Search results for "Phase Transition"
showing 10 items of 1281 documents
Shock phenomena in baryonless strongly interacting matter.
1987
Shock phenomena associated with the quark-to-hadron matter phase transition are studied using the concept of adiabats. To allow for an analysis of a medium with vanishing baryon density, the shock and Poisson adiabats are formulated in terms of hydrodynamic fluxes, rather than only thermodynamic variables. The bag-model equation of state is used to describe the phase transition. It is shown that deflagrations from the quark phase above the critical temperature and strong detonations from the supercooled quark phase to the superheated hadron phase are unlikely. Instead the possibility of weak condensation detonations from the supercooled quark phase to a mixed phase is indicated. Strong deto…
Structural and Magnetic Dynamics in the Magnetic Shape Memory Alloy Ni$_2$MnGa
2014
Magnetic shape memory Heusler alloys are multiferroics stabilized by the correlations between electronic, magnetic and structural order. To study these correlations we use time resolved x-ray diffraction and magneto-optical Kerr effect experiments to measure the laser induced dynamics in a Heusler alloy Ni$_2$MnGa film and reveal a set of timescales intrinsic to the system. We observe a coherent phonon which we identify as the amplitudon of the modulated structure and an ultrafast phase transition leading to a quenching of the incommensurate modulation within 300~fs with a recovery time of a few ps. The thermally driven martensitic transition to the high temperature cubic phase proceeds via…
Queuing transitions in the asymmetric simple exclusion process
2003
Stochastic driven flow along a channel can be modeled by the asymmetric simple exclusion process. We confirm numerically the presence of a dynamic queuing phase transition at a nonzero obstruction strength, and establish its scaling properties. Below the transition, the traffic jam is macroscopic in the sense that the length of the queue scales linearly with system size. Above the transition, only a power-law shaped queue remains. Its density profile scales as $\delta \rho\sim x^{-\nu}$ with $\nu={1/3}$, and $x$ is the distance from the obstacle. We construct a heuristic argument, indicating that the exponent $\nu={1/3}$ is universal and independent of the dynamic exponent of the underlying…
Unveiling the role of the lone electron pair in sesquioxides at high pressure: compressibility of β-Sb2O3
2021
The structural, vibrational and electronic properties of the compressed beta-Sb2O3 polymorph, a.k.a. mineral valentinite, have been investigated in a joint experimental and theoretical study up to 23 GPa. The compressibility of the lattice parameters, unit-cell volume and polyhedral unit volume as well as the behaviour of its Raman- and IR-active modes under compression have been interpreted on the basis of ab initio theoretical simulations. Valentinite shows an unusual compressibility up to 15 GPa with four different pressure ranges, whose critical pressures are 2, 4, and 10 GPa. The pressure dependence of the main structural units, the lack of soft phonons, and the electronic density char…
High pressure phase transitions in NdVO4
2015
Raman-scattering measurements on NdVO4 suggest a pressure-induced zircon to monazite phase transition beyond 5.9 GPa. The monazite phase undergoes a second phase transition to a yet unknown phase at 18.1 GPa. Lattice-dynamics calculations well support the experimental findings and predict a possible orthorhombic structure for the post-monazite structure of NdVO4.
Heat Capacity and Dielectric Properties of the PNN-PT Ferroelectric Ceramics
2012
A study of dielectric permittivity and heat capacity of the (1-х)PbNi1/3Nb2/3O3 – хPbTiO3 solid solution system (x = 0.3, 0.4, 0.5) within the 290–700 K range is reported. Temperatures of phase transitions Tm determined from maximums of dielectric permittivity ϵ depends on the content of PbTiO3. A broad phase transition is shown to proceed in the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3 composition around 312 K. Specific to phase transitions anomalous heat capacity is observed at Т ≈ 520 K in all compositions studied.
Thermal properties of ferroelectric 0.7PbNi1/3Nb2/3O3–0.3PbTiO3ceramics
2013
A study of heat capacity as function of temperature of the 0.7PbNi1/3Nb2/3O3–0.3PbTiO3 solid solution within the 120–800 K range is reported. Broad anomalies on the curve of heat capacity are revealed in the 250–450 K and 450–650 K intervals peaking at 520 K and a λ-anomaly at T ≈ 225 K. Results are discussed with account for dielectric and structural data.
Electrophoretic mobility of electrostatically interacting colloidal spheres
2004
We have measured the electrophoretic mobility μ = vE/E (where E is the electric field strength and vE the electrophoretic velocity) of highly charged colloidal spheres in deionized aqueous suspension at particle number densities n between 0.15 and 150 µm−3. Under these conditions the system exhibits fluid or crystalline order. We used laser Doppler velocimetry to determine the electrophoretic velocities vE as spatially averaged particle velocities from both integral and spatially resolved measurements. With this approach we were for the first time able to extend measurements far into the crystalline region of the phase diagram. We found μ to be constant at low n while at large n we observe …
Surface phase transitions at O and CO catalytic reaction on Pd(111)
2006
Abstract The model has been proposed to simulate numerically the reaction O + CO → CO2 and occurring phase transitions on Pd(1 1 1) surface. We calculate the phase diagram for this system by kinetic Monte Carlo method. It shows the phase transitions p ( 2 × 2 ) O → 3 × 3 R 30 O ° and p ( 2 × 2 ) O → 3 × 3 R 30 O ° → p ( 2 × 1 ) O with increase of CO coverage for room and intermediate temperatures, respectively, while in the low temperature limit the direct p(2 × 2)O → p(2 × 1)O phase transition is observed. We demonstrate that the reaction rate is the crucial factor determining the occurrence of the p(2 × 1)O phase and vanishing of the 3 × 3 R 30 O ° with decrease of temperature. The result…
Reflection high energy electron diffraction as a tool in cluster deposition experiments
2010
Reflection high energy electron diffraction (RHEED) is used to study the structure and orientation of mass-filtered iron clusters upon deposition ontoW(110). The present setup enables in situ investigations during deposition and thermal annealing. Particles as small as 2 nm at low density on the surface can be studied. The experiments reveal that larger particles with a diameter of about 13 nm are randomly oriented on the substrate with a preferred tendency to rest on their surface facets. Thermal annealing leads to a partial realignment and a significant flattening of the particles. In contrast 2 nm particles are found to align spontaneously in an epitaxial manner on W(110). Thermodynamic …