Colossal dielectric constant in high entropy oxides

Entropic contributions to the stability of solids are very well understood and the mixing entropy has been used for forming various solids, for instance such as inverse spinels, see Nawrotsky et al., J. Inorg. Nucl. Chem. 29 , 2701 (1967) [1]. A particular development was related to high entropy alloys by Yeh et al., Adv. Eng. Mater. 6 , 299 (2004) [2] and Cantor et al., Mater. Sci. Eng. A 375–377 , 213 (2004) [3] (for recent reviews see Zhang et al., Prog. Mater. Sci. 61 , 1 (2014) [4] and Tsai et al., Mater. Res. Lett. 2 , 107 (2014) [5]) in which the configurational disorder is responsible for forming simple solid solutions and which are thoroughly studied for various applications especially due to their mechanical properties, e.g. Gludovatz et al., Science 345 , 1153 (2014) [6] and Lu et al., Sci. Rep. 4 , 6200 (2014) [7], but also electrical properties, Kozelj et al., Phys. Rev. Lett. 113 , 107001 (2014) [8], hydrogen storage, Kao et al., Int. J. Hydrogen Energy 35 , 9046 (2010) [9], magnetic properties, Zhang et al., Sci. Rep. 3 , 1455 (2013) [10]. Many unexplored compositions and properties still remain for this class of materials due to their large phase space. In a recent report it has been shown that the configurational disorder can be used for stabilizing simple solid solutions of oxides, which should normally not form solid solutions, see Rost et al., Nature Commun. 6 , 8485 (2015) [11] these new materials were called ”entropy‐stabilized oxides”. In this pioneering report, it was shown that mixing five equimolar binary oxides yielded, after heating at high temperature and quenching, an unexpected rock salt structure compound with statistical distribution of the cations in a face centered cubic lattice. Following this seminal study, we show here that these high entropy oxides (named HEOx hereafter) can be substituted by aliovalent elements with a charge compensation mechanism. This possibility largely increases the potential development of new materials by widening their (already complex) phase space. As a first example, we report here that at least one HEOx composition exhibits colossal dielectric constants, which could make it very promising for applications as large‐k dielectric materials. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Concentration dependence of thermodynamic,transport and surface properties in Ag–Cu liquid alloys

Thermodynamic, transport and surface properties of Ag–Cu liquid alloys have been investigated on the basis of a simple statistical model. The free energy of mixing, heat of mixing and entropy of mixing have been computed to understand the thermodynamic properties of Ag–Cu alloys in liquid state at 1,423 K. The concentration–concentration fluctuations in the long wavelength limit and the chemical short range order parameter have been determined to comprehend the microscopic and structural information of the alloy. The viscosity and surface tension of the alloy have been evaluated to analyze the transport and surface properties. The theoretical analysis reveals that the energy parameter is temperature dependent, and that Ag–Cu liquid alloy is a weakly interacting-phase separating system.     

Calculation of entropy of mixing of liquid metal alloys in a hard sphere system

A semi-empirical model, based on the hard sphere system, is used to determine the entropy of mixing of simple as well as compound-forming alloys. For the compound-forming liquid solutions, the method leads to fairly accurate results, showing thereby that the usual theory of hard spheres mixtures can be applied to compound forming alloys also. It has been shown that the compound formation is very sensitive to the temperature of the mixture. Numerical applications are attempted for NaHg and NaGa.     

Investigation of surface properties of liquid transition metals: Surface tension and surface entropy

In the present study, surface properties namely surface tension and surface entropy of liquid transition metals have been reported. The surface entropy of liquid Fe, Co and Ni metals has been investigated using the expression derived by Gosh et al. [R.C. Gosh, A.Z. Ziauddin Ahmed, G.M. Bhuiyan, Eur. Phys. J. B 56 (2007) 177]. To describe interionic interaction the pseudopotential approach has been used and radial distribution functions have been determined from the solution of Ornstein-Zernike integral equation. The calculated values of surface tension and surface entropy agree well with experiment. The present study shows that the expression derived by Gosh et al. leads to a good estimation for the surface entropy.     

Green's-function theory for disordered anisotropic Heisenberg ferromagnets

The Green's function theory for disordered Heisenberg Ferromagnets developed by Montgomery et al. has been extended for anisotropic systems. The densities of spin-wave states for such systems exhibit split-bands. This behavior differs qualitatively from that of the isotropic case and offers a partial explanation for the neutron scattering experiment of Buyers et al. in which they observe two well defined branches of magnetic excitations in disordered substitutional anti-ferromagnetic alloys.     

Enhancement in specific heat due to anion impurities in KCl

The specific heats of KCl containing respectively 5% KBr and 1.8% Kl, have been computed at various temperatures by Green's function technique. For the computation of specific heat, we have considered the vibrations of impurity and all its nearest neighbours, i.e., seven atoms defect space. A simple lattice dynamical model including a change of mass and a change in short-range interactions has been used in the computations. The computed results have been compared with the experimental results of Karlson for KCl:Br system and Kvavadze et al. for KCl:I system. A good agreement is found between them.     

Thermophysical properties of undercooled liquid Co-Mo alloys

Using electromagnetic levitation in combination with the oscillating drop technique and drop calorimeter method, the surface tensions and specific heats of undercooled liquid Co-10 wt% Mo, Co-26.3 wt% Mo, and Co-37.6 wt% Mo alloys were measured. The containerless state during levitation produces substantial undercoolings up to 223 K (0.13 T _L), 213 K (0.13 T _L) and 110 K (0.07 T _L) respectively for these three alloys. In their respective undercooling ranges, the surface tensions were determined to be 1895 m0.31(T m1744), 1932 m0.33(T m1682), and 1989 m0.34(T m1607) mN m^?1. According to the Butler equation, the surface tensions of these three Co-Mo alloys were also calculated, and the results agree well with the experimental data. The specific heats of these three alloys are determined to be 41.85, 43.75 and 44.92 J mol^?1 K^?1. Based on the determined surface tensions and specific heats, the changes in thermodynamics functions such as enthalpy, entropy and Gibbs free energy are predicted. Furthermore, the crystal nucleation, dendrite growth and Marangoni convection of undercooled Co-Mo alloys are investigated in the light of these measured thermophysical properties.     

Liquid-vapor transition driven by bond disorder

We report grand-canonical Monte Carlo simulations of an equimolar mixture of hard colloids coated with long polymers that have a complementary functionalization. Such systems have the potential to function as self-healing materials. Under conditions where the complementary polymer ends are strongly associated, we observe a first-order vapor-liquid transition from a dilute gas of colloidal dimers to a dense, liquid-like phase. This transition is driven exclusively by the increase in entropy associated with bond disorder-an effect that was predicted theoretically by Zilman et al. [Phys. Rev. Lett. 91, 015901 (2003)10.1103/PhysRevLett.91.015901]. Our simulations rationalize experimental observations by Schmatko et al. [Soft Matter 03 (2007) 703.].     

Construction of free-energy diagrams of amorphous alloys

Summary Free-energy diagrams of amorphous alloys are constructed using Miedema's semiempirical model of heats of formation. These diagrams account for the experimental glass-forming concentration range in binary alloys of transition metals. One of the main factors controlling glass formation is the elastic contribution to the heat of mixing of the solid solution phase. Free-energy diagrams of this kind are also useful for interpreting some characteristic processes occurring in amorphous systems, such as the spontaneous vitrification observed by Von Allmen and coworkers in several Ti-based and Nb-based alloys. The authors have agreed not to receive proofs for correction.     

地层油气的相平衡热力学研究

地层油气的相平衡热力学研究王利生（北京理工大学化工学院北京１０００８１）关键词混合规则，状态方程，油藏流体，相平衡１链状分子的普遍化范德华配分函数链状分子的转动和振动运动会受阻于其它分子的运动，因而其配分函数中的转动和振动贡献与温度、密度均有关，被分...     

Mixtures of hard spherocylinders and hard spheres

Monte Carlo simulations have been performed for equimolar mixtures of hard prolate spherocylinders of length: breadth ratio 2:1 and hard spheres, in the fluid region. Two systems have been studied. In the first the breadth of the spherocylinder was equal to the hard sphere diameter, and in the second system both components were of equal molecular volume.

The compressibility factor, PV/NkT, has been obtained for both mixtures at four reduced densities (packing fractions) from 0·20 to 0·45. The results have been compared with the predictions of several analytical equations appropriate to mixtures of hard convex molecules, and an equation due to Pavlicek et al. was found to be very accurate. The results have been used to calculate the excess volumes of mixing at constant pressure, in an attempt to establish the relative importance of the effects of differences in molecular volume and shape on the thermodynamic properties.

The structural properties of the mixtures have also been investigated by calculating pair distribution functions for the three types of pair interactions present in these mixtures.     

Theoretical assessment on mixing properties of liquid Tl–Na alloys

Thermodynamic and structural properties of mixing of molten Tl–Na alloys at 673 K have been investigated using quasi-chemical model. To understand the mixing behaviour in more detail, emphasis is placed on the role of interaction energy term, and viscosity and surface tension of the alloys have also been analysed under statistical considerations. Our study shows negative deviation from the Raoultian behaviour in the properties of Tl–Na alloy thereby indicating hetero-coordination in the Tl–Na melt at 673 K in the full range of concentration. Theoretically, computed thermodynamic data at 673 K agree very well with the corresponding experimental data. The viscosities of the alloys computed from Kaptay equation show small negative deviation and those computed from Singh and Sommer’s formulation show small positive deviation from ideal values while the Budai-Benko-Kaptay equation predicts noticeable negative deviation in Na-rich end and positive deviation in Tl-rich end of the composition. The calculations of surface tension reveal that results obtained from layered structure approach and compound formation model are in good agreement in the Na-rich side and in reasonable agreement in Tl-rich side of the composition, while those computed from Butler equation show noticeable deviations in the intermediate compositions. Both the viscosity and surface tension of liquid Tl–Na alloys increase with addition of Tl-component, viscosity having approximately linear variation with concentration. The study shows that there is non-linear variation in surface composition with bulk concentration and for most of the compositions the surface of the alloy is enriched with Na-atoms which segregate to the surface.     

On the tight binding theory of the heats of formation

The accuracy of a recently proposed simple analytic theory of the heats of formation ΔH of transition metal alloys is demonstrated by comparison with the tight binding coherent potential approximation calculations of Van der Rest et al. The d charge transfer is evaluated within a model that includes explicitly the deformation of the pure metal bands on alloying.     

Solid/liquid interfacial free energies in binary systems

The interfacial segregation and the free energy of segregation for solid/liquid interfaces between binary solutions are computed for the (111) boundary of face-centered-cubic crystals. A lattice-liquid interfacial model and pair-bonded regular solution model are employed in the treatment with an accommodation for liquid interfacial entropy. It is concluded that the zone of compositional transition across the interface is generally a few atomic layers in width and is moderately narrower for ideal solutions. The free energy of the segregated interface depends primarily upon the solid composition and the heats of fusion of the component atoms, the composition difference of the solutions, and the difference of the heats of mixing of the solutions. Master plots are presented for predicting the segregation and interfacial free energies in general binary systems.     

Unified approach to superposition states of the quantized radiation field

Summary In the recent years various and interesting superposition states of the quantized radiation field were investigated in the literature, such as that involving two number states by Wodkiewiczet al.; that involving two coherent states by Hillery and Gerryet al.; that involving two squeezed states by Xinet al., etc. Here we study a general one-parameter superposition state which unifies those states and others in the literature, all becoming a particularization of ours. General expressions characterizing the physical properties of the field are obtained. The role played by the present superposition state as an alternative interpolating state is also discussed. The authors of this paper have agreed to not receive the proofs for correction.     

Entropy of MgO based on the Stacey equation of state

In the present communication we have modified the earlier calculations for the compression dependence of entropy of MgO using recent experimental data and more accurate equation of state. We have estimated the thermal expansivity with the help of the Anderson–Isaak equation at different compressions and selected temperatures up to the melting temperature of the solid. P–V relationship and compression dependence of isothermal bulk modulus are computed with the help of the Stacey equation of state. The results have been compared with those recommended by Cynn et al. [J. Phys. Chem. 99/19 (1995) 7813]. It is found that the entropy decreases with increasing compression along an isotherm.     

Thermodynamic functions of a spin glass

We have measured the specific heats of several dilute ZnMn alloys, and from these results have found simple analytic expressions for the free energy, internal energy, entropy and specific heat of this typical spin glass alloy.     

Lynden-Bell and Tsallis distributions for the HMF model

Systems with long-range interactions can reach a Quasi Stationary State (QSS) as a result of a violent collisionless relaxation. If the system mixes well (ergodicity), the QSS can be predicted by the statistical theory of Lynden-Bell (1967) based on the Vlasov equation. When the initial condition takes only two values, the Lynden-Bell distribution is similar to the Fermi-Dirac statistics. Such distributions have recently been observed in direct numerical simulations of the HMF model (Antoniazzi et al. 2006). In this paper, we determine the caloric curve corresponding to the Lynden-Bell statistics in relation with the HMF model and analyze the dynamical and thermodynamical stability of spatially homogeneous solutions by using two general criteria previously introduced in the literature. We express the critical energy and the critical temperature as a function of a degeneracy parameter fixed by the initial condition. Below these critical values, the homogeneous Lynden-Bell distribution is not a maximum entropy state but an unstable saddle point. Known stability criteria corresponding to the Maxwellian distribution and the water-bag distribution are recovered as particular limits of our study. In addition, we find a critical point below which the homogeneous Lynden-Bell distribution is always stable. We apply these results to the situation considered in Antoniazzi et al. For a given energy, we find a critical initial magnetization above which the homogeneous Lynden-Bell distribution ceases to be a maximum entropy state. For an energy U=0.69, this transition occurs above an initial magnetization M_x=0.897. In that case, the system should reach an inhomogeneous Lynden-Bell distribution (most mixed) or an incompletely mixed state (possibly fitted by a Tsallis distribution). Thus, our theoretical study proves that the dynamics is different for small and large initial magnetizations, in agreement with numerical results of Pluchino et al. (2004). This new dynamical phase transition may reconcile the two communities by showing that they study different regimes.     

Screening-Dependent Study of Superconductivity in 3d-Transition Metals Binary Alloys Superconductors

In the present article, we report the screening-dependent study of the superconducting state parameters （SSPs）, viz. electron-phonon coupling strength A, Coulomb pseudopotential μ^＊, transition temperature TC, isotope effect exponent a, and effective interaction strength No V of 3d-band transition metals binary alloys superconductors have been made extensively in the present work using a model potential formalism and employing the pseudo-alloy-atom （PAA） model for the first time. Five local field correction functions proposed by Hartree （H）, Taylor （T）, Ichimaru-Utsumi （IU）, Farid et al. （F） and Sarkar et al. （S） are used in the present investigation to study the screening influence on the aforesaid properties. The present results of the SSPs obtained from H-screening are found in qualitative agreement with the available experimental data wherever exist.