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Showing papers on "Phase transition published in 1969"


Journal ArticleDOI
TL;DR: In this paper, Monte Carlo computations have been performed in order to determine the phase transitions of a system of particles interacting through a Lennard-Jones potential, and an indirect determination of the phase transition of the hard-sphere gas is made which is essentially in agreement with the results of more direct calculations.
Abstract: Monte Carlo computations have been performed in order to determine the phase transitions of a system of particles interacting through a Lennard-Jones potential. The fluid-solid transition has been investigated using a method recently introduced by Hoover and Ree. For the liquid-gas transition a method has been devised which forces the system to remain always homogeneous. A comparison is made with experiment in the case of argon. An indirect determination of the phase transition of the hard-sphere gas is made which is essentially in agreement with the results of the more direct calculations.

1,101 citations


Journal ArticleDOI
TL;DR: In this paper, a simple model for a semiconductor-metal transition, based on the existence of both localized (ionic) and band (Bloch) states, was proposed, which differs from other theories in that we assume the one-electron states to be essentially unchanged by the transition.
Abstract: We propose a simple model for a semiconductor-metal transition, based on the existence of both localized (ionic) and band (Bloch) states. It differs from other theories in that we assume the one-electron states to be essentially unchanged by the transition. The electron-hole interaction is responsible for the anomalous temperature dependence of the number of conduction electrons. For interactions larger than a critical value, a first-order semiconductor-metal phase transition takes place.

701 citations


Journal ArticleDOI
TL;DR: In this article, the usual static scaling laws are generalized to nonequilibrium phenomena by making assumptions on the behavior of time-dependent correlation functions near the critical point of second-order phase transitions.
Abstract: The usual static scaling laws are generalized to nonequilibrium phenomena by making assumptions on the behavior of time-dependent correlation functions near the critical point of second-order phase transitions. At any temperature different from ${T}_{c}$, the correlation functions are assumed to reflect the hydrodynamic behavior of the system, for sufficiently long wavelengths and low frequencies. As the critical temperature is approached, however, the range of spatial correlations in the system diverges, and the domain of applicability of hydrodynamics is reduced to a vanishingly small region of wavelengths and frequencies. The dynamic-scaling assumptions lead to predictions for the behavior of the hydrodynamic parameters near ${T}_{c}$, as well as for the form of the correlation functions for macroscopic distances and times, outside the hydrodynamic range. In particular, singularities are predicted to occur in the temperature dependence of transport coefficients, and anomalies are expected in the frequency spectrum of certain operators, which are observable by inelastic scattering of neutrons or light. A distinction is made between the restricted dynamic-scaling hypothesis, which refers to the order parameter only, and extended dynamic scaling, which applies to other operators and involves stronger assumptions. Applications are discussed to antiferromagnets, ferromagnets, the gas-liquid critical point, and the $\ensuremath{\lambda}$ transition in superfluid helium. Specific experiments are suggested to test the scaling assumptions, and existing experimental evidence is briefly reviewed. Finally, a comparison is made with other theories of dynamical behavior near critical points.

501 citations


Journal ArticleDOI
TL;DR: In this paper, the Gibbs state in the infinite volume limit is shown to exist as a primary state of a UHF algebra and the expectation value of any local observables in the state as well as the mean free energy depend analytically on the potential.
Abstract: A one dimensional infinite quantum spin lattice with a finite range interaction is studied. The Gibbs state in the infinite volume limit is shown to exist as a primary state of a UHF algebra. The expectation value of any local observables in the state as well as the mean free energy depend analytically on the potential, showing no phase transition. The Gibbs state is an extremal KMS state.

243 citations


Journal ArticleDOI
TL;DR: In this article, scaling laws for anisotropic magnetic systems are stated, where the anisotropy parameters are either scaled or held fixed, and the critical behavior of thermodynamic quantities in the system is determined.
Abstract: Scaling laws are stated for anisotropic magnetic systems, where the anisotropy parameters are either scaled or held fixed. Combining the two ways of scaling, the critical behavior of thermodynamic quantities in anisotropic systems is determined. Particular attention is drawn to the temperature range where the anisotropy becomes important, and to the dependence there of the different quantities on the anisotropy parameters. In a transverse magnetic field the phase transition of an anisotropic magnet takes place along aλ-line. Assuming the singular part of the free enthalpy to depend on the distance from theλ-line, anomalous corrections to the transverse susceptibility and magnetization are calculated. For an experimental verification of many of the results, experiments including a variation of the anisotropy parameters or a finite transverse field are necessary.

151 citations


Journal ArticleDOI
TL;DR: In this paper, the temperature of the α-β transition is raised 10.6±0.4°C/kb by uniaxial compression perpendicular and parallel to the optic axis at a confining pressure of 3 kb.
Abstract: Experiments on oriented cores from a single crystal of quartz show that the temperature of the α-β transition is raised 10.6±0.4°C/kb and 5.0±0.4°C/kb by uniaxial compression perpendicular and parallel, respectively, to the optic axis at a confining pressure of 3 kb. Approximately the same results are indicated for confining pressures ranging from 1 to 5 kb. There is no detectable curvature of the phase boundary for uniaxial stresses σ between 0 and 10 kb: |(d2Tα-β/dσ2)| < 0.05°C/kb2. The increase of transition temperature with hydrostatic pressure of 25.8±0.3°C/kb between 1 and 5 kb also determined in these experiments is consistent with previous determinations. These results and others for quartz are analyzed assuming the α-β inversion is either a λ transition or a first-order transition characterized by a small reversible transformation strain. Although both hypotheses are roughly consistent with most of the results, the hysteresis in the transition suggests that the second may be preferable, and a theory is developed that describes the effect of general nonhydrostatic stress on such transitions.

147 citations


Journal ArticleDOI
TL;DR: In this paper, the Fulde-Ferrel model was used to investigate the properties of the phase transitions from superconducting states to the other states, where the phase transition from a superconductor to a non-superconductor was studied.
Abstract: The Fulde-Ferrel model, in which a molecular field is acting on the spins of the con­ duction electrons responsible for supercond,uctivity, is investigated. The superconducting state, that is described by the condensate wave function oscillating in space and gives rise to a gapless energy spectrum, is shown to be the ground or equilibrium state for some values of the pairing interaction and the molecular field. Thermodynamic properties of such gapless superconducting. states are investigated extensively. Special attention is paid on the properties of the phase transitions from such superconducting states to the other states.

125 citations


Journal ArticleDOI
TL;DR: In this paper, Neutron inelastic scattering methods are used to demonstrate the close connection between the antiferroelectric phase transition at 110°K in SrTiO 3 and the temperature dependence of the triply degenerate Γ 25 mode of vibration of wave vector.

124 citations



Journal ArticleDOI
TL;DR: In this paper, experimental evidence is presented bearing on the low current conduction and on the rapid electrical switching phenomena that have been found in thin films of certain amorphous chalcogenide semiconducting materials.
Abstract: : Experimental evidence is presented bearing on the low current conduction and on the rapid electrical switching phenomena that have been found in thin films of certain amorphous chalcogenide semiconducting materials. The principal findings are that (1) the low current conduction consists of an 'ohmic' region linear with voltage and an exponentially varying nonlinear region, both of which arise from the same conduction process; (2) at voltages just below switching, the equivalent parallel capacitance of the film becomes negative; and (3) a field-influenced dielectric phase transition is implicated in the switching process. The phase transition temperature appears to be related to the glass transition temperature. (Author)

111 citations


Journal ArticleDOI
TL;DR: In this paper, the external optical phonon modes in the ammonium and deuteroammonium halides have been studied through their intrinsic phase transitions in the temperature range 4 −290°K using infrared and Raman techniques.
Abstract: The external optical phonon modes in the ammonium and deuteroammonium halides have been studied through their intrinsic phase transitions in the temperature range 4–290°K using infrared and Raman techniques. The number of infrared and Raman active modes are in agreement with group theoretical predictions for the phases II, III, and IV, with the exception that no measurable anisotropic splitting of the out‐of‐phase mode in the tetragonal phase was observed in the infrared spectra. Whilst the frequency of the infrared reststrahlen modes showed only small discontinuities with temperature as the phase transitions were traversed, the phonon lifetimes of these modes showed distinct increases as the temperature was lowered through each phase transition. Estimates of the intrinsic ionic distortion present in NH4Cl and NH4Br are given. The compressibilities of NH4Cl and NH4Br at 4°K are calculated to be 3.86 × 10−12 and 6.79 × 10−12 cm2 dyn−1.

Journal ArticleDOI
TL;DR: In this article, low-angle X-ray diffraction has been used to characterize the two lyotropic mesomorphic phases (neat phase and middle phase) which are formed in the dodecylhexaoxyethylene glycol monoether + water system.
Abstract: Low-angle X-ray diffraction has been used to characterize the two lyotropic mesomorphic phases (neat phase and middle phase) which are formed in the dodecylhexaoxyethylene glycol monoether + water system. The occurrence of these two anisotropic mesomorphic phases does not affect the behaviour of the thermodynamic excess functions which have been interpreted in terms of solute-water interactions. Careful measurements of water vapour pressure have been necessary to establish the limited extent of the two phase co-existence regions which separate homogeneous mesomorphic phase regions from isotropic solution in this system. Volume and heat capacity measurements as a function of temperature across mesomorphic phase boundaries have confirmed that the neat phase/isotropic solution and the middle phase/isotropic solution transformations are first-order phase transitions with very small volume and enthalpy changes.

Journal ArticleDOI
TL;DR: In this paper, the untwisting and alignment of high-pitch cholesteric liquid crystals, mixtures of para-azoxyanisole and cholesteryl esters, were observed along an applied magnetic field.
Abstract: We optically observe the untwisting and alignment, along an applied magnetic field, of high-pitch cholesteric liquid crystals, mixtures of para-azoxyanisole and cholesteryl esters. The results agree quantitatively with de Gennes's predictions and allow a determination of the twist elastic constant of pure para-azoxyanisole.

Journal ArticleDOI
TL;DR: In this article, phase transitions were observed in a number of crystalline 1:1 TCNQ ion-radical salts by absolute paramagnetic susceptibility and electrical conductivity measurements over a wide temperature range.


Journal ArticleDOI
TL;DR: In this paper, the thermodynamics of single superparamagnetic particles are studied by means of a Monte Carlo technique which was recently derived for the calculation of compact ferromagnets, and an exact (numerical) calculation of the magnetization and of the internal energy of the particle is obtained.

Journal ArticleDOI
TL;DR: In this paper, the authors measured the T1 of the proton spin-lattice relaxation times as a function of temperature for KBH4 and LiBH4, and found that the magnetization recovery is approximately exponential.
Abstract: Proton spin–lattice relaxation times, T1, have been measured as a function of temperature for KBH4, NaBH4, and LiBH4. For NaBH4 and KBH4, 23Na and 11B relaxation measurements were also made. In all cases, the magnetization recovery is approximately exponential. Correlation times, τc, derived from the T1 data were used to calculate activation energies, V, for BH4− ion reorientations. For the cubic phase of KBH4, V = 14.8 ± 0.4 kJ/mole (3.55 ± 0.1 kcal/mole) (± always refers to rms error) from measurements on proton and 11B. For NaBH4, V was found to be 11.2 ± 0.5 and 14.8 ± 0.7 kJ/mole (2.7 ± 0.1 and 3.5 ± 0.2 kcal/mole) for the high‐ (cubic) and low‐temperature (tetragonal) phases; an anomaly in τc was observed at temperatures slightly below the phase transition, and may be interpreted as a relatively sudden change in V associated with the phase transition. In LiBH4, a rather broad minimum was observed for the proton T1 vs temperature; this has been interpreted as due to two inequivalent BH4− tetrahedra w...

Journal ArticleDOI
TL;DR: The correlation of the atomic displacements in KNbO 3 and BaTiO 3 explains the small entropy change between the ferroelectric tetragonal and the paraelectric cubic phase as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this paper, the following lattice systems were shown to exhibit phase transitions if the temperature is sufficiently low and the transverse (or kinetic) part of the interaction is sufficiently small.
Abstract: We prove that the following lattice systems: (1) anisotropic Heisenberg model, (2) Ising model with transverse magnetic field, (3) quantum lattice gas with hard cores extending over nearest neighbours, exhibit phase transitions if the temperature is sufficiently low and the transverse (or kinetic) part of the interaction sufficiently small.

Journal ArticleDOI
TL;DR: In this article, it was shown that if the interaction range or strength in units of kT is of O(log N ) or O( log N) 1 4, then the two dimensional Bose gas will condense at temperatures O( T 0 log N ), where T 0 is the condensation temperature in three dimensions.

Journal ArticleDOI
TL;DR: A brief review of the current state of knowledge concerning quasi-two-dimensional Heisenberg ferromagnets and antiferromagnetic systems can be found in this paper, where a comparison is made with typical three-dimensional magnetic systems.
Abstract: A brief review is presented of the present state of knowledge (both theoretical and experimental) concerning quasi‐two‐dimensional Heisenberg ferromagnets and antiferromagnets, and comparisons are made with typical three‐dimensional magnetic systems The greatly enhanced quantum and short‐range order effects in two dimensions expose the limitations of most current statistical theories and should stimulate both theoretical and experimental interest in a number of directions These include zero‐point spin deviations (for antiferromagnets), bound‐magnon states, possible new phase transitions to disordered states with infinite susceptibility, critical coefficients, the role of anisotropy in stabilizing long‐range order in two dimensions, and the study of propagating spinwaves in the paramagnetic phase



Journal ArticleDOI
M. E. Lines1
TL;DR: In this paper, a statistical approximation for displacement ferroelectrics is developed, which enables dielectric properties to be described directly in terms of a limited number of microscopic parameters, such as polarization, soft-mode frequency, static and dynamic susceptibilities, all as functions of temperature both close to and away from the Curie point.
Abstract: A statistical approximation is developed for displacement ferroelectrics which enables dielectric properties to be described directly in terms of a limited number of microscopic parameters. In particular, for systems with only one grossly temperature-dependent optic mode of lattice vibration, the number of parameters is sufficiently few that they can be overdetermined by a direct comparison of theory with dielectric properties alone. These microscopic parameters are very much more closely connected with the fundamental microscopic forces in the system than are the more familiar macroscopic (thermodynamic) parameters. For a single-soft-mode system, many dielectric properties are calculated quantitatively in terms of the microscopic parameters. These properties include polarization, soft-mode frequency, static and dynamic susceptibilities, all as functions of temperature both close to and away from the Curie point. Sections discussing the order of the phase transition and some nonlinear properties of the polar phase are also presented. In parts II and III of the present series of papers the method is extended and used to discuss in detail the dielectric properties of lithium tantalate.

Journal ArticleDOI
TL;DR: In this article, the high-temperature phase change in tetragonal RbH2PO4 at 86°C was found to result in a quasi-irreversible transition to a monoclinic modification which seems to be isomorphous with monOClinic RbD2PPO4 and KD2PO4 and was accompanied by a distortion of the PO4 groups and an ordering of the protons.
Abstract: The high‐temperature phase change in tetragonal RbH2PO4 at 86°C is found to result in a quasi‐irreversible transition to a monoclinic modification which seems to be isomorphous with monoclinic RbD2PO4 and KD2PO4. The transition is accompanied by a distortion of the PO4 groups and an ordering of the protons. From the analogy with monoclinic KD2PO4 it seems probable that the protons attach to one upper and one lower corner of a PO4 group giving rise to pyroelectric behavior along the b axis. The similarity of the infrared spectra of the high‐temperature forms of RbH2PO4 and KH2PO4 demonstrates that the above statements are valid for KH2PO4 as well.

Journal ArticleDOI
TL;DR: In this paper, the authors used differential thermal analysis and X-ray powder diffraction studies to determine the temperatures of phase transitions in each of these compounds, and observed a phase transition in CdSiP2 at 1098° C some 22° C below the melting point.
Abstract: ZnSnP2, ZnGeP2, ZnSiP2, CdGeP2 and CdSiP2 have been prepared in single or polycrystalline form by direct synthesis from the elements, combination of the group IV element with the II-V2 phosphide, vapour transport or solution growth. Differential thermal analysis and X-ray powder diffraction studies have been used to determine the temperatures of phase transitions in each of these compounds. Of particular interest is the observation of a phase transition in CdSiP2 at 1098° C some 22° C below the melting point. The thermal analysis studies of ZnSnP2 indicate a peak, the cause of which is uncertain, at 720° C which is well separated from the melting temperature of 930° C; further ZnSnP2 does not appear to be congruently melting and has a freezing point at 970° C. c/a ratios have been determined for all five compounds to 1 part in 2000.

Journal ArticleDOI
TL;DR: In this article, the electrical conductivity and demagnetization of iron have been measured at pressures up to 370 kbar, and the experimental results provide confirmation that the high-pressure ϵ-phase of iron is non-magnetic.

Journal ArticleDOI
TL;DR: The phase boundary between the antiferromagnetic and the spin-flop phase in the H plane extends only to a maximum angle with respect to the easy axis of order (anisotropy energy/exchange energy), where it ends in critical points as mentioned in this paper.
Abstract: We have studied the transitions induced by fields of arbitrary direction between the antiferromagnetic, the spin‐flop, and the paramagnetic phase of a two‐sublattice uniaxial antiferromagnet at zero temperature in molecular‐field approximation. We find that the phase boundary between the antiferromagnetic and the spin‐flop phase in the H plane extends only to a maximum angle with respect to the easy axis of order (anisotropy energy/exchange energy), where it ends in critical points. This behavior explains the sensitive angular dependence of ultrasonic absorption and magnetic resonance experiments.

Journal ArticleDOI
TL;DR: The tunneling paraconductivity of tunneling junctions has been shown to have a strong temperature dependence, tending to infinity at the transition as mentioned in this paper, and the numerical magnitude of this property is sufficiently large to be observable for junctions of very low normal resistance.
Abstract: When one metallic film of a tunneling junction is in the superconducting state but the other is above its transition temperature, fluctuations in the pair field of the second film cause instantaneous Josephson currents to flow. Application of the Kubo formula to these current fluctuations yields a conductivity with a strong temperature dependence, tending to infinity at the transition. The numerical magnitude of this "paraconductivity" is sufficiently large to be observable for junctions of very low normal resistance (and may possibly be compared with some recent measurements of Lipsonet al.). High-frequency studies would determine directly the pair relaxation rate. An experimental advantage of tunneling paraconductivity is that it is not sensitive to the electron mean free path and therefore does not require amorphous films.

Journal ArticleDOI
TL;DR: The temperature dependence of the electric field gradient (EFG) at the sodium site has been determined in the ferroelectric and paraelectric phases of NaNO 2, where the existence of the antiferroelectric phase can not be evidenced from the present study as mentioned in this paper.
Abstract: The temperature dependence of the electric field gradient (EFG) at the sodium site has been determined in the ferroelectric and paraelectric phases of sodium nitrite (NaNO 2 ). Special attentions have been paid to the narrow temperature range near the ferroelectric Curie point T c where the antiferroelectric phase had been discovered. The main results obtained are: (1) the field gradient varies linearly with the square of the long range order parameter determined by the X-ray study in the ferroelectric phase; (2) a small, but abrupt, change at T c in the field gradient fives an evidence for a phase transition of the first kind; (3) the existence of the antiferroelectric phase can not be evidenced from the present study;(4) slight anomalies exist at 168°C and 178°C in the temperature variation of the field gradient; and (5) the field gradient decreases linearly with increasing temperature in the temperature ranges between 168°C and 178°C and also between 180°C and 230°C. It has been shown that these unusua...