen, Ralf Riedel, Mirabbos Hojamberdiev, Christina Stabler, Dragoljub Vrankovic, Kunio Yubuta, Katsuya TeshimaAbstract:To study the effect of partial Ba^2+-to-Sr^2+ and/or Ta^5+-to-W^4–6+ substitution on various properties of SrW(O,N)_3, cubic perovskite-type W- and/or Ta-based Oxynitrides Sr_1− x Ba_ x W_1− y Ta_ y (O,N)_3, where x , y = 0,0; 0.25,0; 0.125,0.125; 0,0.25; and 1.1, were synthesized by ammonolyzing their corresponding oxide precursors under an NH_3 flow. The synthesized Oxynitrides have highly porous structures and consist of small crystallites in the range of 53–630 nm and with specific surface areas in the range of 5.4–14.7 m^2·g^−1. Interestingly, the Ta^5+-to-W^4~6+ substitution in SrW(O,N)_3 can suppress the formation of reduced tungsten species during thermal ammonolysis. The weaker absorptions beyond 560 and 580 nm in the UV–Vis diffuse reflectance spectra, which correspond to reduced tungsten species, are observed in SrW_0.75Ta_0.25(O,N)_3 and Sr_0.875Ba_0.125W_0.875Ta_0.125(O,N)_3 compared to SrW(O,N)_3 and Sr_0.75Ba_0.25W(O,N)_3. The XPS results reveal that low-valent transition metal oxides, nitrides, and Oxynitrides and/or tungsten metal are present on the surfaces of the as-synthesized Oxynitrides. After 5 h of the photocatalytic oxygen evolution reaction, CoO_ x -loaded SrW_0.75Ta_0.25(O,N)_3 exhibited the highest amount of evolved O_2 gas due to its higher specific surface area and lower concentration of intrinsic defects. During the photocatalytic reaction, the N_2 gas is also evolved because of the self-oxidation of Oxynitrides consuming photo-generated holes. The estimated TONs of the oxynitride samples exceeded one, evidencing that the observed O_2 gas evolution reactions were catalytic. Accordingly, the photostability enhancement of Oxynitrides reduces the loss of photo-generated charge carriers and increases their photocatalytic activity. Graphical abstract
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Perovskite Sr1−x Ba x W1−y Ta y (O,N)3: synthesis by thermal ammonolysis and photocatalytic oxygen evolution under visible light
SpringerOpen, 2017Co-Authors: Kenta Kawashima, Kazunari Domen, Ralf Riedel, Mirabbos Hojamberdiev, Christina Stabler, Dragoljub Vrankovic, Kunio Yubuta, Katsuya TeshimaAbstract:Abstract To study the effect of partial Ba2+-to-Sr2+ and/or Ta5+-to-W4–6+ substitution on various properties of SrW(O,N)3, cubic perovskite-type W- and/or Ta-based Oxynitrides Sr1−x Ba x W1−y Ta y (O,N)3, where x,y = 0,0; 0.25,0; 0.125,0.125; 0,0.25; and 1.1, were synthesized by ammonolyzing their corresponding oxide precursors under an NH3 flow. The synthesized Oxynitrides have highly porous structures and consist of small crystallites in the range of 53–630 nm and with specific surface areas in the range of 5.4–14.7 m2·g−1. Interestingly, the Ta5+-to-W4~6+ substitution in SrW(O,N)3 can suppress the formation of reduced tungsten species during thermal ammonolysis. The weaker absorptions beyond 560 and 580 nm in the UV–Vis diffuse reflectance spectra, which correspond to reduced tungsten species, are observed in SrW0.75Ta0.25(O,N)3 and Sr0.875Ba0.125W0.875Ta0.125(O,N)3 compared to SrW(O,N)3 and Sr0.75Ba0.25W(O,N)3. The XPS results reveal that low-valent transition metal oxides, nitrides, and Oxynitrides and/or tungsten metal are present on the surfaces of the as-synthesized Oxynitrides. After 5 h of the photocatalytic oxygen evolution reaction, CoO x -loaded SrW0.75Ta0.25(O,N)3 exhibited the highest amount of evolved O2 gas due to its higher specific surface area and lower concentration of intrinsic defects. During the photocatalytic reaction, the N2 gas is also evolved because of the self-oxidation of Oxynitrides consuming photo-generated holes. The estimated TONs of the oxynitride samples exceeded one, evidencing that the observed O2 gas evolution reactions were catalytic. Accordingly, the photostability enhancement of Oxynitrides reduces the loss of photo-generated charge carriers and increases their photocatalytic activity. Graphical abstrac
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A novel oxynitride photocatalyst system for water splitting : La2Zn1-xTi1+x(O,N)6
2012Co-Authors: Vincent Michel, Franck Tessier, Kazuhiko Maeda, François Cheviré, Xavier Rocquefelte, Stéphane Jobic, Kazunari DomenAbstract:The use of solar energy is of highest interest from a low environmental impact viewpoint, and nowadays the photocatalytic splitting of water under solar radiations is a challenging and promising domain of research to provide clean and renewable H2 as an alternative energy resource [1]. Current oxide photocatalysts (TiO2 , ZnO, SrTiO3 , NaTaO3 ...) are wide-gap semiconductors for which UV-light is necessary to produce electron-hole pairs by photoexcitation. Therefore, the development of visible-light-driven photocatalysts for overall water splitting is currently attracting much attention as a potential efficient utilization of solar energy. So far the (oxy)nitride approach become attractive and promising for this specific issue as a consequence of the anionic N3-/O2- substitution results in an increase of the covalent character which is illustrated by a shift of the absorption edge towards higher wavelength values (band gap < 3 eV). However other requirements have to be considered to synthesize an efficient visible-light-driven photocatalyst such as the mobility of the photogenerated charge carriers, the crystal structure or the chemical stability. Perovskite-type Oxynitrides containing lanthanides and d0 metal ions such as LaTiO2N exhibit interesting photocatalytic behavior as well as d10-type metal Oxynitrides and sulfides, for instance (Zn,Ga)(O,N) and ZnS systems. Here, we have investigated a system combining these features: the monoclinic perovskite-type oxynitride system La2Zn1-xTi1+x(O,N)6. It is expected that the expanded nature of the Zn 4s band improves the mobility of the photogenerated carriers thus enhancing the photocatalytic activity of the material [2]. The effect of the Zn/Ti ratio on the photocatylic behavior of the oxynitride is investigated and the performance of this new photocatalyst will be compared to the reference material LaTiO2N. REFERENCES 1. K. Maeda, J. Photochem. Photobiol. C: Photochem. Reviews 58-59 (2011) p. 443-446 2. J. Yin, Z. Zou, J. Ye, J. Phys. Chem. B 108 (2004) p. 12790-12794
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Oxynitride materials for solar water splitting.
MRS Bulletin, 2011Co-Authors: Kazuhiko Maeda, Kazunari DomenAbstract:Water splitting to form hydrogen and oxygen over a heterogeneous photocatalyst using solar energy is a promising process for clean and renewable hydrogen production. In recent years, numerous attempts have been made for the development of photocatalysts that work under visible light irradiation to efficiently utilize solar energy. This article reviews recent research progress in the development of visible light-driven photocatalysts, focusing on the refinement of oxynitride materials. They harvest visible photons (~450–700 nm) and work as stable photocatalysts for water reduction and oxidation under visible light. Oxynitrides with d 0 electronic configuration can be successfully applied to a two-step water-splitting system, which can harvest a wide range of visible photons (~660 nm), in the presence of an iodate/iodide shuttle redox mediator. Also d 10 -type Oxynitrides of GaN–ZnO and ZnGeN 2 –ZnO solid solutions can achieve functionality as photocatalysts for overall water-splitting under visible light without noticeable degradation.
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synthesis and photocatalytic activity of perovskite niobium Oxynitrides with wide visible light absorption bands
Chemsuschem, 2011Co-Authors: Bhavin Siritanaratkul, Kazuhiko Maeda, Takashi Hisatomi, Kazunari DomenAbstract:Photocatalytic activities of perovskite-type niobium Oxynitrides (CaNbO2N, SrNbO2N, BaNbO2N, and LaNbON2) were examined for hydrogen and oxygen evolution from water under visible-light irradiation. These niobium Oxynitrides were prepared by heating the corresponding oxide precursors, which were synthesized using the polymerized complex method, for 15 h under a flow of ammonia. They possess visible-light absorption bands between 600–750 nm, depending on the A-site cations in the structures. The oxynitride CaNbO2N, was found to be active for hydrogen and oxygen evolution from methanol and aqueous AgNO3, respectively, even under irradiation by light at long wavelengths (λ<560 nm). The nitridation temperature dependence of CaNbO2N was investigated and 1023 K was found to be the optimal temperature. At lower temperatures, the oxynitride phase is not adequately produced, whereas higher temperatures produce more reduced niobium species (e. g., Nb3+ and Nb4+), which can act as electron-hole recombination centers, resulting in a decrease in activity.
Franck Tessier - One of the best experts on this subject based on the ideXlab platform.
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Titanium and vanadium oxynitride powders as pseudo-capacitive materials for electrochemical capacitors
Electrochimica Acta, 2012Co-Authors: R. Lucio Porto, Franck Tessier, R. Frappier, J.b. Ducros, C. Aucher, H. Mosqueda, Sébastien Chenu, B. Chavillon, François CheviréAbstract:TiOxNy and VOxNy powders have been synthesized using oxide precursors and a conventional nitridation method. It enables to control of oxygen content and surface area. The electrochemical performances of the different powders have been investigated. A strong dependence on the surface area as well as on the nature of the oxynitride has been found. A typical value of 300 μF cm−2 has been determined for VOxNy powders, while TiOxNy powders only show 50 μF cm−2. In this last case it is believed that only double layer capacitance or weak redox reactions participate in charge storage mechanism while for vanadium based Oxynitrides, a thin layer below the surface (≈4 Å) is involved in charge storage via faradic reactions. VOxNy electrodes can be operated in different aqueous electrolytes, but only double layer capacitance is measured in neutral electrolytes. The highest capacitance values (≈80 F g−1) are measured in KOH and fair cycling ability is achieved when the electrochemical window is limited, thus avoiding oxidative potentials.
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A novel oxynitride photocatalyst system for water splitting : La2Zn1-xTi1+x(O,N)6
2012Co-Authors: Vincent Michel, Franck Tessier, Kazuhiko Maeda, François Cheviré, Xavier Rocquefelte, Stéphane Jobic, Kazunari DomenAbstract:The use of solar energy is of highest interest from a low environmental impact viewpoint, and nowadays the photocatalytic splitting of water under solar radiations is a challenging and promising domain of research to provide clean and renewable H2 as an alternative energy resource [1]. Current oxide photocatalysts (TiO2 , ZnO, SrTiO3 , NaTaO3 ...) are wide-gap semiconductors for which UV-light is necessary to produce electron-hole pairs by photoexcitation. Therefore, the development of visible-light-driven photocatalysts for overall water splitting is currently attracting much attention as a potential efficient utilization of solar energy. So far the (oxy)nitride approach become attractive and promising for this specific issue as a consequence of the anionic N3-/O2- substitution results in an increase of the covalent character which is illustrated by a shift of the absorption edge towards higher wavelength values (band gap < 3 eV). However other requirements have to be considered to synthesize an efficient visible-light-driven photocatalyst such as the mobility of the photogenerated charge carriers, the crystal structure or the chemical stability. Perovskite-type Oxynitrides containing lanthanides and d0 metal ions such as LaTiO2N exhibit interesting photocatalytic behavior as well as d10-type metal Oxynitrides and sulfides, for instance (Zn,Ga)(O,N) and ZnS systems. Here, we have investigated a system combining these features: the monoclinic perovskite-type oxynitride system La2Zn1-xTi1+x(O,N)6. It is expected that the expanded nature of the Zn 4s band improves the mobility of the photogenerated carriers thus enhancing the photocatalytic activity of the material [2]. The effect of the Zn/Ti ratio on the photocatylic behavior of the oxynitride is investigated and the performance of this new photocatalyst will be compared to the reference material LaTiO2N. REFERENCES 1. K. Maeda, J. Photochem. Photobiol. C: Photochem. Reviews 58-59 (2011) p. 443-446 2. J. Yin, Z. Zou, J. Ye, J. Phys. Chem. B 108 (2004) p. 12790-12794
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Novel TaPO5-xN2x/3 Oxynitrides
Journal of Alloys and Compounds, 2012Co-Authors: Erwan Ray, Franck Tessier, François Cheviré, Nathalie Herbert, Ronan Lebullenger, Claire Roiland, Bruno BureauAbstract:A series of novel nitrided tantalophosphates has been prepared by nitridation of X-ray amorphous TaPO5 precursors under ammonia flow. By varying the nitridation temperature, amorphous TaPO5-xN2x/3 (1.6 < x < 4.1) Oxynitrides were obtained with different nitrogen contents (N wt.% = 5-15). The most relevant features of this oxynitride series are as follow: (i) specific surface areas higher than 150 m2.g−1, (ii) yellow to orange colors depending on nitrogen contents and (iii) formation of a solid solution with variable nitrogen and oxygen contents. The precursors and corresponding Oxynitrides have been characterized by several techniques including X-ray diffraction, oxygen/nitrogen elemental analyses, BET analysis, UV-vis spectrophotometry, thermal analysis, SEM, DRIFT and NMR analyses.
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Structural study of gallium Oxynitrides prepared by ammonolysis of different oxide precursors
Journal of Physics D: Applied Physics, 2009Co-Authors: Xavier Cailleaux, Franck Tessier, Odile Merdrignac-conanec, María Del Carmen Marco De Lucas, Kazuteru Nagasaka, Shinichi KikkawaAbstract:A comparative structural study has been carried out on gallium oxynitride powders using XRD and Raman spectroscopy. Gallium Oxynitrides have been prepared by ammonolysis of either NiGa2O4 ternary oxide or the citrate method-derived amorphous oxide. Their crystal chemistry is different and appears to be influenced by the nature of the oxide precursor: whereas gallium oxynitride obtained from amorphous gallium oxide crystallizes with the common wurtzite structure, gallium oxynitride obtained from NiGa2O4 crystallizes with an original structure that we have identified as the carborundum II (B6) structure type or 6H-SiC. As far as we know, this is the first 6H-SiC structure found in gallium oxynitride powders.
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Crystal structure and optical properties of oxynitride rare-earth tantalates RTa-(O, N) (R = Nd, Gd, Y)
Materials Research Bulletin, 2008Co-Authors: Shinichi Kikkawa, Takashi Takeda, Akira Yoshiasa, Pascal Maillard, Franck TessierAbstract:X-ray absorption and photoluminescence were used to investigate the structure of rare-earth tantalum Oxynitrides RTa-(O, N) (R = Nd, Gd, Y). Owing to the size of the rare-earth element, the crystal structure tends towards the pyrochlore or defect fluorite-type structure. EXAFS suggested neodymium and yttrium atoms are coordinated either by 6 + 2 or 6 oxygen/nitrogen atoms in the Nd or Y respective Oxynitrides although the coordination number of tantalum is six in both compounds. Photoluminescence for 5 at.% doped europium showed the spectra compatible with the point symmetry C3v lower than Oh in fluorite and D3d in pyrochlore structure type for both the Gd and Y tantalum Oxynitrides. These measurements supported that their structure types were basically pyrochlore for Nd and Gd tantalum Oxynitrides and defect fluorite for Y tantalum oxynitride but they are highly defective.
Armin Reller - One of the best experts on this subject based on the ideXlab platform.
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perovskite related Oxynitrides recent developments in synthesis characterisation and investigations of physical properties
Progress in Solid State Chemistry, 2009Co-Authors: Stefan G. Ebbinghaus, Armin Reller, Hanspeter Abicht, Richard Dronskowski, Thomas Muller, Anke WeidenkaffAbstract:Abstract Since the first investigations of perovskite type Oxynitrides with the generalised composition ABO3−xNx about twenty years ago, these compounds have become of growing interest. The incorporation of nitride ions in the perovskite lattice results in distinct changes in the electronic structure leading to unusual physical properties. In this article we report on new synthesis techniques, different analytical methods, progress in the structural characterisation by comprehensive diffraction techniques and local spectroscopic methods like XAS and NMR as well as state of the art theoretical investigations. Various physical characteristics like electrical and thermal transport parameters and dielectric properties are described. The thermal and chemical stability of oxynitride perovskites are investigated and their applications in different photocatalytic reactions are discussed.
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Thermal oxidation of oxynitride perovskites in different atmospheres
Thermochimica Acta, 2008Co-Authors: Rosiana Aguiar, D. Logvinovich, Anke Weidenkaff, Armin Reller, Stefan G. EbbinghausAbstract:Abstract Oxynitride perovskites with bright and variable colour have the potential to be employed as non-toxic pigments, and to substitute colourants that contain harmful heavy metals. For this application it is extremely important to have a precise knowledge about the materials stability. The thermal stability of oxynitride perovskites in different atmospheres was measured by thermogravimetry in combination with mass spectroscopy (MS). The studied compounds, namely LaTiO2N, SrNbO2N and SrTaO2N, were heated up to 1200 °C in argon–oxygen mixtures with varying oxygen contents. It was found that the thermal behaviour of the studied Oxynitrides changes drastically with the oxygen concentration. When heated up in pure argon the Oxynitrides transform to oxides containing transition metals of lower oxidation state and/or binary nitrides. For oxygen contents between 0.5% and 20% the samples were completely oxidised. The oxidation rate increases with oxygen content. MS analysis of the gaseous products (including N2, NO and NO2) reveals a complex reaction mechanism, which is strongly modified by the composition of the atmosphere.
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synthesis and properties of Oxynitrides la sr ti o n 3 thin films
Progress in Solid State Chemistry, 2007Co-Authors: Rosiana Aguiar, Anke Weidenkaff, Armin Reller, C W Schneider, Stefan G. EbbinghausAbstract:Abstract We report on the synthesis, optical and electrical properties of thin films of LaxSr(1−x)Ti(O,N)3, x = 0, 0.25, 0.50, 0.75 and 1. The films were grown by a soft chemistry process from polymeric precursor solutions, which were deposited by spin coating on 〈100〉-oriented SrTiO3 substrates. After drying, the organic matrix was burned at 400 °C. These steps were repeated six times to obtain a reasonable thickness of the films. Afterwards, the samples were heated in a tube furnace at 950 °C in flowing ammonia. The oxynitride films showed different colours from red-orange for LaTiO2N to greenish-blue for SrTiO3:N. The films were characterised by X-ray diffraction, scanning electron microscopy, atomic force microscopy, UV–vis spectroscopy, secondary ion mass spectrometry and electrical measurements. The results show that the films are polycrystalline and have the perovskite structure. Their thickness is about 440 nm and the average roughness value is 7.5 nm. UV–vis transmittance measurements showed a strong decrease in the band gap values for the Oxynitrides compared to the respective oxides. The values change from approximately 3.2 eV for the oxides to an average value of 2.4 eV for the Oxynitrides. The electrical measurements indicate a change in the electrical behaviour from insulator for LaTiO2N to semiconductor for SrTiO3:N.
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tantalum and niobium perovskite Oxynitrides synthesis and analysis of the thermal behaviour
Thermochimica Acta, 2005Co-Authors: Anita Rachel, Anke Weidenkaff, Stefan G. Ebbinghaus, Martin Gungerich, Peter J Klar, Jan Hanss, Armin RellerAbstract:Abstract Ta 5+ and Nb 5+ -based oxynitride perovskites of the ABO 2 N type (A = Ca, Sr, Ba) were synthesised by ammonolysis of complex oxide precursors. These precursors were either crystalline perovskites or amorphous xerogels prepared by solid–solid reaction and by soft chemistry methods, respectively. Phase purity of the Oxynitrides was verified by X-ray diffraction (XRD) and their crystal structures were determined by Rietveld refinements. The morphology of the obtained powders was characterised by scanning electron microscopy (SEM). Thermal stability was investigated by thermogravimetric analysis (TGA) coupled with mass spectroscopy. Oxidation studies reveal an intermediate product that gives rise to a characteristic weight gain in the TG curve. This intermediate was found for all the examined Oxynitrides in oxidising atmosphere. Investigations by Raman scattering revealed the presence of dinitrogen (N N) loosely bound to B and N B bonds (B = transition metal) in the intermediate compounds. Mass spectral analysis confirmed molecular nitrogen evolution indicating that N 2 is retained during the oxidation reaction. At higher temperatures ( T = 800–1000 °C) the dinitrogen is released leading to the formation of the corresponding oxides.
Yuji Masubuchi - One of the best experts on this subject based on the ideXlab platform.
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environmentally benign synthesis and color tuning of strontium tantalum perovskite oxynitride and its solid solutions
Inorganic Chemistry, 2021Co-Authors: Takuya Sakata, Risa Yoshiyuki, Ryoki Okada, Sohta Urushidani, Naoki Tarutani, Kiyofumi Katagiri, Kei Inumaru, Kyohei Koyama, Yuji MasubuchiAbstract:A facile method was successfully developed to prepare strontium-tantalum perovskite oxynitride, SrTaO2N, and its solid solutions. Urea was employed as a solid nitriding agent to eliminate the use of toxic NH3 gas. In addition, utilization of sol-gel-derived Ta2O5 gel as a Ta precursor allowed for completion of nitridation within a shorter period and at a lower calcination temperature compared with the conventional ammonolysis process. Optimization of the reaction conditions, such as the urea content, allowed for the production of solid solutions of SrTaO2N and Sr1.4Ta0.6O2.9. The products exhibited optical absorption and chromatic colors because of the narrower band gaps of Oxynitrides compared with those of oxides. The O/N ratios of the solid solutions were easily adjusted by varying the amount of urea in the mixture of precursors. As a result, the colors of the products ranged from yellow to brown. The nitridation process and products developed in this study are interesting environmentally benign alternatives to conventional inorganic pigments.
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synthesis of perovskite type Oxynitrides srnb o n 3 and cata o n 3 using carbon nitride
Ceramics International, 2020Co-Authors: Qian Yang, Yuji Masubuchi, Mikio HiguchiAbstract:Abstract The synthesis of oxynitride perovskites based on the use of gaseous ammonia as the nitrogen source requires high reaction temperatures and long durations. In the resent work, reduction and nitridation reactions using carbon nitride (C3N4) were employed to prepare SrNbO2N and CaTaO2N from their oxide precursors, without the use of ammonia. The phase evolution behaviors and the reaction mechanisms were investigated by acquiring thermogravimetric and X-ray diffraction data. The formation of metal cyanamide as an intermediate was found to be vital to realizing low-temperature synthesis of these compounds. Scanning electron microscopy observations also indicated that the particle sizes of the Oxynitrides prepared using C3N4 were smaller than those obtained by ammonolysis reactions, due to the low formation temperature of 800 °C associated with the present C3N4 process.
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Remarkable effects of local structure in tantalum and niobium Oxynitrides
Progress in Solid State Chemistry, 2018Co-Authors: Shinichi Kikkawa, Akira Hosono, Yuji MasubuchiAbstract:Abstract Compounds that contain two types of anion are attracting attention as a new field of solid state chemistry. The nitride anion is similar to the oxide anion in size and nature. They coordinate together to cations in Oxynitrides to form characteristic local structures around them in a certain way. Special properties induced by the specific local structure have been observed in Oxynitrides. Ferroelectricity was identified in oxynitride perovskites, especially those of tantalum, because the oxide and nitride anions form a polar ordered local crystal structure around Ta5+ in the 5d0 electron configuration. The critical current density in superconductivity was enhanced by the formation of clusters in niobium Oxynitrides with the rocksalt-type structure. Main group elements doped into the niobium Oxynitrides, especially silicon, are coordinated mainly by oxides with some amount of nitrides to form silicon oxide-like clusters. The niobium in the oxynitride has some 4d electrons to maintain the superconductivity in the niobium oxynitride host. Here, the preparation, crystal structure and properties of Oxynitrides formed with tantalum and niobium are reviewed.
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crystal structure and superconductive characteristics of nb0 89al0 11 Oxynitrides
Journal of Solid State Chemistry, 2010Co-Authors: Y Ohashi, Yuji Masubuchi, Teruki Motohashi, Shinichi KikkawaAbstract:Abstract The crystal structure and superconductive characteristics of the niobium–aluminum Oxynitrides were investigated. Single-phase products were successfully obtained starting from a cation ratio of Nb 0.89 Al 0.11 . The as-nitrided product crystallized in a cation-deficient rock-salt type structure with a chemical formula of (Nb 0.60 Al 0.08 □ 0 .32 )(O 0.21 N 0.79 ), while annealing at 1773 K under a nitrogen pressure of 0.5 MPa led to a highly crystallized product with a simple rock-salt type structure represented as (Nb 0.89 Al 0.11 )(O 0.17 N 0.85 ). Upon post-annealing, both the critical temperature ( T c ) and the superconductive volume fraction ( V SC ) of the oxynitride were significantly enhanced from T c ≈7 K and V SC =23% for the as-nitrided product to T c =17.3 K and V SC =91% for the post-annealed product.
