Ordered arrays of high-quality single-crystalline α-Si3N4 nanowires: Synthesis,properties and applications

Ordered arrays of high-quality single-crystalline α-Si₃N₄ nanowires (NWs) have been synthesized via thermal evaporation and detailed characteristics of the NWs have been analyzed by employing scanning electron microscope (SEM) along with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscope (HRTEM), X-ray diffraction (XRD), X-ray photospectroscopy (XPS), infrared (IR), photoluminescence (PL) and in situ I–V measurements by STM/TEM holder. The microscopic results revealed that the NWs having diameter in the range of ~30–100 nm and length in microns. Furthermore, the NWs are found to be single crystalline grown along [0 0 1] direction. The elemental composition and valence states of elements are analyzed by EDS and XPS. The room temperature PL spectra exhibit a broad range visible emission band. The electron transport property of a single NW illustrates the symmetric I–V curve of a semiconductor. The possible growth mechanism is also briefly discussed.     

Surface kinetics of nitrogen dissolution and its correlation to the slag structure in the CaO―SiO2, CaO―Al2O3, and CaO―SiO2―Al2O3 slag system

The kinetics of nitrogen dissolution into molten slag at 1873 K was investigated by an isotope exchange technique. Rate constants were correlated with the molten slag structure obtained from FT-IR spectra. The rate constant in the CaO―SiO₂ binary system showed a maximum value at a specific slag composition followed by a decrease in the rate due to excess O²⁻ blocking the surface sites for nitrogen adsorption. The rate constant in the CaO―Al₂O₃ binary system was comparatively constant within the experimental range of 45 mass% to 60 mass%. The rate constant in the CaO―SiO₂―Al₂O₃ ternary slag system was measured within the boundary of the liquidus line and showed a close correlation with the slag structure. Furthermore, the rate constant in the CaO―SiO₂―Al₂O₃ ternary system was found to be significantly higher compared to the binary system due to the correlated effect of lower binding energies of the Al―O bonds and the increased number of reaction sites available when smaller Si―O tetrahedral were simultaneously present with Al―O bonds.     

Investigation of recombination and trapping processes in 3As2Se32Sb2Se3 amorphous films by photoconductivity method

Photoconductivity experiment has been performed on high resistivity ($\text{π ? 10}{}^9\text{Ω-}\text{cm}$) 3As₂Se₃2Sb₂Se₃ amorphous films in the temperature range from 278°K to 308°K, as a function of light intensity, I₀. The results are that at intermediate light levels the photocurrent varies as I₀^0.7 and at high light levels the photocurrent is directly proportional to I₀. A simple recombination and trapping model is developed to interpret the observed photoconductivity data. From the temperature dependence of the photocurrent, an effective trap level located 0.3 eV below the band edge is deduced.     

Synthesis and X-ray structural investigation of (C3N6H7)4(CN3H6)2[UO2(CrO4)4] · 4H2O and (H3O)6[UO2(CrO4)4]

Single crystals of the compounds (C₃N₆ H₇)₄(CN₃H₆)₂[UO₂(CrO₄)₄] · 4H₂O (I) and (H₃O)₆[UO₂(CrO₄)₄] (II) are synthesized, and their structures are investigated using X-ray diffraction. Compound I crystallizes in the triclinic system with the unit cell parameters a = 6.3951(8) ?, b = 10.8187(16) ?, c = 16.9709(18) ?, α = 93.674(4)°, β = 97.127(4)°, γ = 92.020(4)°, space group, P Z = 1, V = 1161.6(3) ?³, and R = 0.0470. Crystals of compound II belong to the monoclinic system with the unit cell parameters a = 14.3158(4) ?, b = 11.7477(3) ?, c = 13.1351(4) ?, β= 105.836(1)°, space group C2/c, Z = 4, V = 2125.2(1) ?³, and R = 0.0213. The uranium-containing structural units of crystals I and II are mononuclear anionic complexes of the composition [UO₂(CrO₄)₄]⁶⁻ with an island structure, which belong to the crystal-chemical group Am ₁⁴ (A = UO₂₊², M ¹ = CrO₂₋⁴) of the uranyl complexes. The [UO₂(CrO₄)₄]⁶⁻ anionic complexes are joined into a three-dimensional framework through the electrostatic interactions with outer-sphere cations and a system of hydrogen bonds. Original Russian Text ? L.B. Serezhkina, E.V. Peresypkina, A.V. Virovets, A.G. Verevkin, D.V. Pushkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 2, pp. 284–290.     

Synthesis and Structural Characterization of Two New Layered Inorganic–Organic Hybrid Zinc Phosphites Templated by Cyclam: Zn(HPO3)2·0.5(C10H28N4) and Zn2(HPO3)3·0.5(C10H28N4)

Abstract  

Using 1,4,8,11-tetraazacyclotetradecane (cyclam) as a template, two new layered zincophosphites, Zn(HPO₃)₂·0.5(C₁₀H₂₈N₄) (1) and Zn₂(HPO₃)₃·0.5(C₁₀H₂₈N₄) (2), were synthesized and characterized by single crystal X-ray diffraction. The two new compounds crystallize in the triclinic system with the space group P − 1 and the cell parameters: a = 8.3130 ?, b = 8.7289 ?, c = 9.0055 ?, α = 106.90(1), β = 95.56(1), γ = 105.30(1), V = 592.31 ?³, Z = 2 for 1 and a = 9.0406 ?, b = 9.4234 ?, c = 9.4519 ?, α = 91.19(1), β = 100.73(1), γ = 106.85(1), V = 754.82 ?³, Z = 2 for 2. Both structures are described in terms of phosphometallic slabs hosting the cyclam cation.     

Glass formation and structure of Na2SSiO2 and Na2SB2O3 glasses

Glass-forming regions of the systems Na₂SSiO₂ and Na₂SB₂O₃ have been investigated in order to clarify whether Na₂S could be substituted for Na₂O in sodium silicate or borate glasses, and the results were interpreted in terms of the structures of silicate and borate glasses. No difference was found in the glass-forming range of SiO₂ content between the Na₂SSiO₂ and Na₂OSiO₂ systems, and the red color of Na₂SSiO₂ glasses suggests that the formation of polysulfides in the glass structure is probably due to the entrance of sulfur ions in the non-bridging sites of the glass network. On the other hand, not all of the sulfur added to the glass batches could be retained in the Na₂SB₂O₃ glasses and the amount remaining in the glass products changed depending upon the amount of sodium ions in the glasses. Only a trace of sulfur was observed in the glasses containing less than 13 mol% of Na₂S in the batches, but the sulfur content in the glasses increased steeply with sodium content up to 35 mol%, reached the maximum and then decreased slowly with sodium content. The insolubility of sulfur in the glasses with low sodium content was interpreted based on the compositional dependence of basicity of alkali-borate glasses, and the change in solubility of sulfur with sodium concentration was explained based on the well-known boron anomaly caused by the change in the coordination state of boron and on the formation of non-bridging oxygens or sulfurs in the glass structure.     

Synthesis,morphology and phase transition of the zinc molybdates ZnMoO4·0.8H2O/α-ZnMoO4/ZnMoO4 by hydrothermal method

ZnMoO₄ with a rhombus sheet or flower-like structure, α-ZnMoO₄ and needle-like ZnMoO₄·0.8 H₂O were successfully synthesized by simple hydrothermal crystallization processes with citric acid. ZnMoO₄·0.8 H₂O was easily synthesized in a shorter reaction time (2 h) at a higher reactant concentration. It gradually transformed into ZnMoO₄ with a monoclinic wolframite tungstate structure with an increased reaction time, and pure ZnMoO₄ was obtained with a longer reaction time (8 h). Citric acid (CA) played an important role in controlling the morphology of the as-obtained molybdates. The α-ZnMoO₄ and ZnMoO₄ were synthesized by heating ZnMoO₄·0.8 H₂O at 130 °C for 4 h and 8 h, respectively, under hydrothermal conditions. With transforming of ZnMoO₄·0.8 H₂O to α-ZnMoO₄ and further to ZnMoO₄, the needle-like crystals gradually disappeared and were transformed into crystals with rhombus sheet morphology and then further to pentacle or flower-like crystals that can be ascribed to continuous splitting and growing of the rhombus sheets.     

Eu3+掺杂ZnAl2O4/SiO2微晶玻璃制备与发光性能

采用溶胶-凝胶法制备Eu3+掺杂的Zn Al2O4/Si O2(ZAS)块状透明微晶玻璃发光材料。利用X射线衍射(XRD),透射电子显微镜(TEM)和荧光光谱(PL)等测试手段,系统研究了不同Eu3+掺杂浓度对ZAS发光性能的影响以及不同热处理温度对ZAS∶Eu3+发光性能的影响。结果表明,ZAS∶Eu3+在611 nm处具有强烈的红光发射峰,发射强度随着Eu3+掺杂浓度的增加,出现浓度淬灭效应,当掺杂量为20mol%时,发光强度最大;随着热处理温度的升高,存在高温淬灭效应,当热处理温度为900℃时,材料发光强度最优。CIE色度图分析表明,ZAS∶0.20Eu3+是一种潜在、优良的红光显示微晶玻璃材料。     

Crystallization and phase-separation of Li2OSiO2 glass

The crystallization and phase-separation phenomena in the Li₂OSiO₂ glass are studied by positron lifetime and annihilation lineshape measurements. Analysis of the kinetic data shows three-dimensional morphology of growing crystals. Phase-separation is seen to increase the density of crystal nuclei and the rate of volume crystallization, but it does not affect the morphology. In addition, surface crystallization is detected in glasses with small degrees of phase-separation. The results are consistent with scanning electron and optical micrographs.     

Structure, thermal, and infrared analyses of [NH3(CH2)3NH3]2[Ni(HP2O7)2(H2O)2] ? 4H2O

[NH₃(CH₂)₃NH₃]₂[Ni(HP₂O₇)₂(H₂O)₂] 4H₂O (NiDAP) is a new diphosphate of transition metallic and organic cations obtained from a mixture of H₄P₂O₇, 2NiCO₃ Ni(OH)₂ 4H₂O and NH₂(CH₂)₃NH₂ in a 1:1/6:1 molar ratio. This mixed organo-mineral compound crystallizes in the triclinic system, P¯, with the unit cell dimensions: a = 7.3678(3)~Å, b = 7.8018(5)Å, c = 11.1958(7)Å, = 76.914(4), = 81.052(4), = 85.46(1), V = 618.57(6)ų and Z = 1. The crystal structure of NiDAP consists of a complex anion, [Ni(HP₂O₇)₂(H₂O)₂]^4– and a diammoniumpropane cation. The complex anion is built up from two neutral water molecules (OW1) and two diphosphosphoric anions coordinated to Ni(II) in a bidentate chelating manner. (OW1) molecules link anionic complexes, [Ni(HP₂O₇)₂(H₂O)₂]^4– to create a thick bidimensional layers parallel to the (a, b) plane. These layers are interconnected in three dimensions through hydrogen bonds established between organic cations, the remaining water molecules OW2, OW3, and some external oxygen atoms of the anionic complex arrays. NiDAP was also characterized by IR spectroscopy, TG-DTA, and DSC analyses.     

Brillouin scattering measurements of attenuation and velocity of hypersounds in SiO2B2O3 glasses

Measurements of hypersound wave velocity and attenuation (20–30 GHz) were made at room temperature by Brillouin scattering in SiO₂O₂O₃ glasses. The attenuation shows a maximum with composition. An explanation of this maximum is given in relation to the glass structure. It is thought that this maximum may be due to a coupling effect of hypersounds with structural relaxational process involving SiSi and SiOB bonds.     

Gain cross-section of 1.06 μm emission in Nd-doped SiO2-LaF3 glass-ceramics prepared by sol-gel method

The room temperature near-infrared emission at 1.06 μm corresponding to the ⁴F_3/2 → ⁴I_11/2 laser transition in Nd³⁺-doped SiO₂-LaF₃ transparent glass-ceramics prepared by sol-gel method has been characterized in terms of the product of emission cross-section and fluorescence lifetime. Stimulated emission cross-sections have been calculated from experimental emission spectra using the Füchtbauer-Ladenburg equation. The precipitation of LaF₃ nanocrystals after heat-treatment, confirmed by X-ray diffraction, induces a significant increment of the 1.06 μm near-infrared emission compared with the as made sample. An enhancement of emission cross-section of about 10% has been achieved with increasing temperature of heat-treatment of the nano-ceramming process from 800 to 1000 °C, which is related to the growth of LaF₃ nanocrystals.     

Crystallization of Li2OSiO2 glass studied by positron annihilation

The crystallization of 34 Li₂O65 SiO₂1 P₂O₅ glass has been studied by positron annihilation. The changes in the positron lifetime spectra have been correlated to the magnitude of the amorphous X-ray scattering. A linear relationship has been found for heat-treatment temperatures less than 700°C, above which non-linear phenomena in the lifetime spectra set in. The volume crystallinity reaches a saturation value, which varies from 70% at the heat-treatment temperature of 535°C to 80% at 700°C because of the phase separation. The dimensionality of the crystal growth in this glass is found to be n = 1.5 ± 0.1. The effect of the phase separation on the rate and dimensionality of the crystallization is discussed. The results show that positron annihilation is a sensitive and accurate method to follow crystallization in vitreous materials.     

Invar effect in n-Nb2O5, αht-Nb2O5, and L-Nb2O5

An X-ray diffraction analysis of two commercial sets of niobium pentaoxide (Nb₂O₅) of Nbo-Pt grade has been performed. Each set reveals the coexistence of three modifications: n-Nb₂O₅, α_ht-Nb₂O₅, and L-Nb₂O₅. Anomalous behavior in the structural characteristics, with the occurrence of plateaus upon heating (the invar effect), is established for each phase. It is suggested that the coincidence of the temperature ranges with constant unit-cell parameters in Nb₂O₅ and complex Nb-containing oxides indicates the unified nature of the invar effect, which is related to the defect state of objects under study. Original Russian Text ? L.A. Reznichenko, V.V. Akhnazarova, L.A. Shilkina, O.N. Razumovskaya, S.I. Dudkina, 2009, published in Kristallografiya, 2009, Vol. 54, No. 3, pp. 517–526.     

A neutron small angle scattering study of SiO2Na2 O glasses

The first results obtained by small-angle neutron scattering (SANS) study of sub-liquidus immiscibility of glasses are presented. Measurements were performed on the neutron small-angle scattering spectrometer of the Institut Laue-Langevin (Grenoble, France). The glass studied was 0.88 (SiO₂), 0.12 (Na₂O) from SiO₂Na₂O system which presents a well-known miscibility gap already explored by small-angle X-ray scattering (SAXS) method. Absolute values of the neutron scattering cross section as a function of scattering vector were obtained for this glass quenched and heat treated at 560°C for various lengths of time. It is shown that the ANS method can be used to follow phase separation kinetics and the comparison with SAXS results can in principle be used to separate the effects of density and concentration fluctuations in this system.     

EPR study of crystalline and vitreous forms of the Li2OAl2O3SiO2 system

The epr spectra of V⁴⁺ and radiation centres have been studied in β-eucryptite (LiAlSiO₄), β-, γ-spodumene (LiAlSi₂O₆) and in glasses prepared by the fusion of the single crystals. It is shown that the electronic structures of the vitreous state in the Li₂OAl₂O₃SiO₂ system and that of the crystalline forms differ considerably. The change of the electronic structure on crystallization is not direct, but is realized through the intermediate state whose electronic structure differs from that of glasses and crystals.     

Ca8Mg（SiO4）4Cl2∶Eu2+,Ce3+,Mn2+绿色荧光粉发光性能及其应用研究

利用高温固相法,合成出Eu2+、Ce3+、Mn2+共掺的Ca8Mg(SiO4)4Cl2系列绿色荧光粉。通过XRD表征了这些荧光粉的结构,通过分子荧光光谱仪研究了它们的室温发光性能。首先调查了Eu2+掺杂的Ca8Mg(SiO4)4Cl2绿色荧光粉发光性能,随后引入Ce3+、Mn2+提高了Ca8Mg(SiO4)4Cl2∶Eu2+在紫外光区的吸收强度及绿光发射强度。最后将筛选出来的荧光粉与InGaN-LED芯片组装制作成单一绿光LED器件,利用Ca7.8215MgSi4O16Cl2∶0.0525Eu2+,0.056Ce3+,0.070Mn2+所制作成的绿光LED器件发光最强,在20mA电流激发下,此LED发很强的绿光,其电致发光光谱所对应的色坐标值为:x=0.26,y=0.55。     

Synthesis and X-ray structural investigation of K8[(UO2)2(C2O4)2(SeO4)4] · 2H2O

Single crystals of the compound K₈[(UO₂)₂(C₂O₄)₂(SeO₄)4] · 2H₂O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 14.9290(4) ?, b = 7.2800(2) ?, c = 15.3165(4) ?, β = 109.188(1)°, V = 1572.17(7) ?³, space group P2₁/n, Z = 2, and R = 0.0297. The uranium-containing structural units of crystals I are dimers of the composition [(UO ₂)₂(C₂O₄)₂(SeO₄)₄]⁸⁻, which belong to the crystal-chemical group AB ⁰¹ B ² M ¹ (A = UO₂²⁺, B ⁰¹ = C₂O₄²⁻, B ² = SeO₄²⁻, M ¹ = SeO₄²⁻) of the uranyl complexes. The [(UO₂)₂(C₂O₄)₂(SeO₄)₄]⁸⁻ dimers are joined into a three-dimensional framework through electrostatic interactions with the outer-sphere potassium cations. Original Russian Text ? L.B. Serezhkina, E.V. Peresypkina, A.V. Virovets, A.G. Verevkin, D.V. Pushkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 1, pp. 68–71.     

Synthesis and structure of {NH2(C2H5)2}2[(UO2)2(C2O4)(CH3COO)4] · 2H2O

Single crystals of the compound {NH₂(C₂H₅)₂}₂[(UO₂)₂C₂O₄(CH₃COO)₄] · 2H₂O (I) are synthesized, and their structure is investigated using X-ray diffraction. Compound I crystallizes in the monoclinic system with the unit cell parameters a = 9.210(2) ?, b = 14.321(3) ?, c = 12.659(3) ?, β = 105.465(13)°, V = 1609.2(6) ?³, space group P2₁/c, Z = 2, and R = 0.0198. The structural units of crystals I are binuclear groups of the composition [(UO₂)₂C₂O₄(CH₃COO)₄]²⁻ with an island structure, which belong to the crystal-chemical group A ₂ K ⁰² B ₄⁰¹ (A = UO₂²⁺, K ⁰² = C₂O₄²⁻, B ⁰¹ = CH₃COO⁻) of the uranyl complexes, diethylammonium cations, and water molecules. The uranium-containing groups are joined into a three-dimensional framework through electrostatic interactions with diethylammonium cations and a system of hydrogen bonds, which are formed with the participation of the atoms involved in the composition of the water molecules, oxalate ions, acetate ions, and diethylammonium cations. Original Russian Text ? L.B. Serezhkina, A.V. Vologzhanina, N.A. Neklyudova, V.N. Serezhkin, 2009, published in Kristallografiya, 2009, Vol. 54, No. 1, pp. 65–67.     

Investigations of 2-Thiazoline-2-thiol as a Ligand: Synthesis and X-ray Structures of [Mn2(CO)7(μ-NS2C3H4)2] and [Mn(CO)3(PPh3)(κ2-NS2C3H4)]

Abstract  Treatment of Mn₂(CO)₁₀ with 2-thiazoline-2-thiol in the presence of Me₃NO at room temperature afforded the dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) in 51 and 34% yields, respectively. Compound 1 was quantitatively converted into 2 when reacted with one equiv of Me₃NO. Reaction of 1 with triphenylphosphine at room temperature furnished the mononuclear complex [Mn(CO)₃(PPh₃)(κ ²-NS₂C₃H₄)] (3) in 66% yield. All three new complexes have been characterized by elemental analyzes and spectroscopic data together with single crystal X-ray diffraction studies for 1 and 3. Compound 1 crystallizes in the orthorhombic space group Pbca with a = 12.4147(2), b = 16.2416(3), c = 19.0841(4) ?, β = 90°, Z = 8 and V = 3848.01(12) ?³ and 3 crystallizes in the monoclinic space group P 2₁/n with a = 10.41730(10), b = 14.7710(2), c = 14.9209(2) ?, β = 91.1760(10)°, Z = 4 and V = 2295.45(5) ?³. Graphical Abstract  Two new dimanganese complexes [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] (1) and [Mn₂(CO)₆(μ-NS₂C₃H₄)₂] (2) were formed when [Mn₂(CO)₁₀] was treated with 2-thiazoline-2-thiol in the presence of Me₃NO. Compound 2 reacts with PPh₃ to give the monomeric complex [Mn(CO)₃(PPh₃ )(κ ²-NS₂C₃H₄)]. The structures of 1 and 3 were established by crystallography. Shishir Ghosh, Faruque Ahmed, Rafique Al-Mamun, Daniel T. Haworth, Sergey V. Lindeman, Tasneem A. Siddiquee, Dennis W. Bennett, Shariff E. Kabir Investigations of 2-thiazoline-2-thiol as a ligand: Synthesis and X-ray structures of [Mn₂(CO)₇(μ-NS₂C₃H₄)₂] and [Mn(CO)₃ (PPh3)(κ ²-NS₂C₃H₄)].