Sharp First-order Phase Transition Research Articles

Monte Carlo simulations of the short time dynamics of a first-order irreversible phase transition

The ZGB model (Ziff–Gulari–Barshad, Phys. Rev. Lett. 56 (1986) 2553) for the catalytic oxidation of carbon monoxide has a single parameter given by the normalized partial pressure of CO molecules ( P CO). For P CO⩾ P CO Coex≃0.52583 the surface of the catalyst becomes irreversibly covered by CO molecules and the system cannot escape from this state. However, for P CO slightly below P CO Coex the system reaches an active stationary state. So, just at P CO Coex a sharp first-order irreversible phase transition is observed. It is shown that a study of the short time dynamics of the ZGB model allows to obtain a fairly accurate evaluation of the upper spinodal point given by P CO Usp≃0.52675(5). This figure is in excellent agreement with extensive simulations performed using the constant coverage ensemble.

Heat capacity of a giant single crystal of C 60

The heat capacity of a giant single crystal of C 60 (8×6×6 mm 3) was measured from 6 to 350 K by adiabatic calorimetry. A very sharp first-order phase transition arising from the orientational ordering of C 60 molecules was observed at 262.1 K, and a glass transition due to freezing of the reorientational motion of C 60 molecules was also found at 84.6 K. The transition temperature and the height of the heat capacity peak are much higher than any other calorimetric results reported previously. The transition enthalpy and entropy are also large in comparison with the values determined hitherto for a powder sample. These facts reveal that the phase transition of C 60 is strongly affected by crystallinity as well as purity. The C 60 giant single crystal used here is supposed to be free from these effects. The present results may be considered as reference thermodynamic values and behavior for crystalline C 60.

Rotational ordering transition in single-crystal C60 studied by Raman spectroscopy.

Raman spectroscopic data are presented on the rotational ordering fcc→sc transition in single-crystal C60. Splittings and activation of new modes reveal the influence of the cubic structure, and are in agreement with the crystal symmetry in both phases. The temperature dependence of the spectra is consistent with a sharp first-order phase transition near 252 K. A simple model is proposed for the explanation of the temperature dependence of the spectra, involving a large vibrational-rotational coupling in the fcc phase, and essentially no rotational disorder in the sc phase.

Field-induced sharp ferroelectric phase transition inK0.937Li0.063TaO3

Sharp first-order ferroelectric phase transitions as indicated by sharp peaks of the dielectric permittivity arise in ${\mathrm{K}}_{0.937}$${\mathrm{Li}}^{0.063}$${\mathrm{TaO}}_{3}$ upon cooling or heating in electric fields 75lEl300 kV/m. They cancel the random dipolar fields due to frozen-in off-center ${\mathrm{Li}}_{+}$ ions, which destroy the phase transition and give rise to low-temperature domain states if E=0. Sharp zero-field transitions with a dispersionless peak of \ensuremath{\epsilon}' at ${\mathrm{T}}_{\mathrm{c}}^{+}$=104.5 K, which accurately follows the Landau-Devonshire theory at T${\mathrm{T}}_{\mathrm{c}}^{+}$, are observed after field cooling with E75 kV/m.

Nature of the deconfining phase transition in SU(3) lattice gauge theory.

Monte Carlo calculations on lattices with large spatial volume show that the SU(3) deconfining phase transition is more weakly first order than previously thought. We have studied the transition for ${N}_{T}=4 \mathrm{and} 6$ on lattices of spatial volumes ${16}^{3}$, ${20}^{3}$, and ${24}^{3}$. The ${24}^{3}$\ifmmode\times\else\texttimes\fi{}4 calculations show a sharp first-order phase transition, yielding a latent heat $\frac{\ensuremath{\Delta}\mathcal{E}}{{T}^{4}}$ of 2.54\ifmmode\pm\else\textpm\fi{}0.12. The ${24}^{3}$\ifmmode\times\else\texttimes\fi{}6 calculations suffer greater finite-volume smearing, but suggest that $\frac{\ensuremath{\Delta}\mathcal{E}}{{T}^{4}}=2.48\ifmmode\pm\else\textpm\fi{}0.24$. Correlation lengths increase significantly near the transition, and the energy plus pressure of the ordered phase depends strongly on $\ensuremath{\beta}$.

A computer simulation study of the melting and freezing properties of a system of Lennard-Jones particles

An investigation of the thermodynamic and structural properties of a system of LJ particles around the solid-liquid transition has been performed using isobaric-isothermal (NPT) moleclar dynamics computer simulation techniques. A sharp first-order phase transition is observed. However, the solid is shown to superheat considerably giving an apparent melting temperature ∼ 14 per cent too high at zero pressure. Extensive tests of the simulation run, etc., were made to separate simulation artifacts from genuine physical phenomena. We conclude that the observed superheating is a real effect resulting in a metastable state. A comparison of these results with previous computer simulation studies were made. An investigation of apparent diffusion coefficient, the isothermal compressibility, and the constant pressure specific heat was also made.

Heat capacity and phase transition of tetrahydrofuran clathrate hydrate

Heat capacity of tetrahydrofuran clathrate hydrate THF·16.81H 2O doped with KOH ( x = 1.8 × 10 −4 in the mole fraction of KOH in KOH and water) was measured in the temperature range 13–280 K. A sharp first-order phase transition having a large tail on the high temperature side was observed at 62 K and excess entropy due to the transition was determined to be 2.56JK −1 (H 2O-mol) −1. From a comparison with thermal behavior of hexagonal ice, it was indicated that this transition was related to ordering of protons in the host lattice.

First-order transition to a novel metallic state in [Na y+(CH) − y] x: In situ electron spin resonance during chemical and electrochemical doping

The onset of the temperature-independent Pauli spin susceptibility takes place in [Na y +(CH) − y ] x as a sharp first-order phase transition at a dopant concentration of approximately 6 mole%. Using either chemical or electrochemical doping techniques, a single symmetric Lorentzian ESR line was observed for the full range of doping and at all temperatures, thereby ruling out the formation of metallic islands. Although the abrupt transition is easily smeared by disorder and/or non-uniform doping, the sharp onset of Pauli susceptibility is an intrinsic feature of the ordered system. The results are interpreted in terms of a first-order phase transition (at y c ∼= 0.06) from a soliton lattice (or a highly correlated soliton liquid) to a novel metallic state in which the finite density of states arises from a lattice of polaron-like distortions with half-filled polaron sub-band in the Peierls gap.

Double ferromagnetism in single-crystal Gd-Y-Lu alloys

Magnetization, electrical resistivity, specific-heat and thermal-expansion measurements have been made on Gd-Y-Lu single crystals. Low isofield magnetization data for the $a$-axis sample of ${\mathrm{Gd}}_{75}$${\mathrm{Y}}_{17.5}$ ${\mathrm{Lu}}_{7.5}$ exhibit two different Curie-Weiss regimes, which suggests double ferromagnetism. Electrical resistivity, specific-heat, and thermal-expansion data show two anomalies at the transition temperatures. The anomaly at 231.5 K shows a $\ensuremath{\lambda}$-type second-order phase transition and the anomaly at 223 K shows a sharp spike first-order phase transition.

Statistical fluctuations in thei132model

The finite-temperature Hartree-Fock-Bogoliubov cranking equations are solved for the ${i}_{\frac{13}{2}}$ model. For any temperature below $k{T}_{c}=0.2$ MeV, rotations induce a sharp first-order phase transition. When statistical fluctuations in the pair gap $\ensuremath{\Delta}$ are included, the phase transition is smoothed out for $\frac{1}{2}{T}_{c}lTl{T}_{c}$. The rotation-aligned ${i}_{\frac{13}{2}}$ pair is unaffected by temperatures up to 0.5 MeV. The finite-temperature violation of the zero-temperature Hartree-Fock-Bogoliubov relation ${R}^{2}=R$ is given by the quasiparticle number fluctuation.

Statistical fluctuations and first-order phase transitions in heated rotating nuclei

For any temperature below 0.20 MeV, the finite-temperature Hartree-Fock-Bogoliubov cranking theory predicts a sharp first-order phase transition in the i 1 3 2 model. However when statistical fluctuations in the pair gap are included, these phase transitions are smoothed out when the temperature is as low as 0.05–0.10 MeV.

High resolution calorimeter for the investigation of melting in organic and biological materials

A high-resolution, high-sensitivity ac calorimeter has been developed to investigate the ''melting'' of organic and biological materials. The heart of this system is a simple yet very versatile sample cell which can be reused. High-temperature-resolution studies of the melting of n-octadecane and tert-butyl alcohol indicate interesting premelting and prefreezing phenomena in the specific heat capacity in these substances. With pure dipalmitoyl L-alpha-lecithin (DPL), in water, we obtain a very sharp (FWHM=0.38 degrees C) first-order phase transition showing no pretransition broadening or post-transition tails in the specific heat curves near the 41.2 degrees C transition point.