Mitsuo Shimoji

Ionic conductivity and glass transition in superionic conducting glasses (Agi)1 − x(Ag2MoO4)x (x = 0.25, 0.30, 0.35): I. Experimental results in the liquid and glassy states

The electrical conductivity of the (AgI) 1 − x (Ag 2 MoO 4 ) x system ( x = 0.2, 0.25, 0.3) was measured in both the liquid and the glassy state. The temperature dependence of the observed dc conductivity in the liquid state is well expressed by the Vogel-Tumman-Fulcher (VTF) equation, while in the glassy state it is described by the Arrhenius law. In particular, an abrupt change in the temperature derivative of the conductivity was found at the glass transition temperature T g . the value of which was independently determined by thermal analysis. The frequency dependence of the conductivity in the glassy state was found only at temperatures far below T g , which may be due to the decrease in the transition rate of conducting Ag + cations. The structural relaxation of glasses appears to yield anomalous behavior of the conductivity near T g , such as deviations from the Arrhenius law, annealing and hysteresis effects.

ac conductivity of Li2ONa2OB2O3 mixed-alkali glasses: Analysis due to transition rate distribution

Abstract The complex ac conductivity of Li2ONa2OB2O3 glasses was measured in the frequency range from 5Hz to 500 kHz and in the temperature range from 200 to 400°C. The observed results were analyzed by using the complex nonlinear least square fitting technique. In order to describe the frequency dependence of the conductivity, the distribution function for the transition rate of mobile ions, P(γ), was defined and was calculated by applying the inverse Stieltjes-Hilbertt transform to the experimental values. The form of P(γ) in the present mixed alkali glasses shows a broad enhanced peak in the region of low transition rate, which demonstrates the mixed-alkali effect on the ac conductivity.

The AC conductivity of superionic conducting glasses (AgI)x−(Ag4P2O7)1−x (x = 0.8, 0.75, 0.7): Experiment and analysis based on the generalized Langevin equation

The frequency-dependent complex impedance of superionic conducting glasses (AgI)x − (Ag4P2O7)1−x (x = 0.3, 0.25, 0.20) was measured from 5 Hz to 500 kHz below room temperature. The frequency dependence of the conductivity and the electric modulus observed here cannot be expressed by a single relaxation equation, but it is well described by an equivalent circuit involving a contribution due to Jonschers universal law σ [ω] ∼ ωn (0 < n < 1). A linear relation between the DC conductivity and the relaxation time was observed irrespective of the sample compositions. These results are explained on the basis of the generalized Langevin equation associated with a non-exponential memory function. The physical basis of this approach is discussed in terms of the distribution of transition times arising from non-periodic potentials formed by immobile anions and many-body interactions among mobile cations at very high concentration in the superionic conducting glass.

Ionic conductivity and glass transition in superionic conducting glasses (AgI)1−x(Ag2MoO4)x (x=0.25, 0.3, 0.35). II: Structural relaxation and excess-free-volume theory

A theory of the structural relaxation and its effect on the ionic conductivity in superionic conducting glasses is presented by extending the excess-free-volume theory for normal glasses. The dependence of the ionic conductivity on time, temperature and cooling-heating rate is discussed for the Agl-Ag 2 MoO 4 system which forms superionic conducting glasses. The present approach is applicable to a quantitative interpretation of the bifurcation of the observed conductivity from the Vogel-Tumman-Fulcher (VTF) law to the Arrhenius type at the glass transition temperature as well as other anomalous behaviours observed in the glass transition region (deviations from the Arrhenius law, annealing and hysteresis effects, etc.). The numerical results indicate that the activation volume of a silver cation should be much smaller than the average volume per ion; this appears to be of central importance in accounting for the superionic conducting process in such silver-ion-containing glasses.

Electrical properties of the molten In-Te system

Abstract The electrical conductivity and thermoelectric power of the molten In-Te system have been measured as a function of concentration and temperature. The electrical conductivity shows a minimum around the stoichiometric composition In2Te3. The temperature coefficient of the conductivity is positive between 30 and 100 at.% Te and shows a maximum at the composition In2Te3. The values of thermoelectric power are positive and large for the semiconducting region of the system.

Glass transition and ac conductivity of Ag+ conducting glasses

Abstract Studies on glass transition phenomena of Ag+ conducting glasses are reviewed with special attention to their ac conduction properties. It is shown that experimental results obtained so far can be discussed successfully on the basis of the coupled-generalized Langevin equation and the excessfree-volume theory. High ionic conducting glasses appear to be formed under the following conditions. (i) The electrostatic force acting on one of the species is so weak as to assure its decoupled motion. (ii) Its radius is also small enough to give rise to its migration even in the glassy state.

Electrical properties of silver iodide

Abstract The electrical conductivity of γ- and β-AgI pellets was measured as a function of temperature over the range between 20 and 145 °C. The electronic contributions to the conductivity were studied by using the polarization cell (−) Ag/sample/graphite(+) in addition to experiments in an iodine atmosphere. The increase in conductivity of β-AgI due to the addition of Pbl2 was also investigated.

Thermodynamic properties of the molten thallium + tellurium system

The thermodynamic properties of molten Tl + Te alloys have been determined by the e.m.f. method. The observed integral entropy of mixing becomes practically zero and enthalpy shows a minimum at the stoichiometric composition Tl2Te. The excess stability also exhibits a strong tendency to compound formation at this composition. It is concluded from these observations, together with those of the electrical properties,1–5 that the molten Tl + Te system can be treated as two pseudo-binary systems, Tl + Tl2Te and Tl2Te + Te, and that around the stoichiometric composition Tl2Te a high local ordering can be considered because of the ionic character of the chemical bonding.

Electronic structure of liquid metals and alloys

Abstract The density of states and momentum distribution function in liquid Na–K, Ag–Au, Pb–Sn, Cu–Sn, Hg–Bi, Hg–In systems have been calculated on the basis of Edwards’ theory, using the complex energy approximation proposed by Ballentine. Various pseudopotentials and structure factors are used. It is found that the thickness of the Fermi shell for the alloys is larger than that for the pure components except for the Hg–In system. The curve of density of states at the Fermi energy is close to the free-electron value except for the Ag–Au systems, in which the modified Borchi and De Gennaro potentials are used, but its shape near the bottom of the band sometimes differs from the free-electron curve. The density of states of Hg, which has a small dip near the Fermi level when Evens’ model potential is employed, is rather free-electron-like, while the curve in the Hg–In system becomes more smooth.

Ionic Conductivity of Lead Chloride Crystals

The ionic conductivity of single crystals of pure and KCl- and NaCl-doped PbCl 2 has been measured between 90 and 400°C. The thermal disorder appears to be of unassociated Schottky defects. The expressions for the “mobility” µ and the “concentration” x n 0 of anion vacancies have been determined from a comparison between the observed isothermals and those predicted from the simple theory of Koch and Wagner in which association effects are omitted. The experimental expressions are \begin{aligned} \mu{=}(2.6\times 10^{-1}/T)\exp(-0.20\pm 0.03/kT)\ \text{cm}^{2}\ \text{volt}^{-1}\ \text{sec}^{-1} \end{aligned} and x n 0 =2.7×10 2 exp (-0.51±0.05/ k T ) in mole fraction, where k T is expressed in electron-volt. These are the first results, expressed as a function of temperature, for anion vacancies in PbCl 2 crystals.