Papers by Keyword: Phase Transition

Abstract: Y₂O₃ has a great application potential at reaction barrier coating of high-temperature composites due to its high thermodynamic stability and high melting point, and the phase structure stability at high temperature and structure dependent mechanical property are key parameters for this application. Y₂O₃ thin films were deposited on silicon (100) wafers by DC magnetron sputtering with various oxygen partial pressure and substrate bias, and then vacuum annealing at 1000°C was performed to investigate the phase structure stability. The microstructure, stress and hardness of as-deposited and annealed Y₂O₃ thin films were explored by X-ray diffraction, transmission electron microscope, and nanoindenter. The result showed that as-60 bias voltage was applied to substrate, cubic-c phase formed regardless of variation of oxygen partial pressure, and the cubic-c phase remains stability and crystallinity became better after annealing at 1000 °C.In addition, the hardness and modulus also just had minor changes as a function of oxygen partial pressure. As oxygen partial pressure was kept at 0.043 Pa, phase transition from cubic-c to monoclinic-b phase took place with increasing substrate bias, accompanying by the increment of hardness and modulus, and 1000 °Chigh-temperature annealing resulted in that as-deposited monoclinic-b phase transforms to cubic-c phase.

Abstract: Lead-free Ba_0.9Ca_0.1Sn_0.06Ti_0.94-xZr_xO₃ (BCTSZ) ceramics where x = 0.00, 0.03, 0.05, 0.07 and 0.09 were prepared by the conventional solid-state reaction method. The dielectric constant of the Zr doped BCTS ceramic was enhanced by Zr incorporation. The maximum dielectric constant were obtained at the composition of x = 0.05. The dielectric property investigation indicated that the degree of the diffuse phase transition behavior increased with Zr substitution. Phase transition of tetragonal to cubic structure was significantly dependent on the amount of Zr added.

Abstract: Samples of partly desorbed MgH₂ have been studied by the X-ray diffraction method. All samples contained two phases (Mg and MgH₂) and were stable at ambient condition for several months. After fast quenching in liquid nitrogen the samples became unstable and transformed after several days into Mg. The rate of decomposition depends on the amount ratio of Mg and MgH₂ phases in the sample. Destabilization of the hydride phase observed in quenched samples can be explained on the basis of different diffusion of disordered and ordered hydrogen atoms.

Abstract: The crystal structural, mechanical and thermal properties of U_XLa_1-XS compound with different concentrations (x= 0.00, 0.08 and 0.40) are investigated using modified inter-ionic potential theory (MIPT), which parametrically includes the effect of coulomb screening by the delocalized f-electrons. Our calculated values of phase transition pressure, bulk modulus and volume change are agree well with the theoretical and experimental data. We have also calculated the second order elastic constants and Debye temperature of these three concentrations.

Abstract: We have investigated the pressure induced phase transition of InP from ZB to NaCl structure associated by using realistic interaction potential model (RIPM), which is modified by taking effect of temperature. This model consists of coulomb interaction, three body interaction, and short range overlap repulsive interaction up to second nearest neighbour. Phase transition pressure is associated with a sudden collapse in volume showing the incidence of first order phase transition. The phase transition pressure and associated volume collapses obtained from present model show a generally good agreement with the available experimental and theoretical data.

Abstract: In the present paper we have calculated the phase transition and volume collapse of Samarium Bismuthide under pressure using a three body interaction potential model which includes long range columbic interaction, three body interactions and short range overlap repulsive interaction operative up to second nearest neighbour. This compound undergoes transition from NaCl structure to body-centred tetragonal (BCT) structure (distorted CsCl-type P4/mmm). Our calculated results of phase transitions and volume collapses of SmBi are found to be close to the experimental results.

Abstract: The structural properties of rare earth compound in NaCl-structure are studied in the present investigation. To study these properties of erbium telluride (ErTe), the Realistic Interaction Potential Approach (RIPA) model has been used. Present compound shows NaCl-type to CsCl-type structural phase transformation. The structural properties, including phase transition pressure and volume collapse are obtained and compared with available literature. The calculated equilibrium structural parameters are in good agreement with the available experimental and theoretical results. Further more to study the electronic properties, band structure and density of state are reported.

Abstract: In the present work structural and mechanical properties of ThC and ThO compounds have been carried out using desirable modified inter-ionic potential theory (MIPT), which parametrically includes the effect of Coulomb screening. The transition from rock salt to caesium chloride occurs around 40.0 GPa and 65.0 GPa in the case of ThC and ThO respectively. We have also calculated bulk (B₀), Young (E), and shear moduli (G), Poisson ratio (υ) and anisotropic ratio (A) in NaCl-type structure for these compounds and differentiate them with other experimental and theoretical results which show a good agreement.

Abstract: We develop a phase field model that describes the elastic distortion of a ferroelastic material with cubic anisotropy due to an arbitrary dislocation network and a uniform external load. The dislocation network is characterized using the Nye tensor and enters the formulation via a set of incompatibility constraints for the internal strain field. The long-range elastic response of the material is obtained by minimization of the free energy that accounts for higher order terms of the order parameters and symmetry-adapted strain gradients. To demonstrate the performance of the model, a minimal version of continuum dislocation dynamics is used to investigate the simultaneous evolution of the network of geometrically necessary dislocations and the internal strain field.

Abstract: The issue of HMX phase transition under hydrostatic compression is not clear and experiments show conflicting results. Effective solution via first-principles simulation is challenged by difficulty of accurate prediction of Van der Waals interaction, which exists ubiquitously and is crucial for determining the structure of molecules and condensed matter. We have contributed to this by constructing a set of pseudopotentials and pseudoatomic orbital basis, specialized for molecular systems with C/H/N/O elements. The reliability of the method is verified from the interaction energies of 45 complexes (comparing to the results of coupled cluster with singles and doubles (Triple) (CCSD)(T)) and the crystalline structures of 7 typical explosives (comparing to experiments). Using this method, we complete the phase diagram of HMX under static compression up to 50 GPa. We make it clear that no β→δ/ε→δ phase transition occurs at 27 GPa, which has long been a hot debate in experiments. A possible γ→β phase transition is found at around 2.10 GPa in the environment of vapour. We have also predicted the equation of states for α-, δ-, and γ-HMX, which are experimentally absent.