Search results for "Phase boundary"
showing 10 items of 41 documents
Complex structural contribution of the morphotropic phase boundary in Na0.5Bi0.5TiO3 - CaTiO3 system
2019
Abstract The correlation between structure and dielectric properties of lead-free (1-x)Na0.5Bi0.5TiO3 - xCaTiO3 ((1-x)NBT - xCT) polycrystalline ceramics was investigated systematically by X-ray diffraction, combined with impedance spectroscopy for dielectric characterizations. The system shows high miscibility in the entire composition range. A morphotropic phase boundary (MPB), at 0.09 ≤ x
Structure and dielectric properties at phase transition of Na1/2Bi1/2TiO3-BaTiO3 solid solutions
2016
ABSTRACTPhase coexistence region is studied by x-ray diffraction for Na1/2Bi1/2TiO3-BaTiO3 solid solutions in the tetragonal phase side from the morphotropic phase boundary. The first order ferroelectric phase transition, determined from a jump in the temperature dependence of dielectric permittivity, is located inside the coexistence region of cubic and tetragonal phases and is below the temperature, where tetragonality disappears. At low BaTiO3 concentrations phase transition into ferroelectric state at cooling is slowly approached in time and is smeared over large temperature range. Rietveld method, applied for more precise evaluation of phase content, reveals large local deformations in…
Critical end point behaviour in a binary fluid mixture
1997
We consider the liquid-gas phase boundary in a binary fluid mixture near its critical end point. Using general scaling arguments we show that the diameter of the liquid-gas coexistence curve exhibits singular behaviour as the critical end point is approached. This prediction is tested by means of extensive Monte-Carlo simulations of a symmetrical Lennard-Jones binary mixture within the grand canonical ensemble. The simulation results show clear evidence for the proposed singularity, as well as confirming a previously predicted singularity in the coexistence chemical potential [Fisher and Upton, Phys. Rev. Lett. 65, 2402 (1990)]. The results suggest that the observed singularities, particula…
Heterogeneous and homogeneous crystal nucleation in a colloidal model system of charged spheres at low metastabilities
2011
We have studied the nucleation kinetics in the bulk as well as at the container walls of a charged sphere colloidal model system under salt-free conditions close to the fluid–crystal phase boundary. We determined time resolved nucleation rate densities for heterogeneous nucleation on the wall, the corresponding nucleation rate densities for homogeneous nucleation and compare the resulting nucleation barrier heights. The homogeneous barrier height decreases exponentially with increasing metastability, while the heterogeneous barrier displays a sharp transition from a constant value close to the phase boundary to zero at higher metastability. As a consequence the microstructure evolution is d…
High-Pressure High-Temperature Stability and Thermal Equation of State of Zircon-Type Erbium Vanadate.
2018
Inorganic chemistry 57(21), 14005 - 14012 (2018). doi:10.1021/acs.inorgchem.8b01808
Equation of state and high-pressure/high-temperature phase diagram of magnesium
2014
The phase diagram of magnesium has been investigated to 211 GPa at 300 K, and to 105 GPa at 4500 K, by using a combination of x-ray diffraction and resistive and laser heating. The ambient pressure hcp structure is found to start transforming to the bcc structure at ∼45 GPa, with a large region of phase-coexistence that becomes smaller at higher temperatures. The bcc phase is stable to the highest pressures reached. The hcp-bcc phase boundary has been studied on both compression and decompression, and its slope is found to be negative and steeper than calculations have previously predicted. The laser-heating studies extend the melting curve of magnesium to 105 GPa and suggest that, at the h…
Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions
2019
Melting curve and phase diagram of vanadium under high-pressure and high-temperature conditions We report a combined experimental and theoretical study of the melting curve and the structural behavior of vanadium under extreme pressure and temperature. We performed powder x-ray-diffraction experiments up to 120 GPa and 4000 K, determining the phase boundary of the body-centered cubic-to-rhombohedral transition and melting temperatures at different pressures. Melting temperatures have also been established from the observation of temperature plateaus during laser heating, and the results from the density-functional theory calculations. Results obtained from our experiments and calculations a…
Detection of morphotropic phase boundary in A-site/Ca-substituted Na0.5Bi0.5TiO3 complex oxides ferroelectric system
2020
Abstract Vibrational and structural properties of lead-free piezoelectric (1-x)Na0.5Bi0.5TiO3–xCaTiO3 (0 ≤ x ≤ 1.00) solid solutions have been investigated using Raman spectroscopy and X-ray diffraction. Different anomalies were detected and analyzed taking into consideration the phase transition from rhombohedral to orthorhombic phase at room temperature. All Raman bands were interpreted through the variation in the peak positions (frequency) and the corresponding half-widths at half maximum (HWHM) as a function of x. XRD used as a complementary technique to Raman spectroscopy, showed that the rhombohedral – orthorhombic phase transition went gradually through an intermediate phase consist…
Structure and Dielectric Properties of Na1/2Bi1/2TiO3-BaTiO3Solid Solutions
2013
Dielectric properties, polarization and x-ray diffraction are studied for (1-x)Na1/2Bi1/2TiO3-xBaTiO3 solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO3. Stability of the relaxor state decreases with increasing BaTiO3 concentration, but only for compositions with low Na1/2Bi1/2TiO3 content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO3, occurs. Mechanisms, which influence the change of th…
Phase boundary dynamics of bubble flow in a thick liquid metal layer under an applied magnetic field
2020
Dynamic neutron radiography is used to observe the effect of a transverse magnetic field on argon bubbles rising through a thick layer of liquid gallium without interactions with the container walls.