Hideoki Hoshino

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.

The effect of the hydrostatic pressure on the electrical conductivity of silver iodide

Abstract The electrical conductivity of the γ- and β-AgI pellets has been measured as a function of hydrostatic pressure up to 3300 kg/cm 2 in the temperature range between 10 and 100°C. The activation volumes determined from the data show a strong temperature dependence; in the γ phase they are negative at 20°C and become more positive as the temperature rises, while in the β phase they are negative and more negative with increasing temperature. These trends are remarkably different from those in AgCl and AgBr. These results are discussed on the basis of the continuum model due to Keyes. It is pointed out that the effect of thermal expansion coefficient may be important in order to interpret the large change in the activation volume of γ- and β-AgI.

Thermoelectric power of ionic crystals—III Thermoelectric power and ionic conductivity of potassium bromide containing barium bromide

Abstract The thermoelectric power of sodium bromide has been measured as a function of temperature between 580 and 720°, using platinum metal electrodes. Measurements were made on pure materials, and also on materials containing 288 × 10 −6 mole fraction of barium bromide. The heat of transport of the cation vacancy is found to be −0.75 eV and that of the anion vacancy is the value of the order of −0.60 eV in the temperature range 580–720°. Conductivity measurements were also made on the specimens doped with barium bromide as a function of temperature between 450 and 570°. The value of the energy of activation for cation vacancies was 0.80 eV. These experimental data are discussed from the viewpoint of the general theory of thermoelectric power proposed by Shimoji and Hoshino.

Ionic conductivity of lead bromide crystals

Abstract The ionic conductivity of pure and NaBr-doped PbBr2 crystals has been measured in the temperature range 60–320°C and in the impurity content range up to 3 × 10−3 mole fraction. The data show that the effect of association between impurity cations and anion vacancies is too large to be neglected. The mobility, μ, the concentration, xn0, of anion vacancies and the association constant, K3, are obtained, respectively, as follows: μ = ( 0.84 T ) exp ( −0.23 eV kT )( cm 2 V sec ), ξ n 0 = 3.2 × 10 2 exp ( −0.60 eV kT )( mole fraction ) ξ n 0 = 3.2 × 10 2 exp ( −0.60 eV kT )( mole fraction ) and K 3 = 0.12 exp ( −0.25 eV kT )( mole fraction ) −1 The measurements have also been made on pressed pellets of pure and KBr-doped PbBr2, whose conductivity values are higher than those of the crystals.

Thermoelectric power of ionic crystals—I general theory

Abstract The expression for the thermoelectric power of alkali halide crystals in contact with inert metallic electrodes is derived by considering, (i) the interactions between lattice defects, and (ii) the effect of a charged surface of the salt at the interface between the salt and the metallic electrodes with respect to the heterogeneous part. Non-equilibrium statistical mechanics of the homogeneous thermoelectric power of these systems is also discussed on the basis of the Fokker-Planck equation and it is found that the heat of transport is equal to the heat of activation. This is an extended form of the method of Allnatt and Rice for thermal diffusion. The comparison of our expression with experimental results on the KCl crystal may suggest that the difference of thermoelectric power between the pure- and the doped-crystals may mainly be due to the change in the number of the anion vacancies and that of the cation vacancies as well as the difference of the number of conduction electrons localized on the crystal surface in each case.

Electrical conductivity of GeTe glasses under hydrostatic pressure

Abstract The electrical conductivity of some Geue5f8Te bulk glasses has been measured between 10 and 80°C under hydrostatic pressure up to 3000 bar. The electrical conductivity (σ) of as-prepared, amorphous samples can be expressed by an equation: σ = A exp (− B / kT ). For Ge 17 Te 83 glass, the pressure dependences of the constants, A and B , are: (d ln A /d p ) = −3.2 × 10 −4 bar −1 and (d B /d p ) = − 2.1 × 10 −5 eV · bar −1 . The results are analysed in terms of the low-mobility band model of Mott-CFO for amorphous semiconductors.

The Ionic Conductivity and Thermoelectric Power of the Superionic Conductor Ag3SBr

The electrical conductivity and thermoelectric power of the superionic conductor Ag 3 SBr were measured in the temperature range from 293 K to 493 K. Considerable deviations from the Arrhenius law was observed in the results of the ionic conductivity. The temperature dependence of the thermoelectric power of this system was found to be very different from that in other superionic conductors. The electrical conductivity measurements were also made down to 93 K; a discontinuous change was observed near 133 K, corresponding to the β-γ phase transition. A model theory of ionic conduction is proposed, in which characteristic features of the crystal structure are taken into account. The experimental results of this system appear to be interpreted qualitatively in terms of this model.

Ionic conductivity of potassium bromide and sodium bromide crystal coloured with bromine

Abstract The d.c. conductivity of KBr and NaBr crystals, in pure and BaBr2 doped states, has been measured under 70 mmHg bromine gas in the temperature range between 400° and 540°C. The conductivity values are higher than those in vacuum, while the magnitude of activation energies is not different in both cases. The V-bands have been observed for the specimens used in the conductivity measurements. The similar absorption results have been obtained for the aqueous solutions of KBr and NaBr containing Br2 and BaBr2 + Br2, respectively. The V-bands observed in NaBr crystals are the first example obtained by heating in bromine gas. The enhanced conductivity under the bromine atmosphere suggests that the cation vacancies introduced by the dissolution of bromine atoms are not always bound in the V-centres. The model proposed by Hersh is compatible with the present results.

Thermoelectric power of ionic crystals—V. Thermoelectric power of potassium bromide and sodium bromide using bromine gas electrodes

Abstract The thermoelectric powers of single crystals of KBr and NaBr, undoped and doped with BaBr 2 , were measured as a function of temperature between 400–540°C using bromine gas electrodes. Slight discolouration of the crystals, observed after the thermoelectric power measurements, suggests that stoichiometric excess of bromine presumably yield cation vacancies and holes. The transport numbers of the holes can be neglected under the experimental condition of interest, as inferred from Mollwos work. The experimental results of the thermoelectric power are interpreted in terms of theoretical expressions for homogeneous and heterogeneous thermoelectric power. The values of heats of transport of both cation- and anion vacancies are in agreement with those of heats of activation for migration of respective ions, as predicted from the non-equilibrium theory based upon the Fokker-Planck equation (papers I and III of this series). It is quantitatively shown that the heterogeneous thermoelectric powers of the KBr and NaBr crystals being in contact with the inert metal electrodes may depend on the electrode materials and on the purity of the crystals.