On the nature of the phase transition in MnO

The temperature dependence of the nuclear Bragg reflection (222) and of the magnetic Bragg reflection (111) of MnO was simultaneously measured by neutron diffraction on a powder sample. The intensity of the nuclear line exhibits a 40% drop at temperatures between 113 and 116 K. This dip was attributed to a decrease of the Bragg intensity due to structural fluctuations. If the effect of these fluctuations on the magnetic intensity is taken into account, the magnetization discontinuity is found to be greatly reduced or even to disappear, in disagreement with other authors.     

On the master equation with time-dependent transition probabilities

The asymptotic behaviour of solutions of the master equation with time-dependent transition probabilities by means of the Kullback information is investigated. We assume that there are no absorbing states.     

On the nature of metal-semiconductor phase transition in vanadium dioxide

The method of coercive temperature distribution function is used to prove that the metal-semiconductor temperature-induced phase transition in vanadium dioxide manifests itself as a Mott electronic transition.     

On the nature of the phase transition in the KDP systems

Using the Landau theory of phase transitions it has been shown that for a second order phase transition Ω/k_BT_c ? 0.01. and its isomorphs 4Ω/J¹ ? 1 and for a first order transition Ω/k_BT_c ? 0.01.     

On the nature of the step-like transition in the UP-USe system

Neutron diffraction experiments on the solid solution UP_0.9Se_0.1 indicate that the step-like transition occurring at low temperature in the UP-USe system is of the same nature as in UAs and UP. It corresponds to a transition from a collinear single-k structure to a non-collinear double-k structure.     

On the nature of the γ-α transition in cerium

In 1964 Davis and Adams established that the large increase of the thermal expansion and compressibility in the critical region of the γ-to α-Ce phase transition occurs predominantly in the α phase. This provides strong evidence that a tricritical point is realized in Ce. This also means that the aforementioned transition is not isomorphic and that α-Ce should have a distorted fcc structure. A careful examination of Jayaraman’s data (1965) shows that a second-order transition line continues beyond the tricritical point to the vicinity of a triple point on the melting curve. The phase boundary with the tricritical point and the minimum of the melting curve are reconstructed within the framework of Landau theory. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 111–117 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

On the nature of the magnetic transition in a Mott insulator

Using a combination of exact enumeration and the dynamical mean-field theory (DMFT) we study the drastic change of the spectral properties, obtained in the half-filled two-dimensional Hubbard model at a transition from an antiferromagnetic to a paramagnetic Mott insulator, and compare it with the results obtained using the quantum Monte Carlo method. The coherent hole (electron) quasiparticle spin-polaron subbands are gradually smeared out when the AF order disappears, either for increasing Coulomb repulsion U at fixed temperature T, or for increasing T at fixed U. Within the DMFT we present numerical evidence (a continuous disappearence of the order parameter) suggesting that the above magnetic transition is second order both in two and in three dimensions.Received: 20 November 2004, Published online: 9 April 2004PACS: 71.30. + h Metal-insulator transitions and other electronic transitions - 71.10.Fd Lattice fermion models (Hubbard model, etc.) - 79.60.-i Photoemission and photoelectron spectraThis work is dedicated to Professor Ole Krogh Andersen on the occasion of his 60th birthday.     

On the nature and the order of the deconfining transition in QCD

The determination of the parameters of the deconfining transition in N _f = 2 QCD and its relevance to the understanding of the mechanism of color confinement are discussed.     

On the nature of a new phase transition in α-MnS

Magnetic-susceptibility and X-ray-diffraction data of polycrystalline and oriented single crystal α-MnS reveal a new phase transition at T_tr = 131 K below the Néel temperature T_N = 148 K. The phase transition is characterized by an abrupt inversion of the rhombohedral distortion of the f.c.c. lattice along [111]. At T_tr there is a discontinuous change in the susceptibility of single crystals.     

On the nature of ion bombardment-induced phase transformations in films of transition metals

Abstract

Electron diffraction studies have been made of polycrystalline Ni films irradiated with well separated beams of ions of different nature, namely ions of inert (He⁺, Ne⁺, Ar⁺, Kr⁺, Xe⁺) and reactive (N⁺ and O⁺) gases. The Ni films were prepared under vacuum conditions (P? 3·10^?6Pa during evaporation) preventing an appreciable contamination of the films with impurities. The samples were irradiated at T? 300 K with ion beams of energies from 10 to 100 keV in the dose range between 5·10¹⁶ cm^?2 and the value leading to sample destruction.

Irradiation with noble gas ions revealed no phase transitions in the Ni films. A similar result was obtained in irradiation of Fe and Cr films with He⁺ ions. The bombardment of Ni films with reactive gas ions does cause changes in the lattice structure of the samples under study, depending on the nature of the bombarding ions. The N⁺ ion bombardment gives rise to the hcp phase with the lattice parameters typical of the Ni₃N compound, and the O⁺ ion bombardment results in the fcc phase with the NiO-type parameter.

The conclusion is drawn on the chemical origin of the phase transformations in the Ni films under ion bombardment. The necessity of revising the concept about the polymorphous nature of phase transformations induced in the films of transition metals by ion bombardment is substantiated.     

On the nature of the phase transition in a class of lattice gauge theories

We investigate the connection between the phase transition recently found by Anthony in a variant of SU(2) lattice gauge theory and various mechanisms known to produce phase transitions in lattice gauge theories.     

On the relaxation nature of the glass transition of amorphous polymers and low-molecular amorphous materials

Physics of the Solid State - The relative temperature range (δT g /T g ) characterizing the liquid-to-glass transition is a single-valued function of the fluctuation volume fraction f g frozen...     

The double sine-Gordon equation: On the nature of internal oscillations of the 2π-kink

Internal oscillations of the 2π-kink are treated within the harmonic approximation. The frequency and wave function dependences on the parameter of the equation are determined.     

On the nature of the dhcp to fcc transition under pressure in Pr and Pr-Th alloys

The results of electrical resistance (R), thermoelectric power (TEP) and X-ray diffraction measurements on praseodymium (Pr) and its alloys with thorium under pressure are reported. The maximum inR vsP curve exhibited by Pr persists only in the dhcp phase of PrTh alloy. X-ray measurements confirmed that in the alloys also the maximum inR vsP curve is due to the dhcp → fcc transition. Thus the behaviour of Pr and Pr-Th alloys is different from that of La and its alloys with Ce and Th where the maximum in theR vsP curve is electronic in origin and is exhibited by the dhcp, fcc and dist fcc phases.     

Admissibility of transition from the Smolukhovskii integral equation to the Einstein-Fokker-Planck differential equation

For Markov processes we consider limits for the growth rate of the probability density w(t_o, x_o; t, x) of the transition from state x_o at time to to states for which x lies between x and x + dx at time t. These limits follow from the condition of admissibility of transition from the Smolukhovskii integral equation to the Einstein-Fokker-Planck differential equation (EFP). We examine the influence of these limits on the form of the coefficients in EFT. The indicated examination is performed for the prelimit region as well, that is, the region at the end of which we have w(t_o, x_o; t, x) 0.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 99–104, October, 1986.The authors are deeply grateful to D. M. Sedrakyan and A. O. Melikyan for their interest in this work and useful comments.     

The nature of glass transition in alcohols

Evidence is presented to show that the observed glass transition process in simple alcohols may be represented as a hard to resolve combination of two glass transition processes: one due to the hydrogen (H-) bonded molecules and the other due to the non H-bonded molecules in the system. The experimentally observed secondary relaxation process is shown to be intermolecular in nature and corresponds to the latter glass transition process. A detailed discussion of the dielectric and mechanical-relaxation studies in the H-bonded systems is made.     

The nature of explosive percolation phase transition

In this Letter, we show that the explosive percolation is a novel continuous phase transition. The order-parameter-distribution histogram at the percolation threshold is studied in Erd?s-Rényi networks, scale-free networks, and square lattice. In finite system, two well-defined Gaussian-like peaks coexist, and the valley between the two peaks is suppressed with the system size increasing. This finite-size effect always appears in typical first-order phase transition. However, both of the two peaks shift to zero point in a power law manner, which indicates the explosive percolation is continuous in the thermodynamic limit. The nature of explosive percolation in all the three structures belongs to this novel continuous phase transition. Various scaling exponents concerning the order-parameter-distribution are obtained.