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Papers by sathya prasad

Research paper thumbnail of Electrical conductivity, TEP and dielectric studies on mol% 66.6 Agl-22.2 Ag 2 O-11.1 (0.8 V 2 O 5 -0.2 P 2 O 5 ) electrolyte material for solid state batteries

Journal of Materials Science, 1988

In the superionic conducting quarternary system Agl-Ag2O-V2O5-P2O5, the best ionic conductivity w... more In the superionic conducting quarternary system Agl-Ag2O-V2O5-P2O5, the best ionic conductivity was obtained for the composition 66.6% Agl-33.3% (2Ag2O-1 (V2O5-P2O5)), when the GF/GM ratio was varied from 0.20 to 5.0. Then fixing the GF/GM ratio at 0.50, the ratio of the glass formers V2O5 and P2O5 were varied and the highest conducting composition was obtained as 66.6% Agl-22.2 Ag2O-11.1% (0.8 V2O5-0.2 P2O5). A preliminary investigation using this material in the form of an electrolyte in a solid state electrochemical cell is reported. The polycrystalline and amorphous compounds were prepared from the same melt, by open air crucible melting and the rapid quenching technique. The ionic conductivity for the best conducting polycrystalline (hence referred as 66VP82P) and amorphous (66VP82G) samples was obtained as 8.3 × 10−3 and 4.2 × 10−2 Ω−1 cm−1 respectively. The electronic conductivity of the order 10−10 Ω−1 cm−1 was observed for 66VP82G and 10−8 Ω−1 cm−1 for 66VP82P samples. Thermoelectric power studies revealed that the charge carriers are the Ag+ ions, with an activation energy of 0.288eV for 66VP82G, which correlated well with the activation energy obtained from the conductivity measurements. The dielectric constant, dielectric loss and the loss tangent were calculated for both polycrystalline and glassy 66VP82 material. It was observed that the dielectric loss is more for the glassy material than the polycrystalline material. Solid state galvanic cells with 66.6% Agl-22.2% Ag2O-11.1% V2O5, 66.6% Agl-22.2%-Ag2O-11.1% P2O5 and 66.6% Agl-22.2% Ag2O-11.1% (0.8 V2O5-0.2 P2O5) (coded as 66V, 66P and 66VP82 respectively) electrolytes were constructed. Both polycrystalline and amorphous electrolyte cells were fabricated for a comparative study and the polarization effects were observed to be negligible in amorphous cells. The variation of open circuit voltage with temperature was reported and the current discharge curves indicate that the 66VP82 material has higher current capacity with high current drain when compared to 66V and 66P cells.

Research paper thumbnail of Electrochemical studies on solid state cells with mol % 70AgI20Ag 2 O-10(0.8V 2 O 5 -0.2P 2 O 5 ) amorphous electrolyte and organic cathodes

Journal of Applied Electrochemistry, 1989

The highest conducting amorphous solid electrolyte composition (mol %) 70AgI-20Ag2O-10(0.8V2O5-0.... more The highest conducting amorphous solid electrolyte composition (mol %) 70AgI-20Ag2O-10(0.8V2O5-0.2P2O5) in the system AgI-Ag2O-V2O5-P2O5 was investigated as an electrolyte material for solid state cells with organic cathodes by studying the electrochemical properties. The variation of open circuit voltage (OCV) with temperature, current discharge and the load characteristics were determined for the cells with iodine, tetramethyl ammonium iodide and tetrabutyl ammonium iodide as cathode materials. The cell capacities were estimated from the load characteristic curves and, in general, the cells were found to have very good stability at low current discharges even at high temperatures. In addition, it was found that the silver on the working electrode is electrochemically active and can be oxidized to Ag+ ions, making the organic cathode cells rechargeable. Thus these cells find potential use in rechargeable micropower sources and uninterrupted power supplies for microelectronic circuit devices.

Research paper thumbnail of Transport and dielectric studies on 66.6% Agl-22.2% Ag 2 O-11.1% ((1 − x )V 2 O 5 + x P 2 O 5 ) glassy electrolytes

Journal of Materials Science Letters, 1988

The quarternary glassy fast ion conducting compounds of the general formula MX-M20-XzOs-X~O5 wher... more The quarternary glassy fast ion conducting compounds of the general formula MX-M20-XzOs-X~O5 where M = Ag, Cu and Li; X, X' = V, As, P and Nb are of great interest as solid electrolyte materials for the various applications such as solid state batteries, analog memory devices, coulometer-timers, electrochemical capacitors and electrochromic displays . The preliminary investigation of the silver based AgI-Ag20-V2Os-PzO s quarternary system as a solid state battery material was reported . It was established that 66.6% Agi-22.2% Ag20-11.1% (0.8 V205 + 0.2 P205) glassy electrolyte has an ionic conductivity of 4.2 x 10 2I]-~cm-J and an electronic conductivity of 8.6 x 10-sf~-lcm-1 at room temperature. The criteria of choosing the same electrolyte for application to different solid state ionic devices necessitated the need to study the transport dielectric properties of mixtures of the formula 66.6% Agi-22.2% Ag20-11.1% ((1 -x)V205 + xP2Os) for 0.1 ~< x ~ 0.9. The complete study of ionic conductivity, electronic contribution to the total conductivity, behaviour of the dielectric constant, dielectric loss and loss tangent for the various compositions will provide the necessary data for choosing a particular composition for the required application. Hence glasses with different compositions for 0.1 ~< x <~ 0.9 were prepared and characterized by the transport and dielectric properties. The compositional dependence of the ionic and electronic conductivities and the dielectric constant, dielectric loss and the loss tangent were plotted in Figs 1 to 5 to analyse the nature of the semiconducting (1-x)V205 4-xP205 glasses and the superionic conducting 66.6%AgI-22.2%Ag~O-11.1%((1 -x) V205 + xP205) glasses. A detailed study of the time dependent, frequency dependent and the temperature dependent conductivities with an explanation of the conduction mechanism will be discussed elsewhere .

Research paper thumbnail of Transport and dielectric studies on silver based molybdo-tungstate quaternary superionic conducting glasses

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

Solid State Ionics, 1988

... Ceram. Soc. 50 (1967), p. 516. Full Text via CrossRef. U. Selvaraj and KJ Rao, J. Non Cryst. ... more ... Ceram. Soc. 50 (1967), p. 516. Full Text via CrossRef. U. Selvaraj and KJ Rao, J. Non Cryst. Solids 72 (1985), p. 315. Abstract | PDF (939 K) | View Record in Scopus | Cited By in Scopus (44). PSS Prasad and S. Radhakrishna, J. Non Cryst. Solids, submitted for publication. ...

Research paper thumbnail of Structural, thermal, and transport studies on silver vanadium phosphate solid electrolyte

Journal of Solid State Chemistry, 1988

Silver-based quarternary fast ion conducting polycrystalline and glassy materials have been prepa... more Silver-based quarternary fast ion conducting polycrystalline and glassy materials have been prepared by the open-air crucible melting method. A preliminary investigation revealed that the glassy electrolyte, when used in an electrochemical cell, has a high capacity of 15 mAH for the composition mole% 66.6 AgI22.2 Ag 2O-11.1 (0.8 V 2O 50.2 P 2O 5). In a further study, to establish the highest conducting composition, by varying the AgI mole%, it was found that the composition with mole% 70 AgI20 Ag 2O-10 (0.8 V 2O 50.2 P 2O 5) has an ionic conductivity of 8.2 × 10 -2 (ohm cm) -1 and an electronic conductivity of 2.6 × 10 -8 (ohm cm) -1 at 32°C. The infrared, far infrared, Raman, and EPR spectroscopic techniques were used to analyze and confirm the presence of ionic clusters, thus highlighting the structural units of the solid electrolyte. The existence of ionic clusters in the glass was assumed to be responsible for enhanced ionic conduction. Thermal and transport properties of the compound were studied to explore the effect of mixing two glass formers. The glass transition temperature ( Tg) obtained from the DTA technique was well correlated with the obtained glass transition temperature from the log σT vs{10 3}/{T} plot. The resistance-time and the resistance-frequency characteristics of the pellets were investigated to study the behavior of the material as an electrolyte in solid-state batteries.

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

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

Journal of Power Sources, 1989

Research paper thumbnail of Compositional dependent electrical conductivity in silver arsenate solid electrolytes

Journal of Materials Science Letters, 1990

Research work on silver based ternary solid electrolytes, for example, superionic conducting vitr... more Research work on silver based ternary solid electrolytes, for example, superionic conducting vitreous electrolytes with B203, PzOs, V205, CrO3, MoO 3 and WO3 as glass forming oxides, is actively in progress because of their inherent advantages over the polycrystalline solid electrolytes in light of their application to solid state ionic devices [1][2][3][4][5]. Until now, B203 was the only established glass forming oxide which satisfied the Zachariasen criteria for the formation of glasses. This states that M203 type of oxides form amorphous networks only if the metal atom M is small enough to permit the formation of oxygen polyhedra with face sharing of the metal cation [6]. In this context, silver based B203 vitreous electrolytes were found to possess relatively high glass transition temperatures with very high ionic conductivities at room temperature, which are attributed to the nature of the glass former (B203) itself. The variation of transport properties with different glass former (GF) to glass modifier (GM) ratio in the ternary system AgI-Ag20-B203 were well explained emphasizing the influence of GF (B203) to GM (Ag20) ratio role on the conduction characteristics [7]. Hence it is believed that glass formers that satisfy the classical criteria are the most suitable for the preparation of silver based vitreous electrolytes. Thus the search for new glass formers of the type M2O 3 has been initiated to obtain highly conducting stable vitreous solid electrolytes.

Research paper thumbnail of A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals

A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals

Physica Status Solidi B-basic Solid State Physics, 1991

The optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient ... more The optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient (300 K) and liquid nitrogen temperatures (80 K). From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for the Co2+ ions in the crystals. The splittings observed for the 4T2g(F) band in Co2+ at 80 K is explained as due to the spin—orbit interaction. The band positions are fitted with the four parameters: B = 960 cm−1, C = 3840 cm−1, Dq = 940, and γ = 550 at 300 K and B = 990 cm−1, C = 3960 cm−1, Dq = 940, and γ = 600 at 80 K. The polarized crystal spectra of Co2+ doped 3 CdSO4 · 8 H2O are recorded at 80 K and the three anisotropic bands observed near 8097, 14422, and 18692 cm−1 are presumed to be due to the spin allowed 4T1g(F) → 4T2g(F), 4T1g(F) → 4A2g(F), and 4T1g(F) → 4Tlg(P) transitions of substitutional Co2+ in 3CdSO4 · 8H2O. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole in nature.Die optischen Absorptionsspektren von Co2+ in 3 CdSO4 8 H2O-Einkristallen werden bei Umgebungstemperatur (300 K) und Temperaturen des flüssigen Stickstoffs (80 K) untersucht. Aus der Art und Lage der beobachteten Banden kann eine erfolgreiche Zuordnung unter der Annahme von Oktaedersymmetrie für die Co2+-Ionen in den Kristallen vorgenommen werden. Die für die 4T2g(F)-Bande in Co2+ bei 80 K beobachtete Aufspaltung wird durch Spin—Bahn-Wechselwirkung erklärt. Die Lagen der Banden werden mit vier Parameter: B = 960 cm−1, C = 3840 cm−1, Dq = 940 und γ = 550 bei 300 K und B = 990 cm−1, C = 3960 cm−1, Dq = 940 und γ = 600 bei 80 K angepaßt. Die Polarisationsspektren der Co2+-dotierten 3 CdSO4 · 8 H2O-Kristalle werden bei 80 K aufgenommen und die drei anisotropen Banden bei 8097, 14422 und 18692 cm−1 durch spin-erlaubte 4T1g(F) → 4T2g(F)-, 4T1g(F) → 4A2g(F)- und 4T1g(F) → 4T1g(P)-Übergänge von substituiertem Co2+ in 3 CdSO4 · 8 H2O erklärt. Die beobachtete Anisotropie zeigt, daß die 4T2g(F)-Bande größenteils magnetischen Dipolcharakter hat, während die anderen beiden elektrischen Dipolcharakter haben.

Research paper thumbnail of Mixed glass former effect in mol% 66.67 AgI24.66Ag2O-8.33((1-x)B2O3-xAs2O3) quaternary amorphous solid electrolytes

Mixed glass former effect in mol% 66.67 AgI24.66Ag2O-8.33((1-x)B2O3-xAs2O3) quaternary amorphous solid electrolytes

Solid State Communications, 1991

... in press). 9. P. Sathya Sainath Prasad, AN Durga Rani S. Radhakrishna, J. Phys. and Chem. of ... more ... in press). 9. P. Sathya Sainath Prasad, AN Durga Rani S. Radhakrishna, J. Phys. and Chem. of Glasses (1990) (submitted). 10.W. Kauzmann, Chem. Rev. 43, 219 (1948). CA Angell KJ Rao, J. Phys. Chem. 57, 470 (1972). P ...

Research paper thumbnail of Heat of transport and thermoelectric power studies in Agl-Ag 2 O-V 2 O 5 -P 2 O 5 quaternary amorphous solid electrolyte system

Journal of Materials Science Letters, 1990

Solid electrolytes, more popularly known as superiomc conductors, have been of recent interest no... more Solid electrolytes, more popularly known as superiomc conductors, have been of recent interest not only to technologists as potential materials in solid-state ionic devices, but also to physicists because of the intricate conduction mechanisms that are being proposed to explain the unusually high ionic conductivity in some of the recently studied amorphous solid electrolyte systems. Recently, many silver-ion conducting amorphous solid electrolyte systems were reported to possess very high ionic conductivity and low electronic conductivity at ambient temperature along with many of their inherent advantages over the polycrystalline solid electrolytes . Th e present work deals with the quaternary amorphous solid electrolyte system AgI-Ag20-V2Os-P205 in which two glass formers are utilized, in contrast with the one glass former utilized in the ternary systems AgI-Ag20-V205 and AgI-Ag2Os-P2Os. The prominent improvement in the conduction characteristics of quaternary amorphous solid electrolytes when compare d with the ternary ones has been reported by Us [4=6]. in the quaternary silver vanadium phosphate system XAgI-(1 -X){yAg20-z[(1 --x ) V 2 0 5 -x P 2 O s ] } , the three parameters X, z/y and x (the molar concentration of AgI; the glass former (GF) to glass modifier (GM) ratio; and the relative concentration of one of the glass formers, respectively) were proved to be the governing factors of the ionic conduction mechanism [4-6]. The role played by each constituent of the system in leading to the conduction mechanism and its correlation with the structural aspects were emphasized in our previous communications . In the ternary systems AgI-Ag20-V205 and AgI-Ag20-P2Os, it has been reported that high ionic conductivity could not be achieved when AgI is replaced by AgBr or AgC1, thus making the role of AgI more curious . Thus, in the present quaternary amorphous solid electrolyte system XAgI-(1 -X) [2Ag20-l(0.8V2Os-0.2P2Os)], keeping the parameters z/y and x constant at 0.5 and 0.2, respectively, the effect of AgI m o l % on the heat of transport (HT) and thermoelectric power (TEP) measurements is reported. Thermoelectric power measurement has many advantages based on the fact that it is a zero-current process which avoids the contact resistance measurement ambiguities. Moreover, TEP studies on silver superionic conductors are 284 simpler than on conventional ionic solids due to the fact that a large and constant concentration of silver ions is set in motion with a small temperature gradient. Choosing the electrodes is relatively easy, unlike in conventional alkali halide conductors where none of the alkali metals or halogens could be used as electrodes. The thermoelectric power measurements on the quaternary amorphous solid electrolytes also provide information regarding new transport parameters which may help further understanding and optimization of the ionic conductivity [10,. Solid electrolytes with the composition XAgI-(1 -X){ yAg20-z[(1 -x)V2Os-xP2Os]}, for 40 < X < 80mo1% and 0.1 < x < 0.9, were prepared from Analar grade chemicals AgI, Ag20 , V205 and P205 (BDH, India). The chemicals were weighed accurately to the desired composition and mixed in a mortar with a pestle. The mixture was loaded in a quartz crucible and the contents melted at 500°C for 4 h, occasionally followed by stirring. The homogeneous melt was rapidly quenched in a stream of liquid nitrogen such that the nucleation of crystallization did not occur. The thin, brittle glass flakes obtained were allowed to come up to the ambient temperature and were stored in a desiccator. Another set of the same samples in the bulk form was prepared by pouring the melt into stainless steel moulds kept at liquid nitrogen temperature.

Research paper thumbnail of Chromium centres in 3 CdSO4 · 8 H2O single crystals

Chromium centres in 3 CdSO4 · 8 H2O single crystals

Physica Status Solidi B-basic Solid State Physics, 1989

The optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at ... more The optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at 300 and 80 K; the crystal field transitions are assigned and the B, C, Dq parameters evaluated. Polarisation investigations are undertaken to establish the exact electric dipole transitions and the exact magnetic dipole transitions. Splitting of the bands (differences between the parallel and perpendicular polarised spectra) due to the non-cubic fields acting on the chromium (III) ion are not observed though two inequivalent cadmium atoms exist in the lattice. Also no lowering of symmetry is observed either from the low temperature spectra or the polarised spectra. Radiation damage studies are undertaken to study the mechanism of the formation of Cr3+ to Cr+ and the valence state effect on the electronic transitions. The effect of space charge compensating vacancies on the electronic transitions and its effect on the crystal field strength is studied using the radiation damage spectra. The formation of Cr+ from Cr3+ through Cr2+ is well explained. The theoretically calculated values coincide well with the experimentally observed values for the octahedral symmetry for both, Cr3+ and Cr+ ions in 3 CdSO4 · 8 H2O lattice.Die optisehen Absorptionsspektren von Cr3+-dotierten 3 CdSO4 · 8 H2O-Einkristallen werden bei 300 und 80 K aufgenommen, die Kristallfeld-Übergänge zugeordnet und die B-, C-, Dq-Parameter berechnet. Um die exakten elektrischen und exakten magnetischen Dipolübergänge festzustellen, werden Polarisationsuntersuchungen unternommen. Aufspaltung der Banden (Unterschiede zwischen den parallel und senkrecht polarisierten Spektren) infolge der nicht-kubischen Felder, die auf das Chrom(III)-Ion wirken, werden nicht beobachtet, obwohl zwei nichtäquivalente Kadmiumatome im Gitter vorhanden sind. Auch eine Erniedrigung der Symmetrie wird weder in den Niedertemperaturspektren noch in den polarisierten Spektren beobachtet. Untersuchungen des Strahlungsdamage werden durchgeführt, um den Mechanismus der Bildung von Cr3+ zu Cr+ sowic den Einfluß des Valenzzustandes auf den elektronischen Übergang zu untersuchen. Der Einfluß von raumladungskompensierenden Leerstellen auf die elektronischen Übergänge und deren Einfluß auf die Stärke des Kristallfeldes werden mittels Strahlungsdamagespektren untersucht. Die Cr+-Bildung aus Cr3+ über Cr2+ wird gut erklärt. Die theoretisch berechneten Werte stimmen gut mit den experimentell beobachteten Werten für die Oktaedersymmetrie sowohl für Cr3+- als auch für Cr+-Ionen in 3 CdSO4 · 8 H2O-Gittern überein.

Research paper thumbnail of Electrical conductivity, TEP and dielectric studies on mol% 66.6 Agl-22.2 Ag 2 O-11.1 (0.8 V 2 O 5 -0.2 P 2 O 5 ) electrolyte material for solid state batteries

Journal of Materials Science, 1988

In the superionic conducting quarternary system Agl-Ag2O-V2O5-P2O5, the best ionic conductivity w... more In the superionic conducting quarternary system Agl-Ag2O-V2O5-P2O5, the best ionic conductivity was obtained for the composition 66.6% Agl-33.3% (2Ag2O-1 (V2O5-P2O5)), when the GF/GM ratio was varied from 0.20 to 5.0. Then fixing the GF/GM ratio at 0.50, the ratio of the glass formers V2O5 and P2O5 were varied and the highest conducting composition was obtained as 66.6% Agl-22.2 Ag2O-11.1% (0.8 V2O5-0.2 P2O5). A preliminary investigation using this material in the form of an electrolyte in a solid state electrochemical cell is reported. The polycrystalline and amorphous compounds were prepared from the same melt, by open air crucible melting and the rapid quenching technique. The ionic conductivity for the best conducting polycrystalline (hence referred as 66VP82P) and amorphous (66VP82G) samples was obtained as 8.3 × 10−3 and 4.2 × 10−2 Ω−1 cm−1 respectively. The electronic conductivity of the order 10−10 Ω−1 cm−1 was observed for 66VP82G and 10−8 Ω−1 cm−1 for 66VP82P samples. Thermoelectric power studies revealed that the charge carriers are the Ag+ ions, with an activation energy of 0.288eV for 66VP82G, which correlated well with the activation energy obtained from the conductivity measurements. The dielectric constant, dielectric loss and the loss tangent were calculated for both polycrystalline and glassy 66VP82 material. It was observed that the dielectric loss is more for the glassy material than the polycrystalline material. Solid state galvanic cells with 66.6% Agl-22.2% Ag2O-11.1% V2O5, 66.6% Agl-22.2%-Ag2O-11.1% P2O5 and 66.6% Agl-22.2% Ag2O-11.1% (0.8 V2O5-0.2 P2O5) (coded as 66V, 66P and 66VP82 respectively) electrolytes were constructed. Both polycrystalline and amorphous electrolyte cells were fabricated for a comparative study and the polarization effects were observed to be negligible in amorphous cells. The variation of open circuit voltage with temperature was reported and the current discharge curves indicate that the 66VP82 material has higher current capacity with high current drain when compared to 66V and 66P cells.

Research paper thumbnail of Electrochemical studies on solid state cells with mol % 70AgI20Ag 2 O-10(0.8V 2 O 5 -0.2P 2 O 5 ) amorphous electrolyte and organic cathodes

Journal of Applied Electrochemistry, 1989

The highest conducting amorphous solid electrolyte composition (mol %) 70AgI-20Ag2O-10(0.8V2O5-0.... more The highest conducting amorphous solid electrolyte composition (mol %) 70AgI-20Ag2O-10(0.8V2O5-0.2P2O5) in the system AgI-Ag2O-V2O5-P2O5 was investigated as an electrolyte material for solid state cells with organic cathodes by studying the electrochemical properties. The variation of open circuit voltage (OCV) with temperature, current discharge and the load characteristics were determined for the cells with iodine, tetramethyl ammonium iodide and tetrabutyl ammonium iodide as cathode materials. The cell capacities were estimated from the load characteristic curves and, in general, the cells were found to have very good stability at low current discharges even at high temperatures. In addition, it was found that the silver on the working electrode is electrochemically active and can be oxidized to Ag+ ions, making the organic cathode cells rechargeable. Thus these cells find potential use in rechargeable micropower sources and uninterrupted power supplies for microelectronic circuit devices.

Research paper thumbnail of Transport and dielectric studies on 66.6% Agl-22.2% Ag 2 O-11.1% ((1 − x )V 2 O 5 + x P 2 O 5 ) glassy electrolytes

Journal of Materials Science Letters, 1988

The quarternary glassy fast ion conducting compounds of the general formula MX-M20-XzOs-X~O5 wher... more The quarternary glassy fast ion conducting compounds of the general formula MX-M20-XzOs-X~O5 where M = Ag, Cu and Li; X, X' = V, As, P and Nb are of great interest as solid electrolyte materials for the various applications such as solid state batteries, analog memory devices, coulometer-timers, electrochemical capacitors and electrochromic displays . The preliminary investigation of the silver based AgI-Ag20-V2Os-PzO s quarternary system as a solid state battery material was reported . It was established that 66.6% Agi-22.2% Ag20-11.1% (0.8 V205 + 0.2 P205) glassy electrolyte has an ionic conductivity of 4.2 x 10 2I]-~cm-J and an electronic conductivity of 8.6 x 10-sf~-lcm-1 at room temperature. The criteria of choosing the same electrolyte for application to different solid state ionic devices necessitated the need to study the transport dielectric properties of mixtures of the formula 66.6% Agi-22.2% Ag20-11.1% ((1 -x)V205 + xP2Os) for 0.1 ~< x ~ 0.9. The complete study of ionic conductivity, electronic contribution to the total conductivity, behaviour of the dielectric constant, dielectric loss and loss tangent for the various compositions will provide the necessary data for choosing a particular composition for the required application. Hence glasses with different compositions for 0.1 ~< x <~ 0.9 were prepared and characterized by the transport and dielectric properties. The compositional dependence of the ionic and electronic conductivities and the dielectric constant, dielectric loss and the loss tangent were plotted in Figs 1 to 5 to analyse the nature of the semiconducting (1-x)V205 4-xP205 glasses and the superionic conducting 66.6%AgI-22.2%Ag~O-11.1%((1 -x) V205 + xP205) glasses. A detailed study of the time dependent, frequency dependent and the temperature dependent conductivities with an explanation of the conduction mechanism will be discussed elsewhere .

Research paper thumbnail of Transport and dielectric studies on silver based molybdo-tungstate quaternary superionic conducting glasses

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

Solid State Ionics, 1988

... Ceram. Soc. 50 (1967), p. 516. Full Text via CrossRef. U. Selvaraj and KJ Rao, J. Non Cryst. ... more ... Ceram. Soc. 50 (1967), p. 516. Full Text via CrossRef. U. Selvaraj and KJ Rao, J. Non Cryst. Solids 72 (1985), p. 315. Abstract | PDF (939 K) | View Record in Scopus | Cited By in Scopus (44). PSS Prasad and S. Radhakrishna, J. Non Cryst. Solids, submitted for publication. ...

Research paper thumbnail of Structural, thermal, and transport studies on silver vanadium phosphate solid electrolyte

Journal of Solid State Chemistry, 1988

Silver-based quarternary fast ion conducting polycrystalline and glassy materials have been prepa... more Silver-based quarternary fast ion conducting polycrystalline and glassy materials have been prepared by the open-air crucible melting method. A preliminary investigation revealed that the glassy electrolyte, when used in an electrochemical cell, has a high capacity of 15 mAH for the composition mole% 66.6 AgI22.2 Ag 2O-11.1 (0.8 V 2O 50.2 P 2O 5). In a further study, to establish the highest conducting composition, by varying the AgI mole%, it was found that the composition with mole% 70 AgI20 Ag 2O-10 (0.8 V 2O 50.2 P 2O 5) has an ionic conductivity of 8.2 × 10 -2 (ohm cm) -1 and an electronic conductivity of 2.6 × 10 -8 (ohm cm) -1 at 32°C. The infrared, far infrared, Raman, and EPR spectroscopic techniques were used to analyze and confirm the presence of ionic clusters, thus highlighting the structural units of the solid electrolyte. The existence of ionic clusters in the glass was assumed to be responsible for enhanced ionic conduction. Thermal and transport properties of the compound were studied to explore the effect of mixing two glass formers. The glass transition temperature ( Tg) obtained from the DTA technique was well correlated with the obtained glass transition temperature from the log σT vs{10 3}/{T} plot. The resistance-time and the resistance-frequency characteristics of the pellets were investigated to study the behavior of the material as an electrolyte in solid-state batteries.

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

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

Journal of Power Sources, 1989

Research paper thumbnail of Compositional dependent electrical conductivity in silver arsenate solid electrolytes

Journal of Materials Science Letters, 1990

Research work on silver based ternary solid electrolytes, for example, superionic conducting vitr... more Research work on silver based ternary solid electrolytes, for example, superionic conducting vitreous electrolytes with B203, PzOs, V205, CrO3, MoO 3 and WO3 as glass forming oxides, is actively in progress because of their inherent advantages over the polycrystalline solid electrolytes in light of their application to solid state ionic devices [1][2][3][4][5]. Until now, B203 was the only established glass forming oxide which satisfied the Zachariasen criteria for the formation of glasses. This states that M203 type of oxides form amorphous networks only if the metal atom M is small enough to permit the formation of oxygen polyhedra with face sharing of the metal cation [6]. In this context, silver based B203 vitreous electrolytes were found to possess relatively high glass transition temperatures with very high ionic conductivities at room temperature, which are attributed to the nature of the glass former (B203) itself. The variation of transport properties with different glass former (GF) to glass modifier (GM) ratio in the ternary system AgI-Ag20-B203 were well explained emphasizing the influence of GF (B203) to GM (Ag20) ratio role on the conduction characteristics [7]. Hence it is believed that glass formers that satisfy the classical criteria are the most suitable for the preparation of silver based vitreous electrolytes. Thus the search for new glass formers of the type M2O 3 has been initiated to obtain highly conducting stable vitreous solid electrolytes.

Research paper thumbnail of A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals

A Study of Cobalt Centers in 3 CdSO4 · 8 H2O Single Crystals

Physica Status Solidi B-basic Solid State Physics, 1991

The optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient ... more The optical absorption spectra of Co2+ in 3 CdSO4 · 8 H2O single crystals are studied at ambient (300 K) and liquid nitrogen temperatures (80 K). From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for the Co2+ ions in the crystals. The splittings observed for the 4T2g(F) band in Co2+ at 80 K is explained as due to the spin—orbit interaction. The band positions are fitted with the four parameters: B = 960 cm−1, C = 3840 cm−1, Dq = 940, and γ = 550 at 300 K and B = 990 cm−1, C = 3960 cm−1, Dq = 940, and γ = 600 at 80 K. The polarized crystal spectra of Co2+ doped 3 CdSO4 · 8 H2O are recorded at 80 K and the three anisotropic bands observed near 8097, 14422, and 18692 cm−1 are presumed to be due to the spin allowed 4T1g(F) → 4T2g(F), 4T1g(F) → 4A2g(F), and 4T1g(F) → 4Tlg(P) transitions of substitutional Co2+ in 3CdSO4 · 8H2O. The observed anisotropy indicates that the 4T2g(F) band is largely magnetic dipole while the other two are electric dipole in nature.Die optischen Absorptionsspektren von Co2+ in 3 CdSO4 8 H2O-Einkristallen werden bei Umgebungstemperatur (300 K) und Temperaturen des flüssigen Stickstoffs (80 K) untersucht. Aus der Art und Lage der beobachteten Banden kann eine erfolgreiche Zuordnung unter der Annahme von Oktaedersymmetrie für die Co2+-Ionen in den Kristallen vorgenommen werden. Die für die 4T2g(F)-Bande in Co2+ bei 80 K beobachtete Aufspaltung wird durch Spin—Bahn-Wechselwirkung erklärt. Die Lagen der Banden werden mit vier Parameter: B = 960 cm−1, C = 3840 cm−1, Dq = 940 und γ = 550 bei 300 K und B = 990 cm−1, C = 3960 cm−1, Dq = 940 und γ = 600 bei 80 K angepaßt. Die Polarisationsspektren der Co2+-dotierten 3 CdSO4 · 8 H2O-Kristalle werden bei 80 K aufgenommen und die drei anisotropen Banden bei 8097, 14422 und 18692 cm−1 durch spin-erlaubte 4T1g(F) → 4T2g(F)-, 4T1g(F) → 4A2g(F)- und 4T1g(F) → 4T1g(P)-Übergänge von substituiertem Co2+ in 3 CdSO4 · 8 H2O erklärt. Die beobachtete Anisotropie zeigt, daß die 4T2g(F)-Bande größenteils magnetischen Dipolcharakter hat, während die anderen beiden elektrischen Dipolcharakter haben.

Research paper thumbnail of Mixed glass former effect in mol% 66.67 AgI24.66Ag2O-8.33((1-x)B2O3-xAs2O3) quaternary amorphous solid electrolytes

Mixed glass former effect in mol% 66.67 AgI24.66Ag2O-8.33((1-x)B2O3-xAs2O3) quaternary amorphous solid electrolytes

Solid State Communications, 1991

... in press). 9. P. Sathya Sainath Prasad, AN Durga Rani S. Radhakrishna, J. Phys. and Chem. of ... more ... in press). 9. P. Sathya Sainath Prasad, AN Durga Rani S. Radhakrishna, J. Phys. and Chem. of Glasses (1990) (submitted). 10.W. Kauzmann, Chem. Rev. 43, 219 (1948). CA Angell KJ Rao, J. Phys. Chem. 57, 470 (1972). P ...

Research paper thumbnail of Heat of transport and thermoelectric power studies in Agl-Ag 2 O-V 2 O 5 -P 2 O 5 quaternary amorphous solid electrolyte system

Journal of Materials Science Letters, 1990

Solid electrolytes, more popularly known as superiomc conductors, have been of recent interest no... more Solid electrolytes, more popularly known as superiomc conductors, have been of recent interest not only to technologists as potential materials in solid-state ionic devices, but also to physicists because of the intricate conduction mechanisms that are being proposed to explain the unusually high ionic conductivity in some of the recently studied amorphous solid electrolyte systems. Recently, many silver-ion conducting amorphous solid electrolyte systems were reported to possess very high ionic conductivity and low electronic conductivity at ambient temperature along with many of their inherent advantages over the polycrystalline solid electrolytes . Th e present work deals with the quaternary amorphous solid electrolyte system AgI-Ag20-V2Os-P205 in which two glass formers are utilized, in contrast with the one glass former utilized in the ternary systems AgI-Ag20-V205 and AgI-Ag2Os-P2Os. The prominent improvement in the conduction characteristics of quaternary amorphous solid electrolytes when compare d with the ternary ones has been reported by Us [4=6]. in the quaternary silver vanadium phosphate system XAgI-(1 -X){yAg20-z[(1 --x ) V 2 0 5 -x P 2 O s ] } , the three parameters X, z/y and x (the molar concentration of AgI; the glass former (GF) to glass modifier (GM) ratio; and the relative concentration of one of the glass formers, respectively) were proved to be the governing factors of the ionic conduction mechanism [4-6]. The role played by each constituent of the system in leading to the conduction mechanism and its correlation with the structural aspects were emphasized in our previous communications . In the ternary systems AgI-Ag20-V205 and AgI-Ag20-P2Os, it has been reported that high ionic conductivity could not be achieved when AgI is replaced by AgBr or AgC1, thus making the role of AgI more curious . Thus, in the present quaternary amorphous solid electrolyte system XAgI-(1 -X) [2Ag20-l(0.8V2Os-0.2P2Os)], keeping the parameters z/y and x constant at 0.5 and 0.2, respectively, the effect of AgI m o l % on the heat of transport (HT) and thermoelectric power (TEP) measurements is reported. Thermoelectric power measurement has many advantages based on the fact that it is a zero-current process which avoids the contact resistance measurement ambiguities. Moreover, TEP studies on silver superionic conductors are 284 simpler than on conventional ionic solids due to the fact that a large and constant concentration of silver ions is set in motion with a small temperature gradient. Choosing the electrodes is relatively easy, unlike in conventional alkali halide conductors where none of the alkali metals or halogens could be used as electrodes. The thermoelectric power measurements on the quaternary amorphous solid electrolytes also provide information regarding new transport parameters which may help further understanding and optimization of the ionic conductivity [10,. Solid electrolytes with the composition XAgI-(1 -X){ yAg20-z[(1 -x)V2Os-xP2Os]}, for 40 < X < 80mo1% and 0.1 < x < 0.9, were prepared from Analar grade chemicals AgI, Ag20 , V205 and P205 (BDH, India). The chemicals were weighed accurately to the desired composition and mixed in a mortar with a pestle. The mixture was loaded in a quartz crucible and the contents melted at 500°C for 4 h, occasionally followed by stirring. The homogeneous melt was rapidly quenched in a stream of liquid nitrogen such that the nucleation of crystallization did not occur. The thin, brittle glass flakes obtained were allowed to come up to the ambient temperature and were stored in a desiccator. Another set of the same samples in the bulk form was prepared by pouring the melt into stainless steel moulds kept at liquid nitrogen temperature.

Research paper thumbnail of Chromium centres in 3 CdSO4 · 8 H2O single crystals

Chromium centres in 3 CdSO4 · 8 H2O single crystals

Physica Status Solidi B-basic Solid State Physics, 1989

The optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at ... more The optical absorption spectra of 3 CdSO4 · 8 H2O single crystals doped with Cr3+ is recorded at 300 and 80 K; the crystal field transitions are assigned and the B, C, Dq parameters evaluated. Polarisation investigations are undertaken to establish the exact electric dipole transitions and the exact magnetic dipole transitions. Splitting of the bands (differences between the parallel and perpendicular polarised spectra) due to the non-cubic fields acting on the chromium (III) ion are not observed though two inequivalent cadmium atoms exist in the lattice. Also no lowering of symmetry is observed either from the low temperature spectra or the polarised spectra. Radiation damage studies are undertaken to study the mechanism of the formation of Cr3+ to Cr+ and the valence state effect on the electronic transitions. The effect of space charge compensating vacancies on the electronic transitions and its effect on the crystal field strength is studied using the radiation damage spectra. The formation of Cr+ from Cr3+ through Cr2+ is well explained. The theoretically calculated values coincide well with the experimentally observed values for the octahedral symmetry for both, Cr3+ and Cr+ ions in 3 CdSO4 · 8 H2O lattice.Die optisehen Absorptionsspektren von Cr3+-dotierten 3 CdSO4 · 8 H2O-Einkristallen werden bei 300 und 80 K aufgenommen, die Kristallfeld-Übergänge zugeordnet und die B-, C-, Dq-Parameter berechnet. Um die exakten elektrischen und exakten magnetischen Dipolübergänge festzustellen, werden Polarisationsuntersuchungen unternommen. Aufspaltung der Banden (Unterschiede zwischen den parallel und senkrecht polarisierten Spektren) infolge der nicht-kubischen Felder, die auf das Chrom(III)-Ion wirken, werden nicht beobachtet, obwohl zwei nichtäquivalente Kadmiumatome im Gitter vorhanden sind. Auch eine Erniedrigung der Symmetrie wird weder in den Niedertemperaturspektren noch in den polarisierten Spektren beobachtet. Untersuchungen des Strahlungsdamage werden durchgeführt, um den Mechanismus der Bildung von Cr3+ zu Cr+ sowic den Einfluß des Valenzzustandes auf den elektronischen Übergang zu untersuchen. Der Einfluß von raumladungskompensierenden Leerstellen auf die elektronischen Übergänge und deren Einfluß auf die Stärke des Kristallfeldes werden mittels Strahlungsdamagespektren untersucht. Die Cr+-Bildung aus Cr3+ über Cr2+ wird gut erklärt. Die theoretisch berechneten Werte stimmen gut mit den experimentell beobachteten Werten für die Oktaedersymmetrie sowohl für Cr3+- als auch für Cr+-Ionen in 3 CdSO4 · 8 H2O-Gittern überein.