Papers by Keyword: Phase Transition

Abstract: The Solid Solution of ZrO₂ : Cdo Was Prepared by the Conventional Solid-State Reaction. Effect of Dopant Concentration on the Electrical Conductivity of ZrO₂ Was Studied for Different Compositions at Different Temperatures. the Conductivity Increases with the Addition of Cdo due to the Migration of Vacancies. the Conductivity Increases with Rise in Temperature up to 180°C and Thereby Decreases due to the Collapse of Fluorite Framework. A Second Rise in Conductivity at High Temperature beyond 460°C Is due to the Phase Transition of ZrO₂ from Monoclinic to Tetragonal. DSC, X Ray Powder Diffraction, Impedance Measurements and FTIR Spectral Studies Were Carried Out for Confirming the Doping Effect and Transitions in ZrO₂. the Addition of Cdo to Zro2 Shifted the Phase Transition of ZrO₂ to Higher Temperatures as Confirmed by the DSC Results. the Occurrence of Single Semi Circle with a Low Frequency Inclined Spike Indicates that the Conductivity Is Mainly due to the Movement of Oxide Ions.

Abstract: A novel series of ceramic samples La₂Mo_2-xTi_xO_9-δ (x = 0, 0.025, 0.05, 0.075) were prepared by solid-state reaction method. Their structures and phase transitions were studied by XRD, DSC and CTE. Their Electrical conductivities and oxygen ion transport numbers were measured by AC impedance spectroscopy at 773~1073 K and EMF at 673~1073 K, respectively. Results showed that even when x=0.075, the sample was almost pure oxygen ion conductor under the oxygen partial pressure gradient of 1.0 atm/0.21 atm, and though all the Ti-doped samples still underwent α/β structure transition, no abrupt change in the electrical conductivity was observed accompanying with the transition. They exhibited considerably higher electrical conductivity than La₂Mo₂O₉, especially at 773~873 K and the conductivity increased with increasing x value. The value of conductivity for La₂Mo_1.925Ti_0.075O_9-δ reached 8.5×10^-3 S•cm^-1 at 773 K and 0.08 S•cm^-1 at 1,073 K.

Abstract: A newly developed water-soluble azobenzene-containing monomer, 4-(4-((4- ethoxyphenyl)diazenyl)phenoxy)-N-(2-(methacryloyloxy)ethyl)-N,N-dimethylbutan-1-aminium bromide (assigned to M), was synthesized, and then a thermo-/light-sensitive gel was prepared by copolymerization of M and N-isopropylacrylamide. The properties of the gel were subsequently investigated by DSC, UV-vis, and gravimetry. The results showed that the copolymer hydrogel had a very quickly tran-cis photoisomerization rate upon UV irradiation. The critical solution temperature (CST) of the copolymer hydrogel could be toned by the M content and U, did also of the swelling ability.

Abstract: The influence of amylose and amylopectin characteristics on phase transition of cornstarches under shearless condition was observed by SEM and CLSM. The change of internal structure of starch granules during heating were directly observed online. Brightness of starch granule indicates the degree of gelatinization. The brightness of all the starches decreased with increasing temperature, this change being initiated at the centre of granule. Thus it is clear that the gelatinization process starts at the hilum of the granules. The central area of the granule around the hilum is believed to be the least organized region. The granules of waxy maize and normal maize starch subsequently break through at their cavity and channels, when the granules became swollen during gelatinization, whilst the granules of G50 and G80 remain granular and break down to smaller pieces.

Abstract: The melting temperature-pressure phase diagram [T_m(P)-P] for corundum (Al₂O₃) is predicted through the Clapeyron equation where the pressure-dependent volume difference is modeled by introducing the effect of surface stress induced pressure. Al₂O₃ has been employed to test the reliability of the model, because of its important role. Al₂O₃ has been extensively investigated because of its widely ranging industrial applications. This includes applications as a refractory material both of high hardness and stability up to high temperatures, as a support matrix in catalysis.

Abstract: ZrO2-ZrW2O8 diphasic composites with controllable coefficients of thermal expansion (CTEs) are synthesized by rapid in-situ reactive sintering with ZrO2 and WO3 as reactants. High density of ZrO2-ZrW2O8 composites without decomposition of ZrW2O8 is obtained with Y2O3 sintering additive. The CTEs of specimen with ZrO2 to ZrW2O8 mass ratio 1:1.0, 1:1.3, 1:1.5 and 1:2.0 are measured to be about 1.20×10−6, 0.31×10−6, -0.78×10−6 and -1.13×10−6 K−1, respectively. Raman mappings demonstrate homogenous dispersions of ZrO2 and ZrW2O8 in the ZrO2-ZrW2O8 composites. In addition to the role as sintering additive, some Y3+ cations enter the lattice to substitute Zr4+ in ZrW2O8, leading to an increase in disorder and a decrease in phase transition temperature of ZrW2O8 in the composites.

Abstract: The anisotropic Ising model with competing interactions is investigated in wide temperature range and |J₁/J| parameters by means of Monte-Carlo methods. Static critical exponents of the magnetization, susceptibility, heat capacity, and correlation radius are calculated in the neighborhood of Lifshitz point. According to obtained results a phase diagram is plotted, the coordinates of Lifshitz point are defined, and a character of multicritical behavior of the system is detected.

Abstract: The MCE in MnAs and doped Mn (As,Sb) compounds with low concentration of Sb has been studied by direct investigation. It was shown that for MnAs the maximum value of MCE is ΔT = 0.28 K on heating (at 308 K) and ΔT = 0.88 K on cooling (at T = 306 K) in magnetic filed 12.5 kOe. In doped Mn (As,Sb) compounds the temperature dependence of MCE is similar to MnAs. All investigated compounds demonstrate a strong temperature and field hysteresis of magnetic properties in magnetic field less than 40 kOe. It was established that a small concentration of Sb leads to decrease of MCE hysteresis and preserves the phase transition at room temperature region.

Abstract: Physical properties of oxides RMn2O5 (R-rare earth ion) have intensively been studied for the last 15 years. Lately, an increased attention has been drawn to such systems in connection with the discovery in them of a strong relation between long magnetic order and electrical polarization.

Abstract: The magnetic properties of trigonal Nd_0.6Dy_0.4Fe₃(BO₃)₄ substituted compound with the competitive Nd-Fe and Dy-Fe exchange interactions have been investigated. It has been shown that in Nd_0.6Dy_0.4Fe₃(BO₃)₄ a spontaneous spin-reorientation transition from an ease-axis state to an easy-plane occurs near 31 K. Anomalies of the magnetization curves are observed in a spin-flop transition induced by the magnetic field B||c. The calculations were performed using a molecular-field approximation and a crystal-field model for the rare-earth subsystem. Extensive experimental data on the magnetic properties of Nd_0.6Dy_0.4Fe₃(BO₃)₄ have been interpreted and good agreement between theory and experiment has been achieved using the obtained theoretical dependences.