Thermal conductivity in superionic conductors

The contribution of mobile ions to the thermal conductivity in superionic conductors is investigated by making use of the lattice gas model with a hopping term. The thermal conductivity is obtained as a function of an ion concentration and a repulsive interaction energy between the nearest neighbors. It is shown that the contribution of mobile ions to the thermal conductivity is of an Arrhenius type in the usual temperature region in which measurements are conducted.     

Specific heat and thermal conductivity of superionic conductors in the superionic phase

The temperature dependences of the specific heat and the thermal conductivity of crystalline superionic conductors LnF₃ (Ln = La, Ce, Pr), Li₂B₄O₇ and α-LiIO₃ in the superionic phase have been investigated experimentally. The specific heat C _p and the thermal conductivity K are observed to increase monotonically over a wide range of temperatures above the Debye temperature Θ_D. This increase is attributed to the relaxational interaction of high-frequency phonons with two-level systems. Fiz. Tverd. Tela (St. Petersburg) 39, 1548–1553 (September 1997)     

Atomic mechanisms of superionic conductivity in fluorite

The subsequent melting/crystallization of the two sub-lattices of CaF₂ is explored by molecular dynamics simulations. Both, heating from 100 K and cooling from 2500 K encompasses two transitions, i.e. the melting/recrystallization of the fluoride sub-lattice and the of whole crystal at different temperatures. Solid state F^? ion conductivity is observed in a temperature range of about 1500–2000 K which reflects a reasonable agreement with the experiment. A systematic study of fluoride migration revealed the atomistic mechanisms of the spontaneous formation of Frenkel defects, followed by void translocation and terminated by recombination of interstitial fluoride ions and vacancies.     

Ternary superionic conductors: Structural aspects

Summary A survey of the present state of research (both experimental and theoretical) on the structural aspects of ternary superionic conductors is presented. The discussion concentrates on the β- and β″ and the AgI-based conductors. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

High pressure studies of superionic conductors with predominant anionic conductivity

The effect of hydrostatic pressure on the ionic conductivities in α-PbF₂, β-PbF₂, β-Pb_1−x M _x ^m F_2+(m−2)x (where M^m=Na⁺, Cd²⁺, Tb³⁺, U⁴⁺), PbSnF₄, RbSn₂F₅, LaF₃ and LaF_3-1.2 mol.% CaF₂ has been investigated in the temperature range between 300 K and 700 K for pressures up to 0.30 GPa (for β-PbF₂, PbSnF₄, RbSn₂F₅) and 0.8 GPa (for LaF₃). The activation volumes of defect formation and migration, impurity defect segregation and dissociation were determined from the effect of pressure on conductivity. Keyesí treatment based on the strain energy Zener model in Grüneisen approximation was used to estimate theoretical values of the activation volumes. Paper presented at the 1st Euroconference on Solid State Ionics, Zakynthos, Greece, 11–18 Sept. 1995     

Microstructural effects on the superionic conductivity of a lithiated glass-ceramic

Three different formulations of 14 Li₂O·9 Al₂O₃·38 TiO₂·39 P₂O₅ composition (LATP) were melted, cast and crystallized. As-cast glass was characterized by differential scanning calorimetry which exhibited a distinct and strong exothermic peak around 680 °C. The peak was attributed to the crystallization of the glass. The crystallized glass (glass-ceramic) was further characterized by X-ray diffraction which showed the existence of Li_1 + xAl_xTi_2 − x(PO₄)₃ (x ⋍ 0.3)as the primary phase mixed with a small concentration of AlPO₄ and an unidentified phase. The scanning electron micrographs revealed the presence of the primary crystalline phase with an average grain size of 1 μm. Electrical characterization by AC impedance spectroscopy revealed grain and grain boundary contributions to the total conductivity. The effect of specimen processing parameters on conductivity is also investigated and discussed.     

Dynamic conductivity of superionic conductors in an interacting Brownian particle model

The mobile ion dynamics in superionic conductors is described by a many-particle Fokker-Planck equation. A time-dependent mean-field equation for the single-particle distribution is derived, which implies a general relationship between the dynamic conductivity and structural properties. We find that the low-frequency diffusive regime is governed by a renormalized single-particle potential, whereas the high-frequency vibrational response is determined by the bare interaction between the two species of conducting and lattice ions. Numerical results, based on matrix continued fractions are presented for the whole frequency-range and implications with respect to experiments are discussed.     

Correlation effects on frequency dependent conductivity: Application to superionic conductors

The Scher-Lax model for the calculation of a.c. conductivity is modified to allow for temporal and spatial correlations. If, due to, say, lattice relaxation effects, a charge is most likely to continue to move in the same direction (caterpillar mechanism), then the real part of the conductivity will saturate, at large frequencies, below the d.c. level. The reverse will be true if a bounce-back mechanism dominates. These two cases of correlation can be related to the behavior of the superionic conductors AgI and Na β-alumina, respectively. The degree of disorder in the hopping sites determines the distribution of ionic transition rates which in turn governs the details of the conductivity curve. The frequency dependent conductivity due to the motion of an ionic cluster (dimer) is also analyzed.     

Microwave conductivity evidence for order-disorder transition in the superionic conductor β-eucryptite

The impedance of LiAlSiO₄ (β-eucryptite) at 9 GHz shows a marked decrease in activation energy as the temperature is raised above 450°C, where X-ray data indicate an order-disorder transition.     

Orientational disorder,glass/crystal transition and superionic conductivity in nasicon

The relations between the orientational disorder of SiO₄(PO₄) tetrahedra and fast sodium diffusion in superionic NASICON have been studied by conductivity (complex impedance method), DSC, X-ray powder difraction and vibrational spectroscopy (IR and Raman). Sol-gel routes allow to obtain pure glassy NASICON (Na_1+xZr₂Si_xP_3-xO₁₂x≅2) in the 500−700°C temperature range. Tetragonal zirconia nucleates above 700°C and disappears at about 900°C when the isolated tetrahedra framework is formed: a high orientational static disorder of tetrahedra exists and the symmetry is rhombohedral at all studied temperatures (20−600 K). Thermal treatment above 1100°C induces a drastic decrease of the static orientational disorder and nucleation of monoclinic zirconia. The resulting compound exhibits a monoclinic symmetry at R.T. and three phase transitions, two diffuse at about 60 K and 520 K and the 423 K monoclinic-rhombohedral transition associated with the superionic conducting state. An increase in dynamic disorder (broad Rayleigh wing up to 500 cm^-1 is simultaneously observed. The lower the static disorder at low temperature, the higher the dynamic orientational disorder and the phase transitions, and the lower the activation energy of conductivity at high temperature.     

Ionic conductivity and chemical diffusion in LixCu2−xSe superionic alloys

Results of studies on the ionic conductivity and chemical diffusion coefficients of stoichiometric Li_xCu_2−xSe (0<x<0.20) ternary alloys in the temperature range 350–405 °C are presented. It is observed that in the stoichiometric copper selenide the substitution of part of copper by lithium leads to a strong change for the deterioration of ionic transport conditions.     

A theory of the microwave ac conductivity of superionic conductors with randomly modulated structure

Localized resonant absorbing states of ions due to a random potential modulating the structure of superionic conductors are shown to be responsible for ac current response maxima in high frequency tails. The theory allows for interpretation of the microwave maxima found in samples of α-AgI and β-Cu Br exhibiting strain-induced texture, and also in some polycrystalline ionic structures.     

Low-frequency,coulomb-correlated density fluctuations in superionic conductors and their influence on the conductivity

The low-frequency density and current response of diffusing ions is calculated for superionic conductors. In particular, it is shown that the peculiar dispersion of the conductivity of α-AgI at low frequencies is due to the scattering of silver ions by slowly relaxing local density fluctuations caused by the other silver ions.     

Behavior of the low-frequency conductivity of silver iodide nanocomposites in the superionic phase transition region

Physics of the Solid State - The behavior of the specific conductivity of composites based on silver iodide embedded in porous glasses with an average pore diameter of 7 ± 1 nm and in...     

Preparation,electric conductivity and dielectrical properties of Cu6PS5I-based superionic composites

Composite samples based on microcrystalline Cu₆РS₅I superionic conductors, embedded in matrices of polyvinylacetate, epoxy and conducting glue, are produced. Temperature and frequency studies of complex electric conductivity and dielectric permittivity as well as dielectric loss of the obtained composites are carried out. The effect of differences in the composite production technology on the temperature of a second-order phase transition in the superionic phase, values of electrical conductivity, activation energy and dielectric permittivity is shown.     

Thermodynamic aspects of the glass transition of silicates

The marked increase in second-order thermodynamic properties observed at the glass-transition signals the onset of configurational changes in viscous liquids. Experimental determinations in the glass-transition range will illustrate this point for thermal expansivity and demonstrate that the kinetics of volume, enthalpy and structural relaxation are identical for silicate liquids. Within the framework of the Adam–Gibbs theory, heat capacity and viscosity data may be combined to calculate configurational entropies and gain insights into the potential energy barrier to viscous flow. Finally, the considerable effect of water on the glass transition temperature of geologically relevant silicates is presented.     

具有本征低晶格热导率的硫化银快离子导体的热电性能

硫化银(Ag_2S)是一种典型的快离子导体材料,前期关于Ag_2S的研究主要集中在光电和生物等领域.最近的研究表明, a-Ag_2S具有和金属一样的良好延展性和变形能力.但是, Ag_2S的热电性能尚无公开报道.本工作合成了单相Ag_2S化合物,系统研究了其在300—600 K范围的物相变化、离子迁移特性和电热输运性质.研究发现, Ag_2S在300—600 K温度区间表现出半导体的电输运性质.由于单斜-体心立方相晶体结构转变, Ag_2S的离子电导率、载流子浓度、迁移率、电导率、泽贝克系数等性质在455 K前后出现急剧变化.在550 K, Ag_2S的功率因子最高可达5μW·cm~(–1)·K~(–2). Ag_2S在300—600 K温度区间均表现出本征的低晶格热导率(低于0.6 W·m~(–1)·K~(–1)). S亚晶格中随机分布的类液态Ag离子是导致b-Ag_2S体心立方相具有低晶格热导率的主要原因.在573 K, Ag_2S的热电优值可达0.55,与Ag_2Se, Ag_2Te, CuAgSe等已报道的Ag基快离子导体热电材料的性能相当.     

Thermodynamic aspects of Schrödinger's probability relations

Using Schrödinger's generalized probability relations of quantum mechanics, it is possible to generate a canonical ensemble, the ensemble normally associated with thermodynamic equilibrium, by at least two methods, statistical mixing and subensemble selection, that do not involve thermodynamic equilibration. Thus the question arises as to whether an observer making measurements upon systems from a canonical ensemble can determine whether the systems were prepared by mixing, equilibration, or selection. Investigation of this issue exposes antinomies in quantum statistical thermodynamics. It is conjectured that resolution of these paradoxes may involve a new law of motion in quantum dynamics.     

Electrical conductivity and permittivity of the one-dimensional superionic conductor LiCuVO<Subscript>4</Subscript>

The electrical conductivity σ^a and permittivities ?^a, ?^b, and ?^c of a LiCuVO₄ single crystal have been measured along the a, b, and c crystallographic axes, respectively, in the temperature range 300–390 K at a frequency of 10³ Hz. The temperature dependences σ(T) and ?(T) were found to be typical for superionics.