The influence of surface effects on Frederiks transition in nematic liquid crystal doped with ferroelectric nanoparticles

Motivated by our recent work,in this work,we present the numerical study of the anchoring effect on the Frederiks threshold field in a nematic liquid crystal doped with ferroelectric colloidal nanoparticles.Assuming weak anchoring conditions,we employ the relaxation method and Maxwell construction to numerically solve the Euler–Lagrangian differential equation for the total free energy together the Rapini–Papoular surface energy to take into account anchoring of nematic liquid crystal molecules at the substrates.In this study,we focus our attention on obtaining the phase diagrams of Frederiks transition for different values of anchoring strength which have been not computed in our previous work.In this way,the effect of nanoparticle radius,nanoparticle volume fraction,nanoparticle polarization,and cell thickness on the Frederiks transition for different values of anchoring conditions are summarized in the phase diagrams.The numerical results show that by increasing the nanoparticles size and nanoparticle volume fraction in the ferronematic system,the Frederiks threshold field is strongly reduced.     

Molecular field theory for nematic liquid crystal film with finite layers

The nematic liquid crystal film composed of n molecular layers is studied based upon a spatially anisotropic pair potential, which reproduces approximately the elastic free energy density. On condition that the system has perfect nematic order, as in the Lebwohl—Lasher model, the director in the film is isotropic. The effect of the temperature is investigated by means of molecular field theory. Some new results are obtained. Firstly, symmetry breaking takes place when taking account of the temperature, and the state with the director along the normal of the film has the lowest free energy. Secondly, the N—I phase transition temperature increases as an effect of finite sizes instead of decreasing as in the Lebwohl—Lasher model. Thirdly, the nematic order is induced in the layers near the surface in the isotropic phase.     

Thermodynamics of Phase Transitions of a Kerr Nonlinear Blackbody

We study the thermodynamics of phase transitions of a blackbody whose interior is filled by a Kerr nonlinear crystal. There is a transition temperature To, above which the Kerr nonlinear blackbody is in the normal thermal radiation state, and below which it is in the squeezed thermal radiation state. At To, the Gibbs free energy of the two phases is continuous but the entropy density of the two phases is discontinuous. Hence, there is a jump in the entropy density and this leads to a latent heat density. The photon system undergoes a first-order phase transition from the normal to the squeezed thermal radiation state.     

First Principles Study on Electronic Structure of PbFe0.5Nb0.5O3

The full potential linearized augmented plane wave (FLAPW) method is used to study the crystal structure and electronic structure properties of PbFeo.5 Nbo.5O3 (PFN). The optimized crystal structure, density of states, band structure and electron density distribution have been obtained to understand the ferroelectric behaviour of PFN.The analysis result of the density of states shows there is an obvious change of Nbd states in the paraelectric-to-ferroelectric phase transition. The polarization result shows that the contribution to ferroelectricity of Nb atoms is larger than that of Fe atoms. In ferroelectric phase there is a hybridization of Fed-Op and Nbd-Opin ferroelectric PFN. This is consistent with the result of the electronic band structure. This hybridization is responsible for the tendency to its ferroelectricity.     

Epitaxy surface effect on the first-order phase transition properties in a ferroelectric thin film

By modifying the interchange interactions and the transverse fields on the epitaxy surface layer,this paper studies the phase transition properties of an n-layer ferroelectric thin film by the Fermi-type Green’s function technique based on the transverse Ising model with a four-spin interaction.The special attention is given to the effect of the epitaxy surface layer on the first-order phase transition properties in the parameter space constructed by the ratios of the bulk transverse field and the bulk four-spin interaction to the bulk two-spin interaction with the framework of the higher-order decoupling approximation to the Fermi-type Green’s function.The results show that the first-order phase transition properties will be changed significantly due to the modification of interchange interaction and transverse field parameters on the epitaxy surface layer.The dependence of the first-order phase transition properties on the thickness of ferroelectric thin films is also discussed.     

Vapour-to-Liquid Nucleation in Associating Lennard-Jones Fluids with Multiple Association Sites

The excess Helmholtz free energy functional for associating Lennard-Jones （L J） fluid is formulated in terms of a weighted density approximation for short-ranged interactions and a Weeks-Chandler-Andersen approximation for long-range attraction. Within the framework of density functional theory, phase equilibria, vapour-liquid surface tension and vapour-liquid nucleation properties including the density profile, work of formation, excess number of particles and critical supersaturation are investigated for associating LJ fluids with different numbers of association sites （M =1,2, 3, 4） per particle. The influences of association energy and association sites on phase equilibria, surface tension and vapour-liquid nucleation properties are discussed.     

Ginzburg–Landau Free Energy of Crystalline Color Superconductors:A Matrix Formalism from Solid-State Physics

The Ginzburg–Landau(GL) free energy of crystalline color superconductors is important for understanding the nature of the phase transition to the normal quark matter and predicting the preferred crystal structure. So far the GL free energy at zero temperature has only been evaluated up to the sixth order in the condensate. To give quantitative reliable predictions we need to evaluate the higher-order terms. In this work,we present a new derivation of the GL free energy by using the discrete Bloch representation of the fermion field. This derivation introduces a simple matrix formalism without any momentum constraint,which may enable us to calculate the GL free energy to arbitrary order by using a computer.     

Paraelectric--ferroelectric interface dynamics induced by latent heat transfer and irreversibility of ferroelectric phase transitions

The temperature gradients that arise in the paraelectric--ferroelectric interface dynamics induced by the latent heat transfer are studied from the point of view that a ferroelectric phase transition is a stationary, thermal-electric coupled transport process. The local entropy production is derived for a ferroelectric phase transition system from the Gibbs equation. Three types of regions in the system are described well by using the Onsager relations and the principle of minimum entropy production. The theoretical results coincides with the experimental ones.     

The hysteresis loops of a ferroelectric bilayer film with surface transition layers

Based on the transverse Ising model in the framework of the mean field approximation,this paper discusses a ferroelectric bilayer film with the surface transition layers within each constituent slab and an antiferroelectric interfacial coupling between two slabs.The hysteresis loop of a bilayer film is investigated.The results show that the surface transition layer in a ferroelectric bilayer film plays a significant role in realizing the multiple-state memory.     

First-Principles Study of the γ Angle Deformation Path in the Wurtzite-to-Rocksalt Phase Transition in Aluminum Nitride

A new transition path （γ angle deformation path） is put forward and used to characterize the wurtzite-rocksalt transition in AlN. The enthalpy surface and the contour plot of enthalpy difference at equilibrium pressure are obtained by first-principles pseudopotential method within the generalized gradient approximation. The phase transition is needed to overcome two barriers and a metaphase arises between them. The total barrier height is 0.26eV. The pressure region of the phase transition is estimated to be 13.9-23.5 GPa, in which the experimental result is well located. Along the least barrier path, the changes of density of states and the fields of charge density difference are investigated. The similarities and differences between γ angle deformation path and the orthorhombic deformation path are analyzed.