Sb2O4 at high pressures and high temperatures

Investigations on Sb₂O₄ at high pressure and temperature have been performed up to 600 °C and up to 27.3 GPa. The so-called “high temperature” phase (β-Sb₂O₄) was obtained following pressure increase at ambient temperature and at relatively low temperatures. Thus, in contrast to previous perceptions, β-Sb₂O₄ is the modification more stable at high pressures, i.e., at low temperatures. The fact that the metastable α-form is typically obtained through the conventional way of preparation has to be attributed to kinetic effects. The pressure-induced phase transitions have been monitored by in-situ X-ray diffraction in a diamond anvil cell, and confirmed ex-situ, by X-ray diffraction at ambient conditions, following temperature decrease and decompression in large volume devices. Bulk modulus values have been derived from the pressure-induced volume changes at room temperature, and are 143 GPa for α-Sb₂O₄ and 105 GPa for the β-Sb₂O₄.     

Synthesis and photoluminescence of Eu-doped Y2Sn2O7 nanocrystals

A facile CTAB-assisted sol-gel route has been successfully established to synthesize Y₂Sn₂O₇ nanocrystals with pyrochlore structure. The route involves first the formation of CTAB-inorganics mesostructures as precursors and then their thermal decomposition to yield the final product. Well-crystallized and phase-pure Y₂Sn₂O₇ particles of ∼40 nm in size can be readily obtained at 600°C, a temperature much lower than that of the conventional solid-state method. Furthermore, photoluminescence characterization of the Y₂Sn₂O₇ nanocrystals doped with 5 mol% Eu³⁺ was carried out and the results show that the as-synthesized material display intense and prevailing emission at 589 nm belonging to the magnetic dipole transition.     

Hydrothermal synthesis and structure determination of the new vanadium molybdenum mixed oxide V1.1Mo0.9O5 from synchrotron X-ray powder diffraction data

A new vanadium molybdenum mixed oxide V_1.1Mo_0.9O₅ [V(V)_0.2V(IV)_0.9Mo(VI)_0.9O₅] has been synthesized, as a pure phase, via hydrothermal methods in the presence of molybdic acid and vanadyl sulfate. Its crystal structure has been solved ab initio from high-resolution powder diffraction data collected at the ESRF beamline ID31. This compound crystallizes in the monoclinic symmetry, space group C2/m, with cell dimensions , , , β=90.625(3)° and Z=2 per formula. The structure consists of double strings of VO₅ square pyramids sharing edges and corners along [100] and [010], and more weakly bound along [001]. In this latter direction, the bond (V,Mo)-O=2.377 Å, while remaining long, leads for the first time to the interpenetration of the apical oxygens of the [(V,Mo)₂O₅]_n layers, resulting in a three-dimensional (3D) structure closely related to R-Nb₂O₅. This structure will be compared to the pure layer structure of V₂O₅ where this bond reaches 2.793 Å.     

Synthesis of morphology-controllable mesoporous Co3O4 and CeO2

Recently, extensive works have been devoted to the morphology control of mesoporous materials with respect to their use in various applications. In this paper, we used two kinds of mesoporous silica, SBA-15 rods and spheres as hard templates to synthesize morphology-controllable mesoporous metal oxides. By carefully controlling the loading of metal precursors in the mesopores of the hard template, mesoporous Co₃O₄ and CeO₂ with different morphologies, such as micrometer-sized rod, hollow sphere, saucer-like sphere, and solid sphere were conveniently obtained. The structural properties of these materials were characterized by XRD, BET, SEM and TEM. In addition, it is found that the differences observed in the textural properties of the two mesoporous metal oxides nanocasted from the same template can be attributed to the properties of metal precursors and the interaction between metal oxide and SiO₂. Thus-obtained mesoporous metal oxides with such special morphologies may have a potential application in the field of environmental catalytic oxidation.     

Sb2O3/BiVO4/WO3异质结构建及光电催化合成过氧化氢

采用溶剂热法-旋涂法构建了Sb₂O₃/BiVO₄/WO₃半导体异质结,并采用X射线衍射、扫描电子显微镜、X射线光电子能谱等手段表征了其物化性质。在1.23 V(vs RHE)电位下,BiVO₄/WO₃的光电流密度相对于BiVO₄提高了2倍。进一步复合Sb₂O₃之后,虽然Sb₂O₃/BiVO₄/WO₃薄膜的光电流密度有所下降,但其光电催化产H₂O₂的法拉第效率和产生速率得到明显提升。在1.89V(vs RHE)电位下,3c-Sb₂O₃/BiVO₄/WO₃薄膜产H₂O₂的法拉第效率提高到约19%;1c-Sb₂O     

Polyol-mediated solvothermal synthesis and luminescence properties of CeF3, and CeF3:Tb nanocrystals

CeF₃ and CeF₃:Tb³⁺ nanocrystals were successfully synthesized through a facile and effective polyol-mediated route with ethylene glycol (EG) as solvent. Various experimental techniques including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) spectra as well as decay dynamics were used to characterize the samples. The results indicated that the content of NH₄F and reactant concentrations were key factors in the product shape and size. Excessive NH₄F was necessary for the formation of hexagonal nanoplates. The specific morphology of product can be controlled by changing the NH₄F content and reactant concentrations. In addition, Tb³⁺ doped-CeF₃ sample shows strong green emission centered at 544 nm corresponding to the ⁵D₄-⁷F₅ transition of Tb³⁺. Due to the decrease of nonradiative decay rate, the lifetime of ⁵D₄ level of Tb³⁺ become longer gradually upon increasing the size of product.     

Sb2O3/BiVO4/WO3异质结构建及光电催化合成过氧化氢

采用溶剂热法-旋涂法构建了Sb₂O₃/BiVO₄/WO₃半导体异质结,并采用X射线衍射、扫描电子显微镜、X射线光电子能谱等手段表征了其物化性质。在1.23 V(vs RHE)电位下,BiVO₄/WO₃的光电流密度相对于BiVO₄提高了2倍。进一步复合Sb₂O₃之后,虽然Sb₂O₃/BiVO₄/WO₃薄膜的光电流密度有所下降,但其光电催化产H₂O₂的法拉第效率和产生速率得到明显提升。在1.89V(vs RHE)电位下,3c-Sb₂O₃/BiVO₄/WO₃薄膜产 H₂O₂的法拉第效率提高到约 19%;1c-Sb₂O₃/BiVO₄/WO₃薄膜 H₂O₂产生速率从约2.1 μmol·h^-1·cm^-2提高到约3.6 μmol·h^-1·cm^-2。此外,Sb₂O₃的复合显著提高了BiVO₄/WO₃电极材料的光电催化稳定性。     

Hydrothermal Synthesis and Characterization of (H3N(CH2)4NH3)[V6O14]

A new layered vanadium oxide [H₃N(CH₂)₄NH₃](V₆O₁₄) was synthesized hydrothermally under autogenous pressure at 180°C for 48 h from a mixture of H₂N(CH₂)₄NH₂ and V₂O₅ in aqueous solution. Its structure was determined from single-crystal X-ray diffraction at room temperature with final R=0.0774 and R_w=0.0893. It crystallizes in the monoclinic system (space group P2₁/n with a=9.74(2) Å, b=6.776(5) Å, c=12.60(2) Å, β=96.1(1)°, V=827(2) ų and Z=2). This compound contains mixed-valence V⁵⁺/V⁴⁺ vanadium oxide layers built from [V^VO₄] tetrahedra and pairs of edge-sharing [V^IVO₅] square pyramids with protonated organic amines occupying the interlayer space.     

A novel nonaqueous route to V2O3 and Nb2O5 nanocrystals

The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V₂O₃ and Nb₂O₅. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V₂O₃ crystals exhibit particle sizes between 20 and 50 nm, and the Nb₂O₅ crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character.     

Hydrothermal homogeneous urea precipitation of hexagonal YBO3:Eu nanocrystals with improved luminescent properties

Well-crystallized YBO₃:Eu³⁺ nanocrystals were prepared by a mild hydrothermal method in the presence of urea, and a pure hexagonal phase could be obtained at a low temperature of 200°C only. The photoluminescence spectra showed a remarkable improvement on the chromaticity as well as the luminescent intensity, compared with the samples synthesized by solid-state reaction (SR). The effects of the synthesis temperature, urea concentration, and the doping concentration of Eu³⁺ on the crystallization and luminescent properties were investigated. The results showed that both high temperature and low urea concentration were favorable to the formation of YBO₃:Eu³⁺, and the ratio of red emission (⁵D₀→⁷F₂) to orange emission (⁵D₀→⁷F₁) increased with decreasing the synthesis temperature and the urea concentration. Furthermore, the samples exhibited a higher quenching concentration of Eu³⁺ in comparison with those prepared by the SR, which was beneficial to further enhancing the luminescent intensity. These synthesis-dependent phenomena were analyzed, and possible explanations were proposed.     

Raman, XRD and microscopic investigations on CeO2-Lu2O3 and CeO2-Sc2O3 systems: A sub-solidus phase evolution study

A sub-solidus phase evolution study was done in CeO₂-Sc₂O₃ and CeO₂-Lu₂O₃ systems under slow-cooled conditions from 1400 °C. Long-range order probing of X-ray diffraction technique is utilized in conjunction with the ability of Raman spectroscopy to detect the changes in local co-ordination. Lu₂O₃ showed solubility of 30 mol% in CeO₂, thus forming an anion deficient fluorite-type (F-type) solid solution, whereas Sc₂O₃ did not show any discernible solubility. A biphasic region (F+C) was unequivocally detected by Raman spectroscopy in Ce_1−xLu_xO_2−x/2 (0.4?x?0.9) and in Ce_1−xSc_xO_2−x/2 (0.1?x?0.9) systems. Raman spectroscopy was valuable in studying these systems since oxygen vacancies are created on doping RE₂O₃ into ceria and Raman spectroscopy is very much sensitive to oxygen polarizability and local coordination. Back scattered images collected on representative compositions support the above-mentioned results.     

Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co₃O₄with MgO (0.4–6 mol%) and V₂O₅ (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H₂O₂ at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V₂O₅ doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co₃O₄ solid. Treatment of Co₃O₄ with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H₂O₂ decomposition, of Co₃O₄ was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant (k) measured at 40°C on Co₃O₄ due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V₂O₅-doping of Co₃O₄ brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V₂O₅-doped Co₃O₄ solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO³⁺–CO²⁺ ion pairs and created Mg²⁺–CO³⁺ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H₂O₂. V₂O₅-doping exerted an opposite effect via decreasing the number of CO³⁺–CO²⁺ ion pairs besides the possible formation of cobalt vanadate.     

Complex thermal evolution of V2O5 and MoO3 cell parameters in the range

Cell parameter evolution versus temperature has been established for both V₂O₅ and MoO₃, from 15 to 953 and 893 K, respectively. Both oxides preserve their orthorhombic crystal system and their respective space groups Pmmn and Pnma in the whole temperature range. Unusual evolution of the unit cells have been detected in these oxides and proposals are made to follow them based on detailed structural analysis. Three temperature domains have been evidenced for V₂O₅ marked by breaks at RT and 800 K; for MoO₃, only two domains are defined below and above 400 K. For each domain the quality of cell parameters and X-ray powder pattern indexing, have been checked by mathematical functions to buttress their coherent evolution within each temperature domain.     

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb₂Sb₂O₆(O,OH). The mineral is characterised by an intense Raman band at 656 cm⁻¹ assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm⁻¹ are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm⁻¹ are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm⁻¹ may be assigned to δOH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm⁻¹ are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm⁻¹ supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb₂Sb₂O₆(O,OH,H₂O).     

水热法制备Sb2S3纳米棒有序阵列

以Sb(S₂CNEt₂)₃为单源前驱体，通过改变时间、温度、表面活性剂等反应条件，用水热法成功合成了各种尺寸的Sb₂S₃纳米棒及其有序阵列。X-射线衍射(XRD)、能量分散光谱(EDS)以及选区电子衍射(SAED)研究表明纳米棒由正交晶系Sb₂S₃单晶构成。扫描电子显微镜(SEM)和透射电子显微镜(TEM)研究显示Sb₂S     

Enhanced photocatalytic activity of Eu2O3/Ta2O5 mixed oxides on degradation of rhodamine B and 4-nitrophenol

Europium oxide/tantalum pentoxide (Eu₂O₃/Ta₂O₅) mixed oxides with different Eu₂O₃ dopings were prepared by a single-step sol–gel process via hydrolysis of tantalum pentachloride in the presence of europium nitrate. The products were in the amorphous and orthorhombic phase structures, respectively, based on the different calcination temperatures (200 and 500 °C). Composition, morphology, phase structure, Eu₂O₃-doping mode in the Ta₂O₅ matrix and optical absorption property of the products were characterized by inductively coupled plasma atomic emission spectroscopy (ICP-AES), field emission scanning electron microscopy (FESEM), X-ray diffraction patterns (XRD), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectroscopy (UV–vis/DRS). The UV-light photocatalytic activity of the products was evaluated by degradation of aqueous rhodamine B (RB) and 4-nitrophenol (4-NP). The results showed that the photocatalytic activity of as-prepared Eu₂O₃/Ta₂O₅ was higher than that of pure Ta₂O₅ regardless of their phase structures. Among the tested samples, Eu₂O₃/Ta₂O₅ with 0.49% Eu loading obtained with 200 °C exhibited the highest activity to degradation of the above two model molecules. The reasons of this enhanced photocatalytic activity were discussed.     

Formation of [Cp2TiSbMe2]2, [Cp2TiSb(SiMe3)2]2 and [Cp2TiCl]2·2Mes4Sb2

Reactions of [Cp₂Ti(btmsa)] (btmsa = bis(trimethylsilyl)acetylene) with R₄Sb₂ (R = Me, Me₃Si) give [Cp₂TiSbMe₂]₂ (1) or [Cp₂TiSb(SiMe₃)₂]₂ (2) respectively. [Cp₂TiCl]₂·2Mes₄Sb₂ (3) is serendipitously formed from [Cp₂Ti(btmsa)] and Mes₂SbH containing NH₄Cl traces.     

Low temperature synthesis of Mn3O4 polyhedral nanocrystals and magnetic study

Manganese oxide (hausmannite) polyhedral nanocrystals were prepared by a microwave-assisted solution-based method using Mn(CH₃COO)₂ and (CH₂)₆N₄ at 80 °C. The as-prepared Mn₃O₄ nanocrystals were characterized by means of X-ray diffraction, field-emission transmission electron microscopy, field-emission scanning electron microscopy and Raman spectrum. Mn₃O₄ polyhedral nanocrystals prepared by microwave heating at 80 °C for 60 min were of cubic and rhombohedral shapes with the edge lengths in the range of 15-40 nm. Mn₃O₄ nanocrystals grew following the Ostwald ripening mechanism with increasing reaction time. High-resolution transmission electron microscopy and selected area electron diffraction confirm that the as-obtained polyhedral nanocrystals were single-crystalline. The magnetic behavior of Mn₃O₄ nanocrystals was studied. Mn₃O₄ nanocrystals show an obvious ferromagnetic behavior at low temperatures. The magnetic behavior of Mn₃O₄ nanocrystals was sensitive to crystal size. Ferromagnetic onset temperatures (T_c) of samples 1 and 3 are 40.6 and 41.1 K, respectively, lower than that observed for bulk Mn₃O₄ (42 K).     

Cristallisation de LiFe5O8 dans un verre 0,9 Li2B2O4 - 0,1 LiFe5O8

X-Ray diffraction, transmission electron microscopy, and magnetic measurements are used to study the crystallization of an amorphous compound: Li₂B₂O₄ (90 mole%)-LiFe₅O₈ (10 mole%). The crystalline phase which first appears in the amorphous matrix is LiFe₅O₈. The average particle size (50 to 300 Å) may be controlled by varying the temperature of annealing and/or the time of annealing. The crystallization kinetics are similar to those of metallic glasses. The fraction transformed, x, as a function of time, satisfies the Johnson-Mehl-Avrami equation with an exponent n of 0.75. The activation energy for the crystallization process is approximately 0.6 eV. Both these values characterize a primary crystallization.     

Sr4PbPt4O11, the first platinum oxide containing Pt2 ions

We report the synthesis and crystal structure of the new compound Sr₄PbPt₄O₁₁, containing platinum in highly unusual square pyramidal coordination. The crystals were obtained in molten lead oxide. The structure was solved by X-ray single crystal diffraction techniques on a twinned sample, the final R factors are R=0.0260 and wR=0.0262. The symmetry is triclinic, space group P1¯, with , , , α=90.421(3)°, β=89.773(8)°, γ=90.140(9)° and Z=2. The structure is built from dumbell-shaped Pt₂O₉ entities formed by a dinuclear metal-metal bonded Pt₂⁶⁺ ion with asymmetric environments of the two Pt atoms, classical PtO₄ square plane and unusual PtO₅ square pyramid. Successive Pt₂O₉ entities deduced from 90° rotations are connected through the oxygens of the PtO₄ basal squares to form [Pt₄O₁₀⁸⁻]_∞ columns further connected through Pb²⁺ and Sr²⁺ ions. Raman spectroscopy confirmed the peculiar platinum coordination environment.