S. Radhakrishna

Raman and far IR studies on Ag2CdI4 and Cu2CdI4 superionic compounds

Abstract Raman spectral studies, far infrared reflection and transmission spectra for the superionic conductors Ag 2 CdI 4 , Cu 2 CdI 4 at 300 K are reported. From these studies the TO and LO modes are assigned and optical conductivity in the region 30 cm -1 -150 cm -1 are calculated. The behaviour of conductivity in this frequency region is explained on the basis of jump diffusion model.

Transport and dielectric studies on silver based molybdo-tungstate quaternary superionic conducting glasses

The molybdo-tungstate (MoO 3 -WO 3 ) combination of glass formers with silver oxide (Ag 2 O) as glass modifier and silver iodide (AgI) as ionic conductor were prepared to study the transport and dielectric properties of 60% AgI-40% ( x Ag 2 O- y (WO 3 -MoO 3 ) for x/y =0.33 to 3.0 and establish the feasibility of using these glasses as electrolytes in the fabrication and characterisation of solid state batteries and potential memory devices. The details of the preparation of glasses and methods of measurement of their capacitance, dielectric loss factor and ac conductivity in the frequency range 100 Hz–100 kHz from 30–120°C have been reported. The electronic contribution to the total conductivity, the ionic and electronic transport numbers were determined using Wagners dc polarisation technique. The observed high ionic and low electronic conductivities were attributed to the formation of ionic clusters in the glass and the effect of mixing two glass formers. The observed total ionic conductivity and its temperature dependence was explained using Arrhenius relation σ=σ 0 / T exp(− E/RT ) and the measured dielectric constant and dielectric loss were explained on the basis of Jonschers theory. The frequency dependence of dielectric constant obeys the theory based on the polarisation of ions.

Dielectric dispersion studies on Ag2Hgl4 and Cu2Hgl4 superionic compounds

Etude des proprietes dielectriques entre 10 2 et 10 6 Hz. La constante dielectrique decroit legerement avec la frequence. Les pertes dielectriques passent par un maximum pour une certaine frequence caracteristique

Silver borotungstate glasses : new electrolyte for solid state electrochemical cell

Abstract For the quaternary fast ion conducting system AgI-Ag 2 O-B 2 O 3 -WO 3 highest ionic conductivity was observed for the composition 60AgI-20Ag 2 O-20(0.1B 2 O 3 -0.9WO 3 ). This composition was used in the fabrication of solid state electrochemical cell with different types of anodes and cathodes. Cell performance was assessed by studying the open circuit voltage (OCV), polarization characteristics and discharge characteristics.

Mixed glass former effect in mol% 66.67 AgI-24.66Ag2O-8.33((1−x)B2O3−xAs2O3) quaternary amorphous solid electrolytes

Fast ion conducting quaternary amorphous solid electrolytes with chemical composition in mol% 66.67 AgI-24.66Ag2O-8.33((1 - x) B2O3-xAs2O3) for 0.1 < × < 0.9 were investigated emphasizing the influence of two glass formers on their transport properties. X-ray diffraction and differential scanning calorimetry were utilized to determine the amorphous nature and the thermal stability of these amorphous solid electrolytes for solid state battery application. Ionic and electronic conductivity studies were performed on all the electrolyte compositions to evaluate the highest conducting composition. The presence of a second glass former in the quaternary amorphous network has shown a pronounced effect on the glass transition temperature of the electrolytes. This mixed glass former effect is discussed based on the ionic radius, field strength and the valence state of the glass forming oxide cation and its role in the formation of an amorphous network.

Mixed glass former effect in AgI-Ag2O-V2O5-P2O5 quaternary amorphous solid electrolytes

Abstract In the process of investigating electrical conduction in ternary and quaternary amorphous solid electrolytes, interesting results have been obtained in the AgI-Ag2O-V2O5-P2O5 quaternary system. The present investigation reports the mixed glass former effect on the ionic and electronic conductivities and glass transition temperatures of the electrolyte compositions mol% 66.67 AgI-22.22Ag2O-11.11((1−x)V2O5-xP2O5). A double maxima was observed in the ionic conductivity at x = 0.2 and 0.7 where the electronic conductivity assumes minimum values. The glass transition temperature was observed to increase with x in analogy with amorphous semiconducting (1−x)V2O5-xP2O5- oxides. These results are discussed on the basis of the entropy of mixing two glass formers and the possible structural changes that might occur in the quaternary amorphous network due to the presence of a second glass former. The observed properties are compared to the ternary amorphous systems AgI-Ag2O-V2O5 and AgI-Ag2O-P2O5 emphasising the mixed glass former effect in light of their covalency and field strength.

Electrochemical performance of silver/molybdotungstate-amorphous-electrolyte cells with charge-transfer-complex cathodes

Abstract For the quaternary fast ion conducting system AgIAg 2 OMoO 3 WO 3 , the highest ionic conductivity, 5.1 × 10 −2 (μ cm) −1 , was observed when using an amorphous electrolyte composition of 80%AgI-13.33%Ag 2 O-6.66% (0.7MoO 3 -0.3WO 3 ). This electrolyte was used in the fabrication of solid-state electrochemical cells with the configuration (anode)/(amorphous electrolyte)/(cathode). The anode consisted of silver while a variety of organic charge-transfer-complex materials was employed as cathodes. The latter included phenothiazene, pyrene, and 2-perylene·3I 2 . Cell performance was assessed by studying open-circuit voltage (OCV), anodic and cathodic polarisation, current discharge capability, and load discharge characteristics. It was found that the cell with a 2-perylene·3I 2 cathode yielded the highest OCV (657 mV) without any anodic or cathodic polarisation. The cell exhibited an internal resistance of 32 μ and a short-circuit current of 10 mA with a rechargeability having marginal coulombic efficiency. The diffusion co-efficients of silver ion were evaluated from the time dependence of cell voltage as a function of current density. The optimum current density ( i.e. , that giving no polarisation) was fixed and the load curves were recorded to evaluate the applicability of the cells to micropower sources and low-energy-density silver batteries.

Glass formation and electrical conductivity studies of AgI-Ag2O-[xMoO3+(1−x)V2O5] x=0.1 to 0.9 system

Analar grade MoO 3 , V 2 O 5 , Ag 2 O and AgI compounds have been mixed in different ratios to form the superionic conducting AgI-Ag 2 O-[ x MoO 3 +(1− x )V 2 O 5 ] ( x =0.1 to 0.9) glasses by quenching the molten liquid in liquid nitrogen. The glassy nature of these materials have been identified from X-ray diffractogram spectra and the presence of molybdate and vanadate clusters have been identified from infrared spectra. The highest room temperature (306 K) conductivity was found to be 2.5×10 −2 Ω −1 cm −1 for the particular composition of the two network formers ( x MoO 3 +(1− x )V 2 O 5 , x =0.1). From the temperature variation of the best conductivity plot, the activation energy for the migration of silver (Ag + ) ions was calculated to be 0.37 eV. Wagners dc polarisation technique has been used to find the electronic conductivity of the glassy system and was found to be (1.587×10 −7 Ω −1 cm −1 ) much less than the total conductivity. The transport number t Ag + has been evaluated from the total and the electronic conductivity values as 0.999.

Transport and dielectric studies on 66.6% Agl-22.2% Ag2O-11.1% ((1 −x)V2O5 +xP2O5) glassy electrolytes

Etude des variations de la conductivite ionique, de la conductivite electronique, de la constante dielectrique et de la perte dielectrique en fonction de la composition du systeme

Electrical properties of thin solid films of the solid electrolyte Ag5IW2O8

Abstract A simple electrolytic method of preparing solid electrolyte Ag 5 IW 2 O 8 on a silver substrate is described. Films of different quality are formed when the electrolysis is carried out at different temperatures and current densities. X-ray diffraction studies were also carried out in order to confirm the formation of Ag 5 IW 2 O 8 films by calculating the d spacings corresponding to different reflections. The film deposited at 60°C has the best electrical properties, comparable with those of bulk Ag 5 IW 2 O 8 , and these films show an electrical conductivity of 1.6 × 10 -5 Ω -1 cm -1 at 33°C.