Showing papers on "Ionic conductivity published in 1970"

Thermal expansion of NaCl, KCl and CsBr by X‐ray diffraction and the law of corresponding states

Abstract: The coefficients of thermal expansion of NaCl, KCl and CsBr are determined accurately at different temperatures using a diffractometer, Geiger counter, chart recorder and a specially designed furnace. Equations are given for the variation of the lattice constants with temperature. The temperature dependence of the thermal expansion at high temperatures is shown to be related to the concentration of thermally generated Schottky defects. The energies of formation of Schottky pairs in the three halides are estimated and are found to be consistent with those deduced from ionic conductivity studies. The reduced parameters α/(α)M/2 and T/TM give a common curve for all the halides, TM being the melting point and (α)M/2 the value of α at T = ½ TM. The curve is a straight line in the limits ~ 0.30 < T/TM < ~ 0.65 and is found to deviate considerably at higher temperatures. Assuming that the deviation is due to defects, the energies of formation of Schottky defects for the varies halides of Li, Na, K, Rb and Cs are estimated and found to agree excellently with the experimental and theoretical values.

Ionic conduction in polymer films: II. Inhomogeneous structure of varnish films

Abstract: Ionic conduction in polymer films is of two types. Inverse conduction, I, occurs when the resistance runs counter to that of the external solution, and Direct conduction, D, when the resistance follows that of the external solution. The distribution of areas having D properties has been established for films of a pentaerythritol alkyd, a phenol-formaldehyde tung oil and a polyamide-cured expoxide varnish, and it is shown that D conduction cannot be ascribed to capillaries, unless they are of molecular dimensions. It is concluded that these films have a very heterogeneous structure and that I and D areas are brought about by differences in crosslinking density within the film.

Ionic Conductivity of Potassium Bromide Crystals

Abstract: The electrical conductivity of pure KI, KI + SrI2, and KI + K2CO3 single crystals was measured as a function of temperature. A method for calculating ionic transport parameters from these results w...

Solid Ionics—Solid Electrolyte Cells

Abstract: The characteristics of the solid electrolyte cells Ag /RbAg4IJTe and Ag/RbAg4Is/Se have been studied. The open-circui t voltages of these solid electrolyte cells were 0.217V and 0.265V, respectively, at 20~ These cells could discharge in the temperature range of --75 ~ to 150~ Only a small polarization was observed at relat ively high current density discharge. Diffusion coefficients of Ag in these systems were also evaluated from the t imedependent behavior of the cell voltage as a function of current density. Although the various types of solid electrolyte cells have been investigated by many authors (1-3), most of them were able to discharge only in the microampere range at room temperature, the reason being the poor conductivi ty of the electrolyte used. Recently, as higher ionic conductivi ty solid electrolytes have been found (4-8), a high performance solid electrolyte cell operating in a mil l iampere range at ambient temperature has been developed. Previous investigations on solid electrolyte have dealt almost exclusively with the simple compounds like silver halides, the highest conductivi ty of which was between 10-6 and 10 -5 ohm -1 cm -1 at room temperature. In recent years, in o r d e r to find high ionic conductivi ty solids, the solid state reaction products of b inary and te rnary systems have been studied by Takahashi, Bradley and Owens, and Ag3SI (4), Ag2Hg0.25So.sI1.5 (5), Ag4HgSe212 (6), and RbAg415 (7, 8) have been found to have high ionic conductivities at room tempera ture (Table I) . Accordingly by using these high ionic conductivity solids as electrolytes, it is possible to make an excellent solid electrolyte cell by combining it with a suitable electrode. As silver ions are charge carriers in these compounds, silver is always used for the anode. The cathode mater ia l of solid electrolyte cells should have the properties of: (i) showing as positive a potential as possible, (ii) ease of forming thin film, (iii) a low discharge polarization, and (iv) discharge product funct ioning as a silver ion conductor. Requirements i and ii are necessary for at taining compactness and high voltage of the cell, while requirements iii and iv are for obtaining a high current density. Takahashi et al. (9) reported a solid electrolyte cell, Ag/Ag~SI/I2, and Argue et al. (10) the cell Ag/RbAg4IJRbI3, with cell voltages of 0.67 and 0.66V, respectively, and these cells can discharge at relat ively high current density. The ionic conductivi ty of solids such as Ag~SI and RbAg415 is relat ively unstable in iodine atmosphere, especially at high temperature, and iodine vapor is so highly corrosive for metals, that the celI must be gastight. In this paper a solid electrolyte cell is described in which the vapor pressure of the cathode mater ial is very low over a wide temperature range and the high voltage * E l e c t r o c h e m i c a l S o c i e t y A c t i v e M e m b e r . is main ta ined dur ing discharge even at a high current density. Results of our search for substances which satisfy the above stated requirements have indicated te l lur ium and selenium to be excellent. Te l lur ium is a solid having a very low vapor pressure and high electrical coDductivity (2.6 ohm -1 cm -1 at 20~ at room tempera ture and a mel t ing point of 450~ Fur thermore, te l lur ium is capable of forming a th in film easily by vacuum evaporation. The mel t ing point of selenium is 217~ and the vapor pressure at room tempera ture is low enough. The electrical conductivi ty of selenium, 10 -5 ohm -1 cm -1 at room temperature, is substant ial ly less than that of tel lurium. Selenium can also form a thin film readily by vacuum evaporation. In this paper, the performances of the cell Ag /RbAg4 l JTe or Se are described.

Ionic Conductivity of NaCl: SrCl2 Crystals

Abstract: The ionic conductivity of NaCl crystals highly doped with SrCl2(10−5 ≤ c ≤ 2 × 10−2, expressed in molar fraction) has been measured from room temperature to the melting point. In this wide range of concentration a unique value for the migration energy for the cation vacancy has been found: 0.75 ± 0.02 eV. With this value all the parameters for the creation and motion of lattice defects have been determined. Simple association theory could not explain the observed results. The Debye–Huckel approach was used to account for the observed absence of association at high temperature. Quenching experiments from high temperatures were performed on these doped crystals and a saturation limit of 8 × 10−4 was found for the dilution of dipoles in the matrix. The effect of clustering of these dipoles was followed by quenching from different annealing temperatures.

Direct-current conductivity of poly(ethylene terephthalate)

Abstract: There have been several previous studies of the dc conductivity of poly(ethylene terephthalate). Disagreement among the various authors indicates the difficulties inherent in this measurement: several authors [1,2] found evidence for ionic conduction through a hopping process; others [3,4] proposed conduction by electrons injected through a barrier.

The effect of high fields on the conduction of glasses containing iron

Abstract: Electronic conduction in iron-containing glasses has been studied at high fields and compared with high-field ionic conductivity in glasses containing alkali. Both processes show a Poole-Frenkel effect at fields greater than 2 × 105 V cm−. The combined effects of field and temperature are in agreement with an expression of the form log i = a − (b − cE 1 2 )/T . Dielectric constants calculated from c range from 16 to 26 and do not appear to be directly related to the dielectric properties of the bulk materials. The two types of conduction may be distinguished by the values of a and b but not of c. It is suggested that the similarity between electronic and ionic conduction is basically due to the importance of the Coulomb forces which explain not only the high-field effects but also the dielectric relaxation observed in both systems.

Ionic Conductivity and Association in CdF2

Abstract: The ionic conductivity of pure, yttrium‐doped, and sodium‐doped cadmium fluoride has been determined from room temperature up to a maximum temperature of 500°C. Results show the mobile defect to be fluorine vacancies with an activation energy of motion of 0.44 eV. A mechanism is developed for the conversion of yttrium‐doped CdF2 to a semiconductor based on vacancy motion. An anomalous conductivity curve is observed in crystals containing sodium impurity. Possible explanations for this are discussed in terms of association effects.

Ionic Conductivity of Sodium fluoride

Abstract: The electrical conductivity of single crystals of pure NaF and NaF doped with CaF2 has been measured as a function of temperature from 450 to 970°C. Analyses of these data by a leastsquare method to yield the usual defect parameters have been based on two models: 1. a perfect crystal perturbed by isolated cation vacancies, isolated anion vacancies, divalent cation impurity, and divalent cation impurity-cation vacancy complexes, and 2. one which includes the long-range Coulomb interactions between isolated defects in addition to the four defects of the first model. More satisfactory agreement with the experimental results is apparent when the latter model is employed, but non-random deviations between experiment and theory were evident for both models over the entire temperature range of observation.

Disorder in Solids (Ionic Crystals and Metals)

Abstract: Important properties of crystalline solids are due to deviations from the ideal crystal structure. Lattice defects can be divided into structural defects (grain boundaries, dislocations, impurities) and intrinsic defects. The present article deals mainly with the problems and possibilities for the determination of intrinsic disorder. This disorder, which varies reversibly with temperature, plays an important role in many solid-state processes, such as diffusion, ionic conduction, and chemical reactions in the solid phase. After an introduction to the usual physical and chemical descriptions of the state of disorder, the principal methods of investigation are discussed. Special emphasis is placed on methods of determining disorder data from “anomalous” specific heats.

Electron Injection into Anodic Tantalum Oxide Assisted by Ionic Interface Polarization

Abstract: The investigation of electronic conduction processes in anodic tantalum oxide films with electrolytic and solid contacts is generally hampered by parallel ionic conductivity at high fields and the uncertain contributions of flaws, even in the case of high‐purity materials. We found that electronic conductivity could be induced reproducibly and with homogeneous current densities in the presence of thin layers of semiconducting oxides, such as and which were deposited by reactive sputtering. Experiments were carried out with electrolyte contact. The electronic current was found to follow in a wide range of current densities. A Poole‐Frenkel mechanism is proposed in which the current is controlled by thermionic emission at the ‐interface. Electronic conductivity increases as a time dependent activation process lowers the emission barrier through ionic interface polarization. The contribution of flaws to the electronic conductivity was investigated by means of the anodic printing technique. The electronic current resulting from the activation process was found to be of uniform density and unrelated to any physical flaws in the anodic tantalum oxide.

Light scattering and ionic conductivity in NaCl:Ba and NaCl:Cd single crystals

Abstract: Simultaneous measurements are made of light scattering and ionic conductivity as a function of temperature in the range 20 to 650°C on Ba- and Cd-doped NaCl single crystals submitted to different heat treatments. In case of Ba-doped crystals, the results are interpreted by changes in the decoration of the precipitates with cation vacancies; in case of Cd-doped crystals by dissolution and reformation of the precipitates as a consequence of appropriate heat treatments.

Donor, Temperature, and Pressure Dependence of the Ionic Conductivity in Iodine

Abstract: In agreement with a previous analysis it has been shown that the low temperature ionic conductivity of iodine is independent of the donor used to introduce this conductivity. A comparison of the high temperature ionic conductivity data and the polarographic half‐wave potentials shows that p‐phenylenediamine (PPD), diaminodurene (DAD), and p‐toluidine (PTD) ionize to the monopositive ion, while tetramethyl‐p‐phenylenediamine (TMPD) probably ionizes to the bipositive ion in solid iodine. From an analysis of the nonequilibrium conductivity a value (2.1 eV) could be derived for the activation energy of the motion of I2− in solid iodine, which compares well with values found for I3− and I− previously. The pressure dependence of the ionic conductivity has been measured. It was found that the free volume involved in either the transport or the generation process of the I3− ion corresponds to half the molar volume of iodine, which again lends further credence to the mechanisms proposed to explain this conductivity.

Effects of lattice defects on thermoluminfscence in lithium fluoride crystals

Abstract: The thermoluminescent output of ‘pure’ LiF single crystals is studied as a function of annealing temperature and cooling rate. The lattice defect structure is characterized using ionic conductivity measurements. The results show that the sensitivity of such crystals to irradiation is highly dependent on prior history; specifically, the intensity of the observed 105°C thermoluminescence peak depends directly on the concentration of impurity vacany pairs present. The results also show the importance of background impurities in effecting thermoluminescent sensitivity.

Electrical Transport in Ionic Crystals

Abstract: Electrical conduction in solids is caused by the directed movement of electrons, holes or ions under the action of electric fields applied from outside. The electrical conductivity σ is equal to Σi ni q1 µi for a solid obeying Ohm’s law. Here, ni is the number per unit volume of the mobile charge carriers of the 1th type, q. the charge on each such carrier and µi the mobility. There is no transport of matter when electrical conduction is by electrons or holes as in metals and semi conductors. Such a conduction can be recognised by Hall effect measurements. On the other hand, in ionic conduction, charge transport is accompanied by mass transport. Crystals like KCl are appropriately called solid electrolytes. Hall effect, is too small to be observed in this case. However, when a d.c. current is passed for a sufficiently long time through three plates of the crystal in series, the end plates should show a change of mass if the conduction is by the movement of the ions. In fact, it should be possible to deduce the transport numbers of ions. If the measurements are sufficiently accurate1–7. Even otherwise, qualitative information can be obtained as to the more mobile carriers.

The properties of point defects in ionic crystals

Abstract: This short communication summarises several features of atomistic calculations of the Characteristic energies and volume dilatations of vacancies in ionic crystals. The prediction that the volumes of formation of Schottky defects are less than the molar volume is in agreement with inferences made from radiation damage studies (LiF and MgO) but in conflict with the results on the effect of pressure on ionic conductivity (NaCl and KCI).