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Vacancy-Driven Robust Metallicity of Structurally Pinned Monoclinic Epitaxial VO <sub/>2</sub> Thin Films
摘要： Vanadium dioxide (VO2) is a strongly-correlated material with 3d-electrons, which exhibits temperature-driven insulator-to-metal transition with a concurrent change in the crystal symmetry. Interestingly, even modest changes in stoichiometry-induced orbital occupancy dramatically affect the electrical conductivity of the system. Here, we report a successful transformation of epitaxial monoclinic VO2 thin films from a conventionally insulating to permanently metallic behavior by manipulating the electron-correlations. These ultrathin (~10 nm) epitaxial VO2 films were grown on NiO (111)/Al2O3 (0001) pseudomorphically, where the large misfit between NiO and Al2O3 were fully relaxed by domain matching epitaxy. Complete conversion from an insulator to permanent metallic phase is achieved through injecting oxygen vacancies (x~0.20±0.02) into the VO2-x system via annealing under high vacuum (~5x10-7 Torr) and elevated temperature (450 oC). Systematic introduction of oxygen vacancies partially converts V4+ to V3+ and generates unpaired electron charges which result in the emergence of donor states near Fermi level. Through the detailed study of the vibrational modes by Raman spectroscopy, hardening of the V-V vibrational modes and stabilization of V-V dimers are observed in vacuum-annealed VO2 films providing conclusive evidence for stabilization of monoclinic phase. This ultimately leads to convenient free-electron transport through the oxygen-deficient VO2-x thin films resulting in the metallic character at room temperature. With these results, we propose a defect engineering driven pathway through the control of oxygen vacancies to tune electrical and optical properties in epitaxial monoclinic VO2.
关键词： Defect engineering,Oxygen Vacancy,Metallicity,Mott transition,Metallic monoclinic VO2,Charge doping
更新于2025-09-23 15:23:52
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[IEEE 2018 14th International Conference on Advanced Trends in Radioelecrtronics, Telecommunications and Computer Engineering (TCSET) - Lviv-Slavske, Ukraine (2018.2.20-2018.2.24)] 2018 14th International Conference on Advanced Trends in Radioelecrtronics, Telecommunications and Computer Engineering (TCSET) - New high-efficiency material for acoustooptic modulators. Anisotropy of piezooptic effect in TGS crystals
摘要： The photoelastic characteristics of high-efficiency acoustooptic materials of triglycine sulfate monoclinic syngony were investigated. The anisotropy of the piezooptic coefficients of triglycine sulfate crystals was studied by the method of general and indicative surfaces. The piezooptic interaction geometry characterized by the maximum value of the acoustooptic figure-of-merit of this crystal is in order higher than the same value in other crystals used in the IR acoustooptic devices.
关键词： anisotropy,monoclinic syngony,acoustooptic efficiency,piezooptic coefficients,triglycine sulfate,piezooptic effect
更新于2025-09-23 15:22:29
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Multifunctional monoclinic VO2 nanorod thin films for enhanced energy applications: Photoelectrochemical water splitting and supercapacitor
摘要： Monoclinic VO2 nanorod thin films were deposited on indium?tin-oxide-coated glass substrates using radio-frequency reactive magnetron sputtering at a substrate temperature of 300 °C and various O2 flow rates. The thin films were characterized via standard analysis techniques. The VO2 thin films exhibited a highly crystalline monoclinic phase with an indirect band gap of ~1.73 eV. At optimized O2 flow rate (4 sccm), the thin films was observed nanorod structures, exhibited a remarkable photocurrent of ~0.08 mA cm?2 during photoelectrochemical water splitting in the visible region. Electrochemical performance tests of the nanorod films revealed a specific capacitance of ~486 mF cm?2 at a scan rate of 10 mVs?1. In addition, amperometric I–t curves showed that VO2 thin film electrodes were highly stable during the photo-oxidation process. The nanorod films also exhibited a good specific capacitance of ~120 mF cm?2 after 5000 cycles at a scan rate of 100 mVs?1. The photocurrents during photoelectrochemical water splitting and the specific capacitance of VO2 thin films deposited at O2 flow rates of 2 and 6 sccm were 0.06 and 0.07 mA cm?2 and 398 and 37 mF cm?2, respectively. The films deposited under Ar at 8 sccm and O2 at 4 sccm showed the highest photoelectrochemical water splitting performance and specific capacitance, owing mainly to their nanorod-like morphology.
关键词： Supercapacitor,Partial pressure,Reactive sputtering,Photoelectrochemical water splitting,VO2,Monoclinic
更新于2025-09-23 15:22:29
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Dye Mixtures Degradation by Multi-Phase BiVO<sub>4</sub> Photocatalyst
摘要： The objective of this research was to prepare multi–phase bismuth vanadate (BiVO4) powder using the solvothermal method to be used as a photocatalyst. In the preparation step, bismuth nitrate and ammonium vanadate were used as the precursors with a mole ratio of 1:1. The mixed solution was diluted to 0.025 M with acetic acid and heated at 200 oC for 2 h in a Teflon–lined stainless steel autoclave vessel. Multi–phase BiVO4 was obtained without calcination step. Multi–phase BiVO4 was characterized by X–ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR), and energy dispersive spectroscopy (EDS). The efficiency of multi–phase BiVO4 for photocatalytic degradation of the mixed dye of methylene blue (MB) and rhodamine B (RhB) solution under UV light irradiation was studied. The concentration of the mixed dye solution was measured by UV–Vis spectrophotometry (UV–Vis). The effect of concentration of catalyst and pH of solution was studied. The optimum conditions for photocatalytic degradation of mixed dye solution were obtained at 0.8 g/L for concentration of multi–phase BiVO4 and 7.78 for initial pH of the mixed dye solution.
关键词： BiVO4,Photocatalytic,Tetragonal,Monoclinic,Solvothermal
更新于2025-09-23 15:22:29
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European Microscopy Congress 2016: Proceedings || Structure solution of the complex λ-La6W2O15
摘要： The structure solution of the complex β-Ga2O3 (β-Ga2O3) phase has been studied by a number of groups [1-3], but little detailed information has been reported due to the lack of good single crystals. The β-Ga2O3 phase has a monoclinic structure with space group C2/m and lattice parameters a = 12.23 ?, b = 3.04 ?, c = 5.80 ?, β = 103.7°. Recently, the structures of La2Ga2O7, La1.8Sr0.2Ga2O6.9 and La0.9Sr0.1Ga0.9Mg0.1O2.9 have been solved using X-ray powder diffraction (XRPD) [4-7]. The β-Ga2O3 phase has been studied by a number of groups [8-11], but little detailed information has been reported due to the lack of good single crystals. The β-Ga2O3 phase has a monoclinic structure with space group C2/m and lattice parameters a = 12.23 ?, b = 3.04 ?, c = 5.80 ?, β = 103.7°. Recently, the structures of La2Ga2O7, La1.8Sr0.2Ga2O6.9 and La0.9Sr0.1Ga0.9Mg0.1O2.9 have been solved using X-ray powder diffraction (XRPD) [4-7].
关键词： structure solution,β-Ga2O3,X-ray powder diffraction,monoclinic,lattice parameters
更新于2025-09-23 15:22:29
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Gram scale synthesis of monoclinic VO2 microcrystals by hydrothermal and argon annealing treatment
摘要： We report gram scale synthesis of 100 % phase fraction of VO2 (M) monoclinic in powder form with reversible phase transition by combining hydrothermal method and Ar annealing at high temperature. Optimization of single phase VO2 (M) growth and its phase transition characteristics have been analysed systematically by varying growth parameters such as time, synthesis temperature and post growth annealing conditions. Argon annealing of hydrothermally grown VO2 powders at 800°C found to play key role in obtaining VO2 (M) phase in gram scale with characteristic phase transition temperature of 68°C. In-situ TEM has been performed to investigate the microstructure and phase change across the annealing temperature. Detailed characterizations have been carried out to correlate the phases, microstructure and transition temperature of VO2 with respect to growth parameters.
关键词： metal-insulator transition,annealing treatment,monoclinic VO2,in-situ TEM,microcrystals,Scalable synthesis
更新于2025-09-23 15:21:21
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Luminescence of monoclinic Y2O3:Eu nanophosphor produced via laser vaporization
摘要： Europium doped Y2O3spherical nanoparticles with the diameter ~10 nmobtained via cw laser vaporization are shown to crystallize in monoclinic symmetry class (C2/m space group). The size of nanoparticles established via HRTEM coincides with coherent scattering region established by XRD. Luminescence spectrum in the vicinity of ultranarrow transition demonstrates three peaks consistent with three inequivalent positions of Eu3t ion in monoclinic Y2O3 lattice. Hypersensitive transition dominates in the spectrum, admitting the lack of inversion symmetry at Cs sites occupied by Eu3t. The spectrum of hypersensitive transition is expanded to the red part of spectrum due intense transitions terminating at higher-lying components of crystal-field-split 7F2 energy level. Obtaining chromaticity coordinates (0.669, 0.331)and absolute quantum yield (~21%) is possible using red phosphor based on monoclinic Y2O3:Eu3t.
关键词： Laser vaporization,Monoclinic Y2O3:Eu nanophosphor,Photoluminescence of Eu3t
更新于2025-09-23 15:21:01
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Determination of 60° polarization nanodomains in a relaxor-based ferroelectric single crystal
摘要： Here, we report a determination of monoclinic nanodomains in PMN-xPT with x ? 31%PT by using scanning convergent beam electron diffraction (SCBED). We show the presence of 60 6 a degree nanodomains with Cm-like symmetry as well as signi?cant variations (a) in local polarization directions across lengths of (cid:3)10 nm. The principle of our technique is general and can be applied for the determination of polarization domains in other ferroelectric materials of different symmetry. VC 2015 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4932955]
关键词： ferroelectric materials,scanning convergent beam electron diffraction,monoclinic nanodomains,PMN-xPT,SCBED
更新于2025-09-23 15:21:01
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Spectroscopy, Crystal and Molecular Structures of New 4-Acylpyrazolone Dinitrophenylhydrazones
摘要： Still looking at the development of new materials with unique properties and taking advantage of the nucleophilic properties of amines to form stable azomethines, dinitrophenylhydrazine was reacted with 4-ethyl-5-methyl-2-phenyl-pyrazol-3-one and then with 4-propyl-5-methyl-2-phenyl-pyrazol-3-one to get and respectively, 4-propyl-5-methyl-2-phenyl-pyrazol-3-one dinitrophenylhydrazone (Pmpp-Dh), via a simple condensation reaction in a one-pot synthesis system. Careful interpretations of results from elemental analysis, mass and NMR spectroscopy were in agreement with single-crystal X-ray diffraction data. Reported Schiff bases in their single-crystal solid state exist in imine keto tautomer form, each crystallizing in a monoclinic crystal system, with a space group of C2/c (No. 15) in Empp-Dh and P21/c (No. 14) in Pmpp-Dh. They have extensive intra- and inter-molecular hydrogen as well as C–H···π-ring interactions.
关键词： Schiff base,monoclinic,spectroscopy,dinitrophenylhydrazone,chemical shift,acylpyrazolone,single crystal
更新于2025-09-23 15:21:01
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Synthesis of high-purity zircon, zirconia, and silica nanopowders from local zircon sand
摘要： High-purity zircon (ZrSiO4) nanopowder was successfully produced from Indonesian natural zircon sand using a low-cost purification approach via magnetic separation, immersion in HCl, and reaction with NaOH, followed by a top-down nanosizing process using wet ball-milling for 10 hours and annealing at 200 °C for 2 hours. Furthermore, polymorph zirconia (ZrO2 – amorphous, tetragonal, and monoclinic) and silica (SiO2 – amorphous and cristobalite) nanopowders were also successfully derived from the purified zircon powder using a bottom-up method via alkali fusion and co-precipitation processes followed by calcination. The crystallite size of the powders was estimated from X-ray diffraction (XRD) data analysis to give 40, 31, 61, and 149 nm, respectively, for the zircon, tetragonal- and monoclinic-zirconia, and cristobalite. Microstructural characteristics of the zircon, silica, and zirconia nanopowders were revealed in transmission electron microscopy (TEM) images which confirmed that the average sizes of the particles were in a good agreement with the XRD estimated values.
关键词： zircon,tetragonal zirconia,amorphous silica,nanopowder,cristobalite,monoclinic zirconia
更新于2025-09-23 15:19:57