Papers by Keyword: Tetragonal Phase

Abstract: Recently, the researchers gave a great interest in the superconducting topic, as the preparation method is importance to reach a high critical temperature. In this study, the Bi₂Sr₂Ca₂Cu₃O₁₀ (Bi-2223) compound prepared by thermal treatment method at different sintering temperatures such as (600, 700, 850) °C at (7) PH for (20 hrs). The phase formation was observed by X-ray diffraction, as well as information about the crystal structure, as the peaks were almost identical to the international standard document. the peaks are well indexed by tetragonal phase of Bi-2223. The results of the electrical resistance test showed that there is a difference in the critical temperature depending on the difference of the sintering temperatures The best result was at a temperature of 850 ° C. The sizes of the nanoparticles ranged from (22 - 123) nm, this is what the TEM measurements showed. It has been shown to be a successful method for preparing superconducting nanoparticles as (Bi-2223) compound

Abstract: Zirconium alloys are mostly served as the cladding materials in water reactors. Corrosion is one of the concerning problems in zirconium utilization. Transition of corrosion occurs every 2~3 μm in thickness, but its mechanism is not confirmed. To study the influence of water chemistry and the mechanism behind transition, a new type of zirconium cladding was tested for three corrosion conditions: the pure water, LiOH solution, LiOH/H₃BO₃ solution at 360°C/18.6MPa. For all cases, Zr-0.5Sn-0.15Nb-0.5Fe-0.2V cladding had a lower corrosion rate and a longer transition time than N36 cladding. The corrosion results showed that the corrosion rate was the highest and the transition time was the shortest in LiOH solution. Oxide phase information on the oxidized surface was obtained by Raman study. Tetragonal zirconia, embedded in the surface, was found at the beginning of corrosion. As the corrosion time increased, tetragonal phase stress was almost released and the content of tetragonal phase was also decreased to zero at the transition point. Stable tetragonal phase was found on the samples corroded in pure water. However, in LiOH solution, it was eliminated the quickest. The acceleration of transition in LiOH solution is partly resulted from the fast transformation of tetragonal phase. The reason for the longer transition time in N2 cladding can be directly attributed to the smaller decrease of the tetragonal phase.

Abstract: First-principles plane wave pseudopotential method based on the density functional theory is used to study of the evolution rule of the optical properties and electronic structure for ZnO tetragonal phase under different pressure. The results show that the chemical bond between zinc and oxygen is shortened with the increase of the external pressure, while the increase of orbital hybridization between the zinc atom and the oxygen atom. The calculations also show that the band structure of ZnO tetragonal phase changes with the increase of the pressure, and the band gap is broadened, which causes that the optical absorption margin and the optical absorption peak move to the direction of high energy.

Abstract: A new solid base, mesoporous K₂O-MgO/ZrO₂-La₂O₃, was prepared by hydrothermal and immersion process using a cationic surfactant C₁₆H₃₃(CH₃)₃NBr (CTAB) as template．The samples were characterized by N₂ adsorption-desorption, X-ray diffraction(XRD), Raman spectroscope and CO₂ temperature programmed desorption(CO₂-TPD). XRD and Raman spectra indicated that the catalyst calcined at 600°C and 700 °C remained surface and bulk tetragonal phase and good mesoporous characteristics when the content of K₂O is less than 0.5. While the monoclinic phase is appeared on catalyst surface when the content of K₂O is more than 0.5 calcined at 700 °C. CO₂-TPD proves that there are two adsorption states at high temperature corresponding to super alkaline sites of K₂O and undecomposed KNO₃. The catalyst with 0.4 mol ratio of K₂O to ZrO₂ calcined at 700 °C showed higher activity in the synthesis of di-2-ethylhexyl carbonate (DEHC) from dimethyl carbonate (DMC) and 2-ethylhexanol (EHOH).

Abstract: The theoretical method of predicating second and third order elastic constants of cubic and tetragonal material are presented by using first-principles total-energy method combined with the means of homogeneous deformation. The predicted results of SrTiO₃ provide reasonable agreement with the reported experimental data, other theoretical results and Cauchy relations. Since high order elastic constants are very difficult to be measured, the methods presented here provide a valuable guidance for experiments and the investigation of high order elastic properties for cubic and tetragonal materials.

Abstract: Electronic structure and chemical bonding in tetragonal KNbO3 have been studied by first-principles calculations. The band gap is indirect and a value of 1.64 eV was determined. Chemical bonding feature shows that a significant hybridization between Nb 4d and O 2p states. The bonding between K and NbO3 is mainly ionic nature while covalent nature was confirmed between Nb and O.

Abstract: The tetragonal phase CuInS₂ nanoparticles were synthesized by the reaction of Cu(Ac)₂, InCl₃·4H₂O and thioacetamide by hydrothermal method at 200 °C for 6 h in pH 1. The products were characterized by X-ray diffraction, energy-dispersive X-ray spectrum, X-ray photoelectron spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) techniques. Experimental results indicate that reaction temperature and the pH of solution are the important factors in the formation of CuInS₂. The SEM and TEM results illuminated that the CuInS₂ was composed of so many nanoparticles.

Abstract: Zirconia (ZrO2) films were deposited by metal-organic chemical vapor deposition (MOCVD) on {1 0 0} Si single crystal using Zr(thd)4 precursors. The thickness of obtained films is typically of 3.5 μm. The samples have been characterized by Field-Emission-Gun Scanning Electron Microscopy (FEG-SEM) for morphologic and microstructure study, and by X-ray Diffraction (XRD) for crystalline structure. The microstructure analysis showed that unexpected stable single tetragonal phase preferentially grew in low temperature area. According to the literature, the tetragonal phase stabilization is related to the crystalline size and the internal compressive stress. To analyze the effect of grain size and internal stress on the phase transformation, the thermal annealing were carried out in different temperatures and internal stress was measured by XRD method.

Abstract: Quantitative analysis of tetragonal phase in barium titanate powders and fundament of standard curve was discussed from the result of X-ray diffraction (XRD) experiment via testing the standard series prepared powder samples. Some different conclusions compared with the past researches were drawn by analyzing the XRD data including the integrated intensity of a certain diffraction peak, difference in 2θ between peak (002) and (200) △2θ and d (interplanar spacing) value. Thus a useful method was provided for quantitative analysis tetragonal phase in barium titanate powders by synthesized by hydrothermal method.