Phase Transition Region Research Articles

Dielectric Nonlinearity and the Velocity of Ultrasonics in the Region of the Structural Phase Transition in (K0.5Na0.5)(Nb1 – xTa x )O3 Ceramics

Properties of the dielectric response of (K0.5Na0.5)(Nb1 – xTa x )O3 + 0.5 mol % MnO2 (KNN-xTa) ferroelectric ceramics at temperatures including that of the structural phase transition (SPT) from the orthorhombic phase to tetragonal is studied and compared to the behavior of elastic properties in this region of temperatures. The character is determined of the concentration dependences of such anomalies as the temperature of the maximum of permittivity Tmax(x) in the SPT region and temperature Textr at which the maximum increment of permittivity upon specimen heating in the SPT region occurs. It is found temperature Textr coincides with the one at which minimum v(T) of the velocity of a longitudinal acoustic wave is observed at SPT. Features of a nonlinear dielectric response associated with the coexistence of different types of domain boundaries in the region of a smeared structural transition in KNN-xTa ceramics are determined in studying the temperature behavior of polarization loops.

Study of phase transition of even and odd nuclei based on q-deforme SU(1,1) algebraic model

The q-deformed Hamiltonian for the SO(6)↔U(5) transitional case in s, d interaction boson model (IBM) can be constructed by using affine SUq(1,1) Lie algebra in the both IBM-1 and 2 versions and IBFM. In this research paper, we have studied the energy spectra of Xe120−128 isotopes and Xe123−131 isotopes and B(E2) transition probabilities of Xe120−128 isotopes in the shape phase transition region between the spherical and gamma unstable deformed shapes of the theory of quantum deformation. The theoretical results agree with the experimental data fairly well. It is shown that the q-deformed SO(6)↔U(5) transitional dynamical symmetry remains after deformation.

Magnetocaloric Effect in BiFe1−xZnxO3 Multiferroics

Ceramic BiFe1−xZnxO3 multiferroic samples were prepared by the solid combustion method for x = 0.1, 0.15, and 0.2. Structural, magnetic, and magnetocaloric properties of the multiferroics have been studied. For all samples, an antiferromagnetic phase transition is observed in the region of 630 K. With increase in x, the reduction in magnitude of magnetization and Neel temperature is observed. The magnetocaloric properties, entropy, relative cooling power, and heat capacity have been calculated within the framework of thermodynamic theory. It has been established that the maximum changes of magnetocaloric properties of multiferroics are observed in the region of magnetic phase transition.

Microphase Segregation of Diblock Copolymers Studied by the Self-Consistent Field Theory of Scheutjens and Fleer.

We used the self-consistent field (SCF) formalism of Scheutjens and Fleer (SF-SCF) to complement existing theoretical investigations on the phase behavior of block copolymer melts. This method employs the freely jointed chain (FJC) model for finite chain length and systematic differences exist compared to the classical SCF predictions. We focus on the critical and hexagonal (HEX) to lamellar (LAM) phase transition region at intermediate and strong segregations. Chain length (N) dependence of the critical point () was found to be . The characteristic spacing (D) of LAM was found as at the critical conditions. We present SF-SCF predictions for the phases single gyroid (SG), double gyroid (DG) and hexagonally perforated lamellar (HPL), in the region where HEX and LAM compete. At , ; we found SG and HPL were metastable with respect to LAM or HEX, DG was stable in a narrow region of the asymmetry ratio. In contrast to the latest predictions, at strong segregation , DG was found to be metastable. From the structural evolution of HPL, we speculate that this may be an intermediate phase that allows the system to go through various connectivity regimes between minority and majority blocks.

Magnetostriction of ferromagnetic shape memory alloy Ni2.27Mn0.73Ga studied in magnetic fields up to 10 T

Magnetostriction of a non-modulated martensite was measured for Ni2.27Mn0.73Ga ferromagnetic shape memory alloy in steady magnetic fields μ0H up to 10 T at temperatures below room temperature and in μ0H ≤ 1 T at temperatures above room temperature. Linearity of the longitudinal magnetostriction λ|| observed at high fields μ0H > 6 T implies that the magnetostriction is associated with a 3d electron band. The anisotropic magnetostriction obtained in a magnetic field μ0H = 1 T at T = 4.2 K is ∼16 ppm and decreases down to 3 ppm with the increase in temperature. The volume magnetostriction is positive but very small (∼0.6 ppm) under these conditions. In the region of the magnetostructural phase transition the longitudinal and volume magnetostriction showed a complex sigh-changing behavior which depends on the strength of applied magnetic field. Thermal expansion coefficient α of Ni2.27Mn0.73Ga in the martensitic state was measured to be α ∼13 × 10−6 K−1 which is comparable with the thermal expansion coefficient of a non-stoichiometric Ni2.19Mn0.81Ga single crystal.

Assessing the Thermal Conductivity of Cu2−xSe Alloys Undergoing a Phase Transition via the Simultaneous Measurement of Thermoelectric Parameters by a Harman-Based Setup

Some materials such as Cu2−xSe, Cu1.97Ag0.03Se, and SnSe have attracted attention by demonstrating a significant enhancement of their thermoelectric performance, which is associated with a phase transition. This phenomenon, observed in a limited temperature (T) interval, results in sharp changes of the Seebeck coefficient (S), the electrical resistivity (ρ), and the thermal conductivity (κ), which may render the correct evaluation of the dimensionless figure of merit (ZT) difficult. We report the thermoelectric properties of a polycrystalline Cu2−xSe sample which is known to undergo a phase transition near 410 K, containing a mixture of α- and β-phases at room temperature, as determined by x-ray diffraction measurements. We have used a Harman-based setup (TEMTE Inc.), which assures the direct measurement of ZT at all temperatures, including the phase transition region. This approach ensures that κ(T) is determined under steady-state conditions at any given temperature, including points arbitrarily close to the transition temperature which cannot be guaranteed by previously used techniques such as laser flash. We have observed a sharp maximum for κ(T) near 410 K, similar to the reported specific heat variation, with a ZT peak value of 0.2 at 400 K. The expected gain in ZT related to the phase transition is reduced because the increase in S is counterbalanced by the increase in κ(T). Thus, our detailed assessment of the temperature variation of the individual thermoelectric properties accurately evaluates the performance enhancement associated to a structural phase transition and helps to elucidate this complex phenomenon.

Thermodynamic parameters of mixtures with epoxy as a component under shock wave loading

The results of numerical experiments on modeling of shock wave loading of mixtures are obtained by using thermodynamic equilibrium model TEC (thermodynamic equilibrium components) are presented. The thermodynamic parameters are modeled for the mixtures that include epoxy resin as a component. The model allows taking into account the phase transition under shock wave loading, when the substance in the region of phase transition is considered as mixture of low-pressure phase and high-pressure phase. Interest in the investigation of compressibility of such mixtures is associated as with the possibility of creating materials that have the required properties and the properties of the materials themselves. The good agreement of these model calculations with the data of different authors that defined on the experiments basis is obtained. The model allows to describe dynamic loading of solid and porous mixtures comprising epoxy resin and various components such as quartz SiO2, periclase MgO, corundum Al2O3, spinel MgAl2O4, enstatite Mg2[Si2O6].

Membranotropic action of lauric acid, fenspiride and kaoline in model lipid membranes: role of lipid composition

Background: Model lipid membranes are widely used nowadays to elucidate membranotropic action (MA) of pharmaceuticals as well as for development of liposomal drugs. Meanwhile, membrane lipid composition could substantially affect a drug-membrane interaction. Objectives: Comparision of MA of certain pharmaceuticals on model membranes with various lipid compositions. Materials and methods: By means of differential scanning calorimetry (DSC) lauric acid, fenspiride and kaolin were studied with respect of their effects on phase transitions of model membranes based on hydrated phospholipids. Along with “standard” membrane based on L-α-dipalmitoyl­phos­pha­ti­dyl­choline (DPPC), a membrane containing cerebrosides (DPPC-C) was used, as well as one composed of DPPC, L-α-dipalmitoyl­phospha­tidylethanolamine and cholesterol (DPPC-DPPE-Chol). According to literature, DPPC and DPPC-C membranes are characterized by lipid phase homogeneity, as distinct from membrane DPPC-DPPE-Chol, where two different lipid phases coexist both below and above phase transition region. Results: It was shown that fenspiride manifested similar MA on membranes of all three types. MA of lauric acid in DPPC and DPPC-C membranes were qualitatively similar, whereas, in DPPC-DPPE-Chol membrane, different effects were observed. As to kaolin, distinctions in its MA were observed even between DPPC and DPPC-C membranes, namely, elevation of phase transition temperatures in DPPC-C membrane and a tendency to their reduction in DPPC one. In DPPC-DPPE-Chol membrane, kaolin markedly lowered phase transition temperatures coupled with opposite changes in cooperativity. Conclusions: By the examples of separated substances it was shown that strong disordering MA may be practically independent on lipid composition of membrane. Lipid rearrangement and cooperativity changes in membrane can be induced not only by incorporation of guest substances in the bulk, but also by their adsorption on membrane surface.The obtained results could be useful in adjustment of model membrane composition for MA studies of different pharmaceuticals.

Определение термодинамических параметров в областях фазовых переходов в Cu-=SUB=-1.95-=/SUB=-Ni-=SUB=-0.05-=/SUB=-S

AbstractX-ray diffraction and differential thermal analysis data obtained in the Cu_1.95Ni_0.05S phase-transition region are analyzed. It is established that the low-temperature rhombic α phase in Cu_1.95Ni_0.05S transforms to the hexagonal β phase at temperatures of 370–390 K and to the cubic γ phase at temperatures of 740–765 K according to the scheme $$\alpha \to \mathop {\alpha + \beta }\limits_{370 - 390K} \to \mathop {\alpha + \gamma }\limits_{740 - 765K} \to \gamma $$ α → α + β 370 − 390 K → α + γ 740 − 765 K → γ . It is determined (using the temperature dependence of differential thermal analysis) that the transition α → β is accompanied by heat absorption while the transition β → γ is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of ~10^–20 cm^3 at temperature rates of 0.11 and 0.08 K^–1. It is demonstrated that the transition α → γ is accompanied by alternation of the structures passing through the intermediate β phase, which is incommensurate with respect to the α and γ phases.

Determination of Thermodynamic Parameters in the Cu1.95Ni0.05S Phase-Transition Regions

X-ray diffraction and differential thermal analysis data obtained in the Cu1.95Ni0.05S phase-transition region are analyzed. It is established that the low-temperature rhombic α phase in Cu1.95Ni0.05S transforms to the hexagonal β phase at temperatures of 370–390 K and to the cubic γ phase at temperatures of 740–765 K according to the scheme $$\alpha \to \mathop {\alpha + \beta }\limits_{370 - 390K} \to \mathop {\alpha + \gamma }\limits_{740 - 765K} \to \gamma $$ . It is determined (using the temperature dependence of differential thermal analysis) that the transition α → β is accompanied by heat absorption while the transition β → γ is accompanied by heat release. It is found that both transitions are allowed and belong to the reconstructive type. Both transitions are found to occur in a fluctuation volume of ~10–20 cm3 at temperature rates of 0.11 and 0.08 K–1. It is demonstrated that the transition α → γ is accompanied by alternation of the structures passing through the intermediate β phase, which is incommensurate with respect to the α and γ phases.

Неуниверсальное скейлинговое поведение ширины пиков проводимости в режиме квантового эффекта Холла в структурах InGaAs/InAlAs

AbstractThe longitudinal ρ_ xx and Hall ρ_ xy resistances were measured in the region of the quantum phase transitions for the quantum Hall effect regime with magnetic fields up to 12 T at temperatures of T = 0.4–30 K in two-dimensional electron systems n -In_0.9Ga_0.1As/In_0.81Al_0.19As. The nonuniversal scaling behavior of the temperature dependence of the width of the resistance ρ_ xx peaks related to the effect of the large-scale random potential and of Landau-level mixing with opposite spin directions was found.

Атомистическое моделирование теплофизических характеристик кремния в области фазового перехода полупроводник-металл

Атомистическое моделирование теплофизических характеристик кремния в области фазового перехода полупроводник-металл

Strange Particle Reconstruction by the Missing Mass Method

The main goal of modern heavy-ion experiments is a comprehensive study of the QCD phase diagram, in a region of Quark-Gluon Plasma (QGP) and possible phase transition to QGP phase. Strange particles produced in the collision are sensitive probes of the created media. Reconstruction of Σ particles together with other strange particles completes the picture of strangeness production. Σ+ and Σ− have all decay modes with at least one neutral daughter, which can not be registered by the CBM detector. For their identification the missing mass method is proposed: a) tracks of the mother (Σ−) and the charged daughter (π−) particles are reconstructed in the tracking system; b) the neutral daughter particle (n) is reconstructed from these tracks; c) a mass constraint is set on the reconstructed neutral daughter; d) the mother particle is constructed of the charged and reconstructed neutral daughter particles and the mass spectrum is obtained, by which the particle can be identified. The method can be applied for other strange particles too. In total 18 particle decays with neutral daughter are now included into physics analysis.

Магнитный фазовый переход в MnSi на основе LSDA+U +SO-расчетов электронной структуры и спин-флуктуационной теории

AbstractSpin states appearing near the magnetic phase transition in helicoidal ferromagnet MnSi are studied on the basis of the spin-fluctuation theory and the LSDA + U + SO calculations of the electronic structure. The temperature dependence of the uniform magnetic susceptibility is calculated near the magnetic phase transition temperature, and the result agrees well with the experiment. Spin correlators corresponding to various solutions of the equation of magnetic state are determined in the region of the magnetic phase transition expanded in temperature. It is shown that, in this region, a helicoidal short-range order appears in the form of the superposition of left and right spin spirals with stochastic weight coefficients. It is shown that the magnetic susceptibility divergences on the helicoid wave vector at the temperature of disappearance of local magnetization and during the transition to the paramagnetic state.

The competitive effect of non-magnetic defect and films thickness on the ferromagnetic critical temperature in Ising thin-films

In this work, Monte Carlo simulation was employed to investigate the competitive effect of non-magnetic defects and the thickness on the ferromagnetic behavior of Ising spins in a reduced geometry, i.e. thin-films. The magnetic properties were investigated as functions of temperature, defect concentration, and films’ thickness, especially in the ferromagnetic phase transition region. The finite size scaling was performed via the fourth order cumulant of the magnetization to extract the critical temperatures. From the results, the extracted critical temperatures agree well with previous theoretical investigation, where applicable. With increasing concentration of the nonmagnetic defects, the Ising phase-transition-point slightly shifts towards lower temperature, while the increase of films thickness enhances the critical temperature value. Being confirmed by the main-effect-plot analysis, the increase in thickness has much greater influences on the critical temperature than that of the defect concentration, which could be described in term of the average ferromagnetic interaction spin. As the role of the defect is negligence in the range of considered defect concentration (up to ten percent), it therefore suggests that the preparation of ferromagnetic films can be done in normal operating condition where defects usually occur. It may be not economically worth to aim for the perfectly smooth films when the associated application operates at temperatures away from the critical point.

Temperature anomalies of shock and isentropic waves of quark–hadron phase transition

In this work, we consider a phenomenological equation of state, which combinesstatistical description for hadron gas and a bag-model-based approach for the quark–gluon plasma. The equation of state is based on the excluded volume method in its thermodynamically consistent variant from Satarov et al [2009 Phys. At. Nucl. 72 1390]. The characteristic shape of the Taub adiabats and isentropes in the phase diagram is affected by the anomalous pressure–temperature dependence along the curve of phase equilibrium. The adiabats have kink points at the boundary of the two-phase region, inside which the temperature decreases with compression. Thermodynamic properties of matter observed in the quark–hadron phase transition region lead to hydrodynamic anomalies (in particular, to the appearance of composite compression and rarefaction waves). On the basis of relativistic hydrodynamics equations we investigate and discuss the structure and anomalous temperature behavior in these waves.

Controlling the phase transition in nanocrystalline ferroelectric thin films via cation ratio.

Traditionally, the ferroelectric Curie temperature can be manipulated by chemical substitution, e.g., in Ba1-xSrxTiO3 as one of the archetypical representatives. Here, we show a novel approach to tune the ferroelectric phase transition applicable for nanostructured thin films. We demonstrate this effect in nano-grained BaTiO3 films. Based on an enhanced metastable cation solubility with Ba/Ti-ratios of 0.8 to 1.06, a significant shift of the phase transition temperature is discovered. The transition temperature increases linearly from 212 K to 350 K with increasing Ba/Ti ratio. For all Ba/Ti ratios, a completely diffused phase transition is present resulting in a negligible temperature sensitivity of the dielectric constant. Schottky defects are identified as the driving force behind the off-stoichiometry and the shift of the phase transition temperature as they locally induce lattice strain. Complementary temperature dependent Raman experiments reveal the presence of the hexagonal polymorph in addition to the perovskite phase in all cases. Interestingly, the hexagonal BaTiO3 influences the structural transformation on the Ba-rich side, while on the Ti-rich side no changes for the hexagonal polymorph at the ferroelectric transition temperature are observed. This concerted structural change of both polymorphs on the Ba-rich side causes a broad phase transition region spanning over a wide range up to 420 K including the transition temperature of 350 K obtained from dielectric measurements. These findings are promising for fine adjustment of the phase transition temperature and low temperature coefficient of permittivity.

Study of the lithium diffusion properties and high rate performance of TiNb6O17 as an anode in lithium secondary battery

TiNb6O17 and TiNb2O7 were synthesized using a solid-state method. The techniques were used to assess the electrochemical performance and lithium diffusion kinetics of TiNb6O17 related to the unit cell volume with TiNb2O7. The charge-discharge curves and cyclic voltammetry revealed TiNb6O17 to have a similar redox potential to TiNb2O7 as well as a high discharge capacity. The rate performance of TiNb6O17 was measured using a rate capability test. SSCV and EIS showed that TiNb6O17 had higher lithium diffusion coefficients during the charging. From GITT, the lithium diffusion coefficients at the phase transition region showed the largest increase from TiNb2O7 to TiNb6O17.

Ferroelastic behavior across the orthorhombic-to-tetragonal phase transition region of NKN-based lead-free ferroelectrics

In this study, the macroscopic mechanical behavior was characterized as a function of temperature (−150 °C to 400 °C) for polycrystalline (Na0.5K0.5)NbO3 with three dopant concentrations. Dopants can improve certain electromechanical properties and, in the case of NKN and Li+, shift the orthorhombic-to-tetragonal phase transition temperature to lower temperatures. In this study, the mechanical behavior of undoped NKN, LNKN6 with 6 mol. % Li+, and LNKN6 with additional dopants was characterized and compared with the temperature dependent dielectric response and crystal structure. During mechanical loading, the samples showed a nonlinear hysteretic response. At low temperatures, this is understood to be due to ferroelasticity. At temperatures in the vicinity of the orthorhombic-tetragonal phase transition temperature, a closed hysteresis behavior was observed, corresponding to a local maximum of the critical ferroelastic stress and a minimum in the remanent strain. The observed closed hysteresis behavior is suggested to be due to a stress-induced structural phase transformation.

Large electrocaloric efficiency over a broad temperature span in lead-free BaTiO3-based ceramics near room temperature

We report a large electrocaloric efficiency of 0.029 K cm kV−1 at 303 K and in a wide operating temperature range of 293 K to 313 K in a lead-free Ba0.9Sr0.1(Ti0.9Zr0.1)0.95Sn0.05O3 ceramic by using direct electrocaloric effect (ECE) measurements. Sn4+ doping in Ba0.9Sr0.1Ti0.9Zr0.1O3 not only tunes the rhombohedral-to-paraelectric phase transition temperature to room temperature but also slightly widens the phase transition region, by slightly strengthening the diffuse character and maintaining its good ferroelectricity. Also, polar nanoregions embedded in the matrix facilitate polarization rotation because of a flat energy landscape associated with the relaxor-to-ferroelectric phase transition, inducing enhanced entropy changes and consequently excellent ECE performance.