Structure and ionic transport studies of sodium borophosphate glassy system

We have studied the frequency dependent conductivity of the semiconducting cadmium vanadate glasses of compositions xV2O5–(1−x)CdO where x = 0.6, 0.7, 0.8 and 0.9 in the temperature range 93–423 K and in the frequency range 10 Hz–2 MHz. We have observed sub-linear frequency dependence and weak temperature dependence of the ac conductivity. We have analyzed the experimental results in the framework of various theoretical models based on quantum mechanical tunneling and classical hopping over barriers. It has been observed that the temperature and frequency dependence of the ac conductivity is consistent with the overlapping large polaron tunneling model, while the classical barrier hopping models fail to interpret the data.

https://iopscience.iop.org/article/10.1088/0953-8984/20/03/035203/pdf

Frequency dependent conductivity of cadmium vanadate glassy semiconductor

Interface effect on the silver ion conductivity during the crystallization of AgIAg2OV2O5 glasses

Investigations on silver iodide silver oxysalt glass ceramics

Glass formation and electrical conductivity studies of melt quenched and mechanically milled 50Li2O:(50 − x) P2O5:xB2O3

Superionic conducting glasses in the Agl-Ag2O-V2O5 system were prepared by heating the appropriate amounts of raw materials at 723 K and quenching in liquid nitrogen. The polycrystalline materials were prepared by slowly cooling the melt to room temperature. X-ray diffraction was used for material characterization. The electrical conductivity of the pulverized samples, pressed together with an electrode mixture of silver and electrolyte (1:2 by weight) under 5000 kg cm−2 pressure to form pellets 10 mm in diameter and 2 to 3 mm in thickness, was measured in the temperature range 300 to 365 K at 1 kHz. The ionic conductivities of the glasses were always higher than those of their polycrystalline counterparts, while their activation energies were also slightly higher. Conductivity measurements on annealed glassy samples indicated that the conductivity decreases with the time of annealing, and reaches a constant value which is nearly the same as that of the polycrystalline sample. Electronic conductivities of both types of sample were obtained by using Wagner's polarization cell technique, which showed that the electronic conductivity for both types was five orders of magnitude less than the total conductivity. Typical galvanic cells having the configuration Ag,electrolyte/electrolyte/C,electrolyte,I2 were constructed and the silver ion transport number was calculated by the e.m.f. method.

The superionic Agl-Ag2O-V2O5 system: Electrical conductivity studies on glass and polycrystalline forms

Silver phosphovanadte vitreous electrolytes

Superionic conductors have attracted much attention because of their unique transport properties and technological application in solidstate batteries [1], electrochromic displays [2], etc. Solid silver ion conductors showing high ionic conductivity at ambient temperature have been obtained by either cationic or anionic substitution of AgI [3]. Unlike most of the cationsubstituted AgI-type solid electrolytes, anionsubstituted ones are not only inert towards moisture and iodine, but can also be prepared in the glassy state [4]. Once in the glassy state, these materials have many advantages over the materials in the polycrystalline state, such as isotropic properties, ease of forming, no grainboundary disks, formation of thin films, higher conductivities [5, 6], etc. In the present work ionic conductivity and thermoelectric powder studies on the 4AgI-Ag3VO4 system has been undertaken and its conductivity compared with the corresponding glassy system. Silver vanadate was prepared [7] by the addition of an aqueous solution of AgNO 3 to a saturated solution of ammonium meta-vanadate containing sodium acetate and concentrated ammonia liquid. A yellow precipitate was formed which turned into brown after settling. This was filtered out and dried at l l 0 ° C in a nitrogen atmosphere for 24h. Silver vanadate, thus prepared, was vacuum sealed in glass ampoules with Analar-grade silver iodide in the molar ratio 1:4 and heated at 400°C for 48h; the product was then cooled to room temperature. X-ray analysis of this compound indicated that the most intense lines of AgI and m g 3 V O 4 w e r e not present in this new compound formed, which may be tentatively written as Ag7IaVO 4. Total conductivity was measured using a 1-kHz impedance bridge (GR1650) on pellets of the compound formed under a pressure of 4000kgcm -2 with electrodes of a mixture of silver and the electrolyte, to minimize contact polarization. Fig. 1 shows a typical plot of log aT against reciprocal of absolute temperature for a pellet annealed at 100°C in vacuum for 12h. From the slope of the graph, the activation energy for Ag ÷ ion conduction has been found to be 0.185eV. The conductivity at room temperature (300K) was 5.3 x 10-3Q -1 cm -1. The high ionic conductivity and low activation energy suggest that silver ions in this new compound may be statistically distributed in the lattice taking an averaged structure as in other silver ion conductors [8]. A home-built apparatus has been used for thermoelectric power (TEP) measurements. The thermocell was of the following configuration: Ag(T) I Ag714VO41Ag(T + A T). The expression for thermoelectric power, 0, of a superionic conductor [8] can be written as

Transport studies on the superionic system 4AgI-Ag3VO4: conductivity comparison with the corresponding superionic glass

Deposition of thin films of the solid electrolyte Ag7I4VO4 by an electrodeposition technique is discussed. The X-ray diffraction technique has been used for the characterization of the films. Measurement of a.c. electrical conductivity in the temperature range 300–400 K showed that films deposited at 313 K and at a current density of 8 mAcm−2 are of the best quality, having a typical conductivity of 1.5 x 10-3Ω-1cm-1 at room temperature (305K) with an activation energy of 0.2eV. Dielectric studies carried out on the best quality films showed that Ag7I4VO4 possesses a high value of dielectric constant (∼ 105). The frequency dependence of the dielectric constant is explained as due to an interfacial polarization phenomenon. The behaviour of the dielectric ion suggests a Debye-type relaxation.

Rajiv Kaushik

Papers

The superionic Agl-Ag2O-V2O5 system: Electrical conductivity studies on glass and polycrystalline forms

Silver phosphovanadte vitreous electrolytes

Transport studies on the superionic system 4AgI-Ag3VO4: conductivity comparison with the corresponding superionic glass

Transport studies on thin films of Ag7I4VO4 solid electrolyte