Showing papers on "Transition temperature published in 2005"
TL;DR: It is shown that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar, and above this pressure it is no longer possible to discern the characteristic feature of the FS transition.
Abstract: By confining water in nanopores of silica glass, we can bypass the crystallization and study the pressure effect on the dynamical behavior in deeply supercooled state using neutron scattering. We observe a clear evidence of a cusplike fragile-to-strong (FS) dynamic transition. Here we show that the transition temperature decreases steadily with an increasing pressure, until it intersects the homogenous nucleation temperature line of bulk water at a pressure of 1600 bar. Above this pressure, it is no longer possible to discern the characteristic feature of the FS transition. Identification of this end point with the possible second critical point is discussed.
441 citations
TL;DR: In this paper, the presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy, showing no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior).
Abstract: With the purpose of fabricating ceramics where ferroelectric and magnetic order coexist, ceramics of Pb(Fe1∕2Nb1∕2)O3 have been prepared using the traditional ceramic method following three different routes. The first is a direct via starting from oxide reagents and the other two use different kinds of FeNbO4 precursors with either monoclinic or orthorhombic structures. Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. The presence of Fe2+, detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy. The samples showed no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition (nonrelaxor behavior). Differences in the degree of diffuseness, densities and grain size were observed depending on the kind of precursor. Measurements of dc and ac electrical resistivity, dielectric constant an...
229 citations
HGST1
TL;DR: In this paper, the temperature and field hysteresis of the magnetization in the first order antiferromagnetic to ferromagnetic phase transition in FeRh films grown onto $c$-axis sapphire and MgO (001) are investigated.
Abstract: The temperature and field hysteresis of the magnetization in the first order antiferromagnetic to ferromagnetic phase transition in FeRh films grown onto $c$-axis sapphire and MgO (001) are investigated. The transition to the ferromagnetic state upon heating and antiferromagnetic state upon cooling is generally broad indicating a heterogeneous transition due to defects so that antiferromagnetic and ferromagnetic domains coexist during the transition. However, the nucleation of antiferromagnetic domains upon cooling is abrupt for FeRh on $c$-axis sapphire which is indicative of homogeneous nucleation and growth of antiferromagnetic domains. The transition is further broadened when measuring with fields applied out of plane of the sample due to internal demagnetization fields. Temperature dependent remanent magnetization measurements reveal that field induced magnetization changes are irreversible during heating, but reversible during cooling. The field dependence of the shift in transition temperature is qualitatively modeled with an Ising spin type model utilizing a mean field approach. From this calculation a shift of $\ensuremath{-}10\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{T}$ in transition temperature is determined in good agreement with the experimentally observed shift of $\ensuremath{-}8$ and $\ensuremath{-}9\phantom{\rule{0.3em}{0ex}}\mathrm{K}∕\mathrm{T}$ for FeRh films grown onto MgO (001) and c-axis sapphire, respectively.
228 citations
TL;DR: In this paper, a series of glass ceramics have been synthesized to produce bulk materials with nanometer-sized barium titanate (Ba-TiO3) crystals grown in a residue glass matrix.
Abstract: A series of glass ceramics have been synthesized to produce bulk materials with nanometer-sized barium titanate (Ba-TiO3) crystals grown in a residue glass matrix. Structure-property relations have been made to determine the size distribution and the dielectric temperature dependence of the ceramics. Through dielectric and density mixing laws, it has been inferred that depolarization fields limit the dielectric polarizability of the particles and influence the transition temperature. The transition temperature, dielectric anomaly broadening, and peak dielectric constant all scale systematically with the mean size of the BaTi03 crystals, which is consistent with an intrinsic size effect. In addition, scaling the transition temperature with the Ishikawa relation predicts a critical size of 17 nm, for which BaTiO 3 cannot support a ferroelectric transition. These results are discussed in relation to other size studies on ferroelectric materials.
216 citations
TL;DR: The electrostatic equations are coupled with those obtained by minimizing the Ginzburg-Landau functional to calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength Lambda and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layersuperlattices.
Abstract: We investigate the ferroelectric phase transition and domain formation in a periodic superlattice consisting of alternate ferroelectric (FE) and paraelectric (PE) layers of nanometric thickness. We find that the polarization domains formed in the different FE layers can interact with each other via the PE layers. By coupling the electrostatic equations with those obtained by minimizing the Ginzburg-Landau functional, we calculate the critical temperature of transition Tc as a function of the FE/PE superlattice wavelength Lambda and quantitatively explain the recent experimental observation of a thickness dependence of the ferroelectric transition temperature in KTaO3/KNbO3 strained-layer superlattices.
158 citations
TL;DR: The observed large deuteration effect cannot be elucidated by the geometric change of the hydrogen bond, which has been considered as the possible mechanism of ferroelectricity in the conventional hydrogen-bonded with double-well potential.
Abstract: Ferroelectricity and large dielectric constant at room temperature have been demonstrated for cocrystals of phenazine and anilic acids constructing supramolecular assemblies. Deuteration of the anilic acids gives rise to an increase by more than 50 K in the transition temperature, which exceeds room temperature for the deuterated chloranilic acid. At room temperature in air, the crystals show a clear polarization hysteresis with a small coercive field. Application of hydrostatic pressure and halogen substitution in the anilic acids bring about the structural effect on the transition temperature in a parallel way, whereas the deuterium substitution does this in a distinct way. The observed large deuteration effect cannot be elucidated by the geometric change of the hydrogen bond, which has been considered as the possible mechanism of ferroelectricity in the conventional hydrogen-bonded with double-well potential.
134 citations
TL;DR: In this paper, the second moment correlation length at the Kosterlitz-Thouless phase transition has been derived for the plane rotator model with a single-cluster algorithm on square lattices of a linear size up to 2048.
Abstract: We study the classical XY (plane rotator) model at the Kosterlitz–Thouless phase transition. We simulate the model using the single-cluster algorithm on square lattices of a linear size up to L = 2048. We derive the finite-size behaviour of the second moment correlation length over the lattice size ξ2nd/L at the transition temperature. This new prediction and the analogous one for the helicity modulus are confronted with our Monte Carlo data. This way βKT = 1.1199 is confirmed as inverse transition temperature. Finally, we address the puzzle of logarithmic corrections of the magnetic susceptibility χ at the transition temperature.
133 citations
TL;DR: The structure of thin films cast from regenerated solutions of Bombyx mori cocoon silk in hexafluoroisopropyl alcohol (HFIP) was studied by synchrotron X-ray diffraction during heating as discussed by the authors.
111 citations
TL;DR: The effects on dielaidoylphosphatidylethanolamine (DEPE) bilayers of ceramides containing different N-acyl chains have been studied by differential scanning calorimetry small angle x-ray diffraction and (31)P-NMR spectroscopy.
105 citations
TL;DR: Two separate liquid-solid phase transitions are detected in the two monolayers of a mica-supported phospholipid bilayer by atomic force microscopy and the variation of the width of the interfacial zone with temperature is consistent with mean-field theory.
Abstract: Two separate liquid-solid phase transitions are detected in the two monolayers of a mica-supported phospholipid bilayer by atomic force microscopy. The phase transitions of the two monolayers are decoupled by the stronger interaction between the lipid headgroups of the proximal monolayer and the mica support. The transition temperature of the proximal monolayer is increased and this transition occurs over a narrower temperature range. Both transitions occur via grain-boundary melting and the variation of the width of the interfacial zone with temperature is consistent with mean-field theory.
101 citations
TL;DR: A new non-Gaussian parameter is defined whose maximum occurs approximately at the time at which the two peaks in the probability distribution of the logarithm of displacements are most evident, approaching the commonly reported mode-coupling temperature.
Abstract: We examine the relaxation of the Kob-Andersen Lennard-Jones binary mixture using Brownian dynamics computer simulations. We find that in accordance with mode-coupling theory the self-diffusion coefficient and the relaxation time show power-law dependence on temperature. However, different mode-coupling temperatures and power laws can be obtained from the simulation data depending on the range of temperatures chosen for the power-law fits. The temperature that is commonly reported as this system's mode-coupling transition temperature, in addition to being obtained from a power law fit, is a crossover temperature at which there is a change in the dynamics from the high-temperature homogeneous, diffusive relaxation to a heterogeneous, hopping-like motion. The hopping-like motion is evident in the probability distributions of the logarithm of single-particle displacements: approaching the commonly reported mode-coupling temperature these distributions start exhibiting two peaks. Notably, the temperature at which the hopping-like motion appears for the smaller particles is slightly higher than that at which the hopping-like motion appears for the larger ones. We define and calculate a new non-Gaussian parameter whose maximum occurs approximately at the time at which the two peaks in the probability distribution of the logarithm of displacements are most evident.
TL;DR: The crystalline morphology observed in samples crystallized after nucleation in the glassy state is qualitatively different from that of samples nucleated above the glass transition temperature, and the number of crystals seems to be much greater than what could be expected from the crystallization kinetics.
TL;DR: In this paper, the authors reported detailed dielectric studies carried out on barium strontium titanate (BST) (80:20) and (60:40) compositions.
TL;DR: In this article, a multiferroic BiMnO3 with a highly distorted perovskite structure induced by the stereochemically active 6s2 electron lone pairs of Bi3+ was synthesized at a high pressure of 6 GPa.
Abstract: Multiferroic BiMnO3 with a highly distorted perovskite structure induced by the stereochemically active 6s2 electron lone pairs of Bi3+ was synthesized at a high pressure of 6 GPa. Magnetization, differential scanning calorimetry, dielectric permittivity, and in situ powder x-ray diffraction as a function of temperature were carried out, respectively. In light of comprehensive evaluation, we can conclude that the synthetic BiMnO3 ceramic displays ferromagnetic and ferroelectric orderings simultaneously, i.e., ferroelectromagnetism below its ferromagnetic Curie temperature TM∼100K.
TL;DR: In this paper, transport and magnetic properties have been studied in two sets of sol-gel prepared Pr1∕2Sr1 ∕2MnO3 nanoparticles having an average particle size of 30 and 45nm.
Abstract: Transport and magnetic properties have been studied in two sets of sol-gel prepared Pr1∕2Sr1∕2MnO3 nanoparticles having an average particle size of 30 and 45nm. Our measurements suggest that the formation of a charge-ordered state is largely affected due to lowering of the particle size, but the ferromagnetic transition temperature (TC) remains unaffected.
TL;DR: In this article, the optimal sintering temperatures are highly dependent on the chemical composition, and therefore identical annealing temperatures do not warrant similar relative densities, whereas just below the transition, in most cases the stabilization of the cubic phase increases conductivity.
Abstract: Attrition and ball milling are used as mechanical means to reduce grain size of optimized fast oxide-ion conductors La2−xRxMo2−yWyO9 (R: rare earths). Dilatometry is used to determine the optimal sintering conditions in order to obtain high density samples (greater than 96% of relative density) with help of scanning electron microscopy to characterize their microstructure. The optimal sintering temperatures are highly dependent on the chemical composition, and therefore identical annealing temperatures do not warrant similar relative densities. Complex impedance spectroscopy show that above the transition temperature of La2Mo2O9 at 580 °C, the conductivity of all the studied compounds is lower than that of the parent compound, whereas just below the transition, in most cases the stabilization of the cubic phase increases conductivity. An interesting result is that tungsten substitution, which stabilizes La2Mo2O9 against reduction, does not affect significantly the oxide ion conduction.
TL;DR: In this article, temperature dependences of the Hall coefficient, Hall mobility and thermoelectric properties of Ni-doped CoSb 3 have been characterized over the temperature range from 20 to 773 K.
TL;DR: In this article, the electrical resistivity values for these samples were measured in the temperature range from 300 up to 900 K and showed that the doping of the phase CaMnO3 with cerium induces simultaneously a marked decrease in the electrical resistance and a metal-to-insulator transition.
Abstract: Study of the perovskite-type manganites Ca1-xCexMnO3 (0.00 ≤ x ≤ 0.25) has been carried out. The electrical resistivity values for these samples were measured in the temperature range from 300 up to 900 K and show that the doping of the phase CaMnO3 with cerium induces simultaneously a marked decrease in the electrical resistivity and a metal-to-insulator transition. This behavior is exceptional since such a transition has not been observed to date in these compounds for these experimental conditions and can be attributed to the formation of Mn3+ ions as a result of charge compensation. The values of metal-to-insulator transition temperature, TMI, change with Mn3+ amount. Further the carrier doping tends to suppress the semiconductor behavior of CaMnO3 and the TMI is attributed to charge ordering observed in these compounds around 255 K.
TL;DR: Vanadium dioxide films for optical switching applications were prepared on Si 3 N 4 -film-coated silica substrates by ion beam sputtering from a vanadium metal target in an atmosphere of argon and oxygen and subsequent heat treatment as mentioned in this paper.
TL;DR: In this article, the authors investigated the properties of a series of monovalent (K) doped La 1− x K x MnO 3 polycrystalline pellets prepared by pyrophoric method.
TL;DR: In this paper, the volume transition and structure changes of the microgel particles as a function of temperature are probed using laser light scattering and small angle neutron scattering (SANS) with the objective of determining the small particle internal structure and particle-particle interactions.
Abstract: Monodispersed poly(N-isopropylacrylamide) (PNIPAM) nanoparticles, with hydrodynamic radius less than 50 nm at room temperature, have been synthesized in the presence of a large amount of emulsifiers. These microgel particles undergo a swollen- collapsed volume transition in an aqueous solution when the temperature is raised to around 34 °C. The volume transition and structure changes of the microgel particles as a function of temperature are probed using laser light scattering and small angle neutron scattering (SANS) with the objective of determining the small particle internal structure and particle-particle interactions. Apart from random fluctuations in the crosslinker density below the transition temperature, we find that, within the resolution of the experiments, these particles have a uniform radial crosslinker density on either side of the transition temperature. This result is in contrast to previous reports on the heterogeneous structures of larger PNIPAM microgel particles, but in good agreement with recent reports based on computer simulations of smaller micro- gels. The particle interactions change across the transition temperature. At tempera- tures below the transition, the interactions are described by a repulsive interaction far larger than that expected for a hard sphere contact potential. Above the volume transition temperature, the potential is best described by a small, attractive interac- tion. Comparison of the osmotic second virial coefficient from static laser light scatter- ing at low concentrations with similar values determined from SANS at 250-time greater concentration suggests a strong concentration dependence of the interaction potential. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 849 - 860, 2005
TL;DR: In this paper, a series of Ni2+xMn1xGa alloys were prepared with x=0, 0.04, 0.,06, 0,10, 0.18, and 0.24 to systematically study the effect of substitution on the martensitic and ferromagnetic transitions.
Abstract: We present the measurements of electrical resistivity , specific heat CP, Seebeck coefficient S ,a s well as thermal conductivity of the Heusler compounds Ni2+xMn1xGa from 10 to 400 K. A series of Ni2+xMn1xGa alloys were prepared with x=0, 0.04, 0.06, 0.10, 0.14, 0.18, and 0.24 to systematically study the effect of substitution on the martensitic and ferromagnetic transitions. Unusual sharp peaks were observed in both S and around the martensitic transition temperature TM, while a noticeable change of slope was seen in S and at the ferromagnetic transition temperature TC in Ni2+xMn1xGa with x0.14. For x0.14 the structural and magnetic phase transitions were found to merge together, as noticed from the sharp changes in all measured physical quantities. Existence of premartensitic transition TP was unambiguously resolved in the stoichiometric compound Ni2MnGa by the CP measurement, although such a feature becomes less pronounced with increasing x and completely disappears for the compositions x0.10. Significant thermal hysteresis loops between heating and cooling cycles appear in the vicinity of TM, which is associated with the presence of 7-layer and 5-layer modulated structures. In addition, huge peaks were observed in the thermal conductivity near TM. We connected this observation to the nesting of the Fermi-level density of states, which is appropriate for the Peierls transition.
TL;DR: The main finding is that T(C) is not proportional to n(s)(0); instead, it is found proportional to ns(1/2.3+/-0.4).
Abstract: We report measurements of the ab-plane superfluid density n(s) (magnetic penetration depth lambda) of heavily underdoped films of YBa2Cu3O6+x, with T(C)'s from 6 to 50 K. We find the characteristic length for vortex unbinding transition equal to the film thickness, suggesting strongly coupled CuO2 layers. At the lowest dopings, T(C) is as much as 5 times larger than the upper limit set by the 2D Kosterlitz-Thouless-Berezinskii transition temperature calculated for individual CuO2 bilayers. Our main finding is that T(C) is not proportional to n(s)(0); instead, we find T(C) proportional to ns(1/2.3+/-0.4). This conflicts with a popular point of view that quasi-2D thermal phase fluctuations determine the transition temperature.
TL;DR: In this paper, the authors investigated the dielectric properties of Mott insulators under magnetic fields and external quasihydrostatic pressures, and they showed that the ferroelectric transition in GdMnO3 is a first-order displacive-type one.
Abstract: We have investigated dielectric properties in Mott insulators GdMnO3 and TbMnO3 under magnetic fields and external quasihydrostatic pressures. In the case of GdMnO3, thermal hysteresis for dielectric constant e and discontinuous lattice distortion were observed at ferroelectric transition temperature (TC), and ferroelectric spontaneous polarization was suppressed by the application of external pressure. These results indicate that the ferroelectric transition in GdMnO3 is a first-order displacive-type one. On the other hand, the thermal hysteresis and discontinuous lattice striction were not observed at TC in TbMnO3. The peak of e corresponding to the ferroelectric transition was shifted toward higher temperatures by the application of external pressure in TbMnO3. The ferroelectric transition of TbMnO3 was thought to be a second-order order–disorder-type one.
TL;DR: This simulation demonstrates that the peak enhancement observed in the neutron scattering experiments below the transition temperature arises exclusively from particle exchange, illuminating the role of Bose-statistical effects on the dynamics of the quantum liquid.
Abstract: The formation of a superfluid when 4He is cooled below the characteristic lambda transition temperature is accompanied by intricate quantum mechanical phenomena, including the emergence of a Bose condensate. A combination of path integral and semiclassical techniques is used to calculate the single-particle velocity autocorrelation function across the normal-to-superfluid transition. We find that the inclusion of particle exchange alters qualitatively the shape of the correlation function below the characteristic transition temperature but has no noticeable effect on the dynamics in the normal phase. The incoherent structure factor extracted from the velocity autocorrelation function is in very good agreement with neutron scattering data, reproducing the width, height, frequency shift, and asymmetry of the curves, as well as the observed increase in peak height characteristic of the superfluid phase. Our simulation demonstrates that the peak enhancement observed in the neutron scattering experiments below the transition temperature arises exclusively from particle exchange, illuminating the role of Bose-statistical effects on the dynamics of the quantum liquid.
TL;DR: In this paper, the viscous and thermal relaxation rates of an interacting fermion gas are calculated as functions of temperature and scattering length, using a many-body scattering matrix which incorporates medium effects due to Fermi blocking of intermediate states.
Abstract: The viscous and thermal relaxation rates of an interacting fermion gas are calculated as functions of temperature and scattering length, using a many-body scattering matrix which incorporates medium effects due to Fermi blocking of intermediate states. These effects are demonstrated to be large close to the transition temperature T{sub c} to the superfluid state. For a homogeneous gas in the unitarity limit, the relaxation rates are increased by nearly an order of magnitude compared to their value obtained in the absence of medium effects due to the Cooper instability at T{sub c}. For trapped gases the corresponding ratio is found to be about three due to the averaging over the inhomogeneous density distribution. The effect of superfluidity below T{sub c} is considered to leading order in the ratio between the energy gap and the transition temperature.
TL;DR: In this paper, phase and conformational behavior of poly(N-vinylcaprolactam) was studied as a function of polymer concentration, concentration of NaCI, and concentration of sodium dodecyl sulfate (SDS).
Abstract: Phase and conformational behavior of poly(N-vinylcaprolactam) was studied as a function of polymer concentration, concentration of NaCI, and concentration of sodium dodecyl sulfate (SDS). Precise measurements of the partial heat capacity of the polymer were first carried out within the temperature range 10-125 °C. Thermodynamic parameters of the phase separation transition (transition temperature, enthalpy, and heat capacity increment) do not change with variations in polymer concentration. In the presence of salt the transition temperature decreases, the enthalpy increases, and the heat capacity increment does not vary significantly. Beginning with the SDS concentration of 0.005 M, the phase separation is suppressed and the heat capacity peak splits into two peaks. Upon further increase in surfactant concentration the amplitude of the low-temperature peak increases while that of the high-temperature peak vanishes. Phase separation transition in aqueous solutions of N-vinylcaprolactam-methacrylic acid copolymers of different compositions were studied at different polymer concentrations and pH (4-12). The transition parameters do not depend on polymer concentration and pH.
TL;DR: Magnetic entropy change above 300 K was observed in a Cu-doped manganites of La 0.7Sr0.3Mn1−xCuxO3 (x = 0.05, 0.1 ).
TL;DR: In this article, the effect of applied mechanical strains on the ferroelectric and dielectric properties of a model single crystal is investigated using a phase field model based on the time-dependent Ginzburg-Landau equation.