Crystal growth and physicochemical properties of structural analogs of krupkaite

Single crystals of rare-earth analogs of the mineral krupkaite, CuPbBi₃S₆, have been prepared for the first time, and their physicochemical properties have been studied. The compounds CuYbBi₃S₆, CuEuEr₃S₆, CuYbEr₃S₆, and CuPbEr₃S₆ are isostructural with CuPbBi₃S₆ and crystallize in orthorhombic symmetry (sp. gr. Pb2₁ m, Z = 2): a = 11.204, b = 11.376, c = 3.960 Å (CuYbBi₃S₆); a = 11.244, b = 11.440, c = 3.998 Å (CuEuEr₃S₆); a = 11.30, b = 11.55, c = 4.03 Å (CuPbEr₃S₆); a = 11.236, b = 11.414, c = 3.98 Å (CuYbEr₃S₆).     

氮化镓粉末的合成及其结构性质的研究

在950℃氮化温度下,通过β-Ga2O3粉末与流动的NH3反应35min制备出GaN粉末.XRD、XPS、FTIR、TEM的测量结果表明GaN粉末是六角纤锌矿结构的单晶晶粒,其晶格常数a=0.3191nm,c=0.5192nm;在粉末表面,Ga和N两种元素比约为11;GaN晶粒的形状为棒状.     

Synthesis, structural and optical properties of Ni-doped ZnO micro-spheres

Ni doped ZnO nanoparticles were synthesized by a simple chemical method at low temperature with Ni:Zn atomic ratio from 0 to 5 %. The synthesis process is based on the hydrolysis of zinc acetate dihydrate and nickel acetate tetrahydrate followed by heat treatment at 65 °C under refluxing using methanol as a solvent. X-ray diffraction analysis reveals that the Ni-doped ZnO crystallizes in a wurtzite structure with crystal size of 4–11 nm. These nanocrystals self-aggregated themselves into hollow spheres of size of 600–170 nm. High resolution transmission electron microscopy image shows that each sphere is made up of numerous nanoparticles of average diameter 4 nm. The XRD patterns, Scanning electron microscopy and transmission electron microscopy micrographs of doping of Ni in ZnO are confirmed the formation of micro-spheres. Furthermore, the UV–vis. spectra and photoluminescence spectra of the Ni-doped ZnO nanoparticles were also investigated. The band gap of the nanoparticles can be tuned in the range of 3.55–3.36 eV by the use of the dopants. The observed red shift in the band gap from UV–visible analysis and near band edge UV emission with Ni doping may be considered to be related to the incorporation of Ni ions into the Zn site of the ZnO lattice.     

Synthesis,structural characterization and some properties of a germanic analogue of phillipsite

Germanic phillipsite, with the chemical formula K₂O·Al₂O₃·2GeO₂·xH₂O, has been synthesized at 90°C from K⁺ containing gels. The parameters of its primitive (tetragonal) unit cell are : $\text{a}\text{=}\text{b}\text{= 14.515}\text{A}\text{?}$ and $\text{c}\text{= 9.733}\text{A}\text{?}$. IR spectroscopy shows that all the absorption bands are shifted towards longer wavelengths. The structural stability towards ion-exchange has been followed by X-ray diffraction. Adsorption isotherms of N₂ and H₂O have been measured. The pore opening of K-germanic phillipsite is approximately 3 Å.     

Synthesis of the mineral geikielite MgTiO3

The preparation of pure geikielite, MgTiO₃, is carried out by precipitation with NaOH solution at pH 12 from solutions Ti⁴⁺/Mg²⁺ in molar ratio 1/1 M and calcination of the precipitate at 600°C in a dynamic atmosphere: heating rate 300°Ch^–1.At room temperature and a 1 KHz of frequency the dielectric constant () and the electric resistivity () were measured. The values were = 1 5.0 and = 1.1×10¹⁰ cm^–1.     

Computational mineral physics and the physical properties of perovskite

The inherent uncertainties in modern first-principles calculations are reviewed using geophysically relevant examples. The elastic constants of perovskite at lower-mantle temperatures and pressures are calculated using ab initio molecular dynamics. These are used in conjunction with seismic tomographic models to estimate that the lateral temperature contrasts in the Earth's lower mantle are 800 K at a depth of 1000 km, and 1500 K at a depth of 2000 km. The effect of Al(3+) on the compressibility of MgSiO(3) perovskite is calculated using three different pseudopotentials. The results confirm earlier work and show that the compressibility of perovskites with Al(3+) substituted for both Si(4+) and Mg(2+) is very similar to the compressibility of Al(3+)-free perovskite. Even when 100% of the Si(4+) and Mg(2+) ions are replaced with Al(3+), the bulk modulus is only 7% less than that for Al(3+)-free perovskite. In contrast, perovskites where Al(3+) substitutes for Si(4+) only and that are charge balanced by oxygen vacancies do show higher compressibilities. When corrected to similar concentrations of Al(3+), the calculated compressibilities of the oxygen-vacancy-rich perovskites are in agreement with experimental results.     

Synthesis,structural and electrical properties of SiC nanowires via a simple CVD method

The β-SiC nanowires (NWs) prepared by a simple carbon template method exhibit two kinds of electrical transport properties, depending on their crystalline structures. A part of the NWs exhibit the resistivities as low as 1.5 × 10⁻⁵ to 3 × 0⁻⁴ Ω cm due to n-type doping from the intrinsic planar defects and stacking faults, forming Ohmic contact with Au electrodes; the other ones show a typical characteristic of the semiconductor with a remarkable increase in resistivity by 5–7 magnitude orders, owing to a nearly perfect single-crystalline structure with few intrinsic defects. Additionally, the electrical breakdown behavior is observed in the metallic NWs.     

Synthesis and characterization of solar photoactive TiO2 nanoparticles with enhanced structural and optical properties

The structural, morphological, and optical properties of the sol–gel derived TiO₂ nanoparticles at different pH and calcination temperature were investigated in the present study. X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM), UV–Visible(Vis) spectroscopy, energy dispersive studies (EDS), Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray photoluminescence (PL) spectroscopy, BET surface area analysis, and Barrett-Joyner-Halenda (BJH) pore size distribution and pore volume analysis were used to characterize the prepared TiO₂ photocatalyst. The range of crystallite size and band gap of the synthesized TiO₂ samples were in the range of 20–80?nm and 2.5–3.2?eV respectively. The photocatalytic performance of prepared TiO₂ photocatalysts was evaluated by photodegradation of Methylene Blue (MB) solution under simulated solar irradiation. Results illustrate that the synthesized TiO₂ exhibits visible light activity at higher calcination temperature. Crystallinity and surface area plays a vital role in the overall performance of the prepared TiO₂ photocatalyst.     

金属掺杂二氧化锡纳米粉体的合成、结构表征及光学性能研究

以SnCl4.5H2O和MnCl2.4H2O,MgCl2.6H2O为主要原料,采用溶胶-凝胶法分别成功合成了纯二氧化锡的纳米粉体及纳米级的镁掺杂和锰掺杂的二氧化锡纳米颗粒,分别研究了掺杂不同含量的金属镁和锰的二氧化锡粉体的光谱性能。另外,通过X-射线粉末衍射仪(X-ray diffractometer,XRD)、红外光谱(IR)、紫外-可见光谱(UV-vis)、差热-热失重(DSC-TG)等多种测试手段对制备的样品晶相、热稳定性及吸收光谱进行了研究。     

Synthesis and structural, optical and electrical properties of TiO2/SiO2 nanocomposites

Sole components of titania (TiO₂), silica (SiO₂) nanoparticles, and binary TiO₂–SiO₂ nanocomposites with various molar ratios of silica contents were prepared by modified sol–gel method. The samples were calcined at 500 °C for 5 h and characterized by X-ray diffraction, Fourier transform infrared spectroscopy (FTIR), UV–Vis spectroscopy, Brunauett–Emmett–Teller (BET), and photoconductivity. The crystallite size for TiO₂/SiO₂ nanocomposites was calculated using Scherrer’s formula and found to be 5 nm for TiO₂ nanoparticles. The binary oxide shows the anatase type of TiO₂ at the mole ratio up to 80 mol% of TiO₂ added. The band gap for as-synthesized nanocomposites was calculated and it was found that the band gap decreases with increase of SiO₂ content and then decreases with excess SiO₂ content. FTIR confirms that both TiO₂ and SiO₂ phases have been formed. The BET surface area for TiO₂/SiO₂ nanocomposite is found to be 303 m²/g, and pore size distribution has an average pore diameter about 10 nm for 40 mol% of TiO₂ added. It also confirms the absence of macropores and the presence of micro and mesopores. The field-dependent dark and photoconductivity studies reveal that the dark and photocurrent increase linearly with applied field confirming the ohmic nature of the electric contacts. The dark and photocurrent increase slightly with increase of SiO₂ content and decrease with excess amount of SiO₂.     

Synthesis,structural and photoluminescence properties of SiOx nanospheres prepared by evaporation of silicon monoxide

We report synthesis of amorphous silicon oxide nano-spheres in bulk quantity by using a simple non-catalytic process based on thermal evaporation of silicon monoxide. Structural characteristics of the nano-spheres were investigated using high resolution scanning and transmission electron microscopes equipped with energy dispersive X-ray spectroscopy (EDAX). Selected area electron diffraction and EDAX analyses revealed that nano-spheres were amorphous and comprised of silicon oxide only with Si and O in an atomic ratio of ~ 1:2. Photoluminescence measurements showed that the SiO_x nano-spheres had strong emission band in the blue region. Possible growth mechanism based on vapor-solid model has been discussed. The SiO vapors generated at high temperature react with O₂ to form SiO_x vapors which subsequently condense on the substrates (placed in the appropriate temperature zone) to form SiO_x nano-spheres.     

Thorium/uranium mixed oxide nanocrystals: Synthesis, structural characterization and magnetic properties

One of the primary aims of the actinide community within nanoscience is to develop a good understanding similar to what is currently the case for stable elements. As a consequence, efficient, reliable and versatile synthesis techniques dedicated to the formation of new actinide-based nano-objects （e.g., nanocrystals） are necessary. Hence, a ＂library＂ dedicated to the preparation of various actinidebased nanoscale building blocks is currently being developed. Nanoscale building blocks with tunable sizes, shapes and compositions are of prime importance. So far, the non-aqueous synthesis method in highly coordinating organic media is the only approach which has demonstrated the capability to provide size and shape control of actinide-based nanocrystals （both for thorium and uranium, and recently extended to neptunium and plutonium）. In this paper, we demonstrate that the non-aqueous approach is also well adapted to control the chemical composition of the nanocrystals obtained when mixing two different actinides. Indeed, the controlled hot co-injection of thorium acetylacetonate and uranyl acetate （together with additional capping agents） into benzyl ether can be used to synthesize thorium/uranium mixed oxide nanocrystals covering the full compositional spectrum. Additionally, we found that both size and shape are modified as a function of the thorium：uranium ratio. Finally, the magnetic properties of the different thorium/uranium mixed oxide nanocrystals were investigated. Contrary to several reports, we did not observe any ferromagnetic behavior. As a consequence, ferromagnetism cannot be described as a universal feature of nanocrystals of non-magnetic oxides as recently claimed in the literature.     

Synthesis,structural, band gap,and optical properties of Ba3(PO4)2 hierarchical structural materials

Journal of Materials Science: Materials in Electronics - Ba3(PO4)2 structure with Rhombohedral phase was prepared by a facile wet chemical method. In this experiment, NaOH is used as a surfactant...     

Electronic and structural properties of BaTe

We present the results of a theoretical study of the structural and electronic properties of BaTe, using first principle pseudopotential plane wave (PP-PW) and full potential linear augmented plane wave (FP-LAPW) methods. In both approaches the generalized gradient approximation (GGA) was used for the exchange-correlation potential. In the case of PP-PW we repeated the calculation using local density approximation (LDA). Our calculated values for the structural parameters, metallization and structural transition pressures are in reasonable agreement with experimental results. Although the calculated band gap within GGA shows substantial improvement over LDA, it is still lower than the measured ones. There is a speculation that at least part of this discrepancy is due to the discontinuity inherent in the exchange-correlation potential. The partial contribution from each atom to the total density of states is calculated. It is seen that the lower valence bands are mainly formed by s orbitals of Te, while the upper valence bands are formed by the p orbitals of Te. Empty states of the conduction bands are mainly formed by d orbitals of Ba.     

Synthesis,structural and optical properties of nanoparticles (Al,V) co-doped zinc oxide

The synthesis by the sol–gel method, structural and optical properties of ZnO, Zn_0.99Al_0.01O (AlZ), Zn_0.9V_0.1O (VZ) and Zn_0.89Al_0.01V_0.1O (AlVZ) nanoparticles was reported. The approach was slow release of water for hydrolysis by esterification reaction followed by a supercritical drying in ethyl alcohol. After thermal treatment at 500^°C in air, the obtained nanopowders were characterized by various techniques such as transmission electron microscopy, X-ray diffraction and photoluminescence (PL) spectroscopy. The structural properties showed that the ZnO nanoparticles with an average particle size of 25 nm exhibit hexagonal wurtzite structure. From the optical studies, it was found that the optical band gap was located between 2.97 and 3.17 eV. The obtained electrical properties showed the potential application of the samples in optoelectronic devices. The powder of AlVZ presented a strong luminescence band in the visible range. The PL band energy position presented a small blue shift with the increase of measurement temperature. Different possible attributions of this emission band will be discussed.