Sarath Bandaranayake - Academia.edu (original) (raw)

Papers by Sarath Bandaranayake

Vingnanam Journal of Science

Montmorillonite (MMT) is naturally occurring clay mineral in Sri Lanka. It is an aluminosilicate ... more Montmorillonite (MMT) is naturally occurring clay mineral in Sri Lanka. It is an aluminosilicate crystalline compound with layered structure. In this structure an octahedral sheet of aluminum-oxygen (Al-O) is sandwiched between two tetrahedral sheets of silicon-oxygen (Si-O). The MMT structure can accommodate various monovalent and divalent cations such as H + , Li + , Na + , Mg 2+ within the interlayer spacing. Natural Li-MMT and Na-MMT are found in various parts of the world. The MMT structure has an ability to exchange interlayer cations with various other divalent cations. MMT with interlayer alkali cations show appreciable ionic conductivity. Natural Na-MMT found in Sri Lanka was used for the present study. To improve the ionic conductivity of natural Na-MMT, the structure was further saturated with Na + ions. The Na + ion concentration of saturated Na-MMT was measured by Inductive Couple Plasma Mass Spectroscopy. The structural and electrical properties of Na saturated MMT were characterized by SEM and Complex Impedance Spectroscopy. As a result of Na+ ion saturation the bulk conductivity of Na-MMT was increased to 3.41×10-4 S cm-1 at 30  C. Saturated Na-MMT has negligible electronic conductivity which is less than 0.001%. For using Na-MMT as intercalation cathode materials in rechargeable batteries, an appreciable electronic conductivity must also be present. To enhance the electronic conductivity of saturated Na-MMT, carbon black was mixed. The electronic transference number of saturated Na-MMT pellets was measured by the DC polarization technique. The electronic transference number of saturated Na-MMT with 25% and 30% carbon black were 0.81 and 0.87 respectively.

Solid State Ionics, 2006

ABSTRACT Glasses in the 3TeO2xLi2O(1−x)V2O5 system have been synthesised for 0≤x≤1. Conductivity ... more ABSTRACT Glasses in the 3TeO2xLi2O(1−x)V2O5 system have been synthesised for 0≤x≤1. Conductivity data obey an Arrhenius type behaviour between room temperature and the glass transition temperature. The isothermal conductivity curves exhibit a sharp minimum near x=0.5. Values of activation energies and pre-exponential factors in the V2O5 rich region are lower compared to those in the alkali oxide rich region implying that the conductivity mechanisms in these two regions are different. Experimental values suggest that an electronic conductivity by polaron hopping between VVI and VV cations would prevail in the first region. In the alkali oxide rich region, ionic conductivity would operate by an interstitial pair mechanism between non-bridging oxygens. The very low conductivity expected for x=0.5 could be explained by assuming that, for this composition, both ionic and electronic paths would not percolate any more.

All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.

Global Journal of Science & Engineering, 2020

Anthill clay is a distinct soil/clay genre among common soil types because of the stockpiling met... more Anthill clay is a distinct soil/clay genre among common soil types because of the stockpiling method. The small particles are carried in and erected an anthill by a small creature that it is called as termite. In generally, clay is a conspicuous raw material for industrial applications greatly and the assay of expediencies of anthill clay for advanced material applications were the prospects of the existing research. Carefully collected anthill clay samples were characterized under the physically and chemically using standard procedures and instruments. The mechanical characteristics of prepared bricks from anthill clays under 8000C were investigated. As the major outcomes of the existing investigation of raw clays, there were looked to 5.56 of PH value, 15% of natural moisture content, gap graded and symmetrically distributed arrangement of grains, 60% finer particle percentage (<0.075mm) according to the weight, composition of Fe, Ti, Ba and K based compounds including Fe miner...

Physics and Chemistry of Glasses

Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic press... more Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic pressure (1×10−4–0·5 GPa) have been performed on ionic conductive, xP2O5–(1–x)Na2O, sodium phosphate glasses and on electronic conductive, xP2O5–(1–x)V2O5, phosphovanadate glasses with x=0·4 and 0·5. Isobaric variations for ionic conductivity with temperature are characteristic of an activated mechanism for charge carrier formation and migration. The associated activation enthalpy, ΔH * (around 0·7 eV), is found to be pressure independent. A low activation entropy, ΔS *, is found to decrease with increasing pressure. Isothermal logarithmic variations of the ionic conductivity as a function of pressure are linear with negative slopes. A positive ‘activation volume’, ΔV * (mean value of around 5 cm3 mol−1) is calculated from these slopes. Its increase with temperature can be thermodynamically correlated to a diminution of the activation entropy with pressure. Isobaric conductivity variations of...

Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and Kahatagaha-Kolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types

Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006

The performances of gamma-MnO2 cathode in alkaline battery depend on the crystallochemical proper... more The performances of gamma-MnO2 cathode in alkaline battery depend on the crystallochemical properties of MnO2 as well as of graphite used to improve electronic conductivity of the cathode mixture. In the present work we have studied the performances of Sri Lanka natural graphite in the reduction process of gamma-MnO2 and compare it with the other synthetic and natural graphites. We

Solid State Ionics - Materials and Devices - Proceedings of the 7th Asian Conference, 2000

Solid State Ionics - Trends in the New Millennium - Proceedings of the 8th Asian Conference, 2002

A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhi... more A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO9:Cu(CF5SO3)2 made by complexing copper triflate (CuTf2) with PEO appears to show scientifically intriguing transport properties. Although copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the

Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006

Sri Lanka natural vein graphite has various morphologies with different structural and physical c... more Sri Lanka natural vein graphite has various morphologies with different structural and physical characteristics. The identified most abundant morphology, the shiny-slippery-fibrous (SSI) graphite found in two mines, Bogala and Kahatagaha-Kolongaha, has a very high purity over 98% and high crystallinity. The characterization of Li-graphite intercalation process was mainly performed with the initial discharge-charge profiles at the current rate of C/20

Solid State Ionics, 1990

Abstract Electrical conductivity of different compositions of the Li 2 SO 4 -Li 2 WO 4 binary sys... more Abstract Electrical conductivity of different compositions of the Li 2 SO 4 -Li 2 WO 4 binary system has been measured below 500°C using complex impedance technique. Conductivity isotherms at various temperatures exhibit two maxima, one at 34 mole% Li 2 WO 4 composition and the other at 70 mole% Li 2 WO 4 composition. The maximum conductivity observed at 34 mole% Li 2 WO 4 composition has been attributed to the composite effect resulting from the interfacial conductivity in the finely dispersed grains in the two-phase eutectic mixture. The maximum conductivity observed at 70 mole% Li 2 WO 4 near the solid solubility limit in the Li 2 WO 4 based solid solution region has been attributed to the availability of more interstitial space for Li-ion migration, as a result of the replacement of larger W by smaller S atoms.

Solid State Ionics, 1990

Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measu... more Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measurements have been performed for the Na2S0.,-MgSO, binary system. The redetermined phase diagram shows that the solid solution of the high-temperature phase of Na*SO, is stable up to 35 mol% MgSO, at 680°C. The ionic conductivity in this phase increases rapidly with increasing MgSO, content, the maximum conductivity at 540°C is about 150 times larger than the conductivity of pure Na2S0,. For two intermediate compounds, Na2Mg(S04)2 and Na2Mg3(S04)4, the ionic conductivity is relatively low, 2x 10m4 and 4X 10-6fi-1 cm-' at 500°C.

Solid State Ionics, 1988

... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) ... more ... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) 699. [ 3l ] BN Mehrotra, Z. Kristallogr. 155 (1981) 159. [ 32 ] C). Toft Sorensen, Gh, Johannnesen and K. Clausen, in: Transport structure relations in fast ion and mixed conductors, eds. ...

Solid State Ionics, 1995

Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.

Solid State Ionics, 1992

Lithium sulphate and a few other compounds have high temperature phases which are both solid elec... more Lithium sulphate and a few other compounds have high temperature phases which are both solid electrolytes and plastic crystals (rotor phases). Three types of experiments are here considered in order to test the validity ofa "paddie-wheei mechanism" that has been proposed for cation conductivity in these phases. A single-crystal neutron diffraction study has been performed for cubic lithium sulphate. The refinement of the data gives a very complex model for the location of the lithium ions. There is definitely a void at and near the octahedrai (1/2, 1/2, 1/2) position. 90% of the lithium ions are located at the tetrahedral 8c-sites (1/4, 1/4, 1/4), although significantly distorted in the directions of the four neighbouring sulphate ions. The remaining 10% of the lithium ions are termed as an evenly distributed spherical shell which is surrounding the sulphate ions. The lithium ions are transported along a slightly curved pathway of continuous lithium occupation corresponding to a distance of about 3.7 A. Thus, lithium transport occurs in one of the six directions [ 110 ], [ 1 i0 ], [ 101 ] etc. The electrical conductivity has been studied for solid solutions of lithium tungstate in cubic lithium sulphate. The conductivity is reduced in the one-phase region, while it is increased in a two phase (solid-melt) region. There are pronounced differences between the rotor phases and other phases concerning how partial cation substitution affects the electrical conductivity of solid solutions. Regarding self and interdiffnsion, all studied mono-and divalent cations are very mobile in the rotor phases, which lack the pronounced correlation with ionic radii that is characteristic for diffusion in other classes of solid electrolytes. The quoted studies are to be considered as strong evidence against a percolation model proposed by Secco.

Solid State Ionics, 1991

Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.

Solid State Ionics, 1996

Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all c... more Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques

Solid State Ionics, 1995

Glasses in the x NazO(1-n)TeO, system have been synthesized for 0.18 IX I 0.33. Glass transition ... more Glasses in the x NazO(1-n)TeO, system have been synthesized for 0.18 IX I 0.33. Glass transition temperature and density data are reported as a function of X. In the glass forming region, ionic conductivity spreads over two orders of magnitude at 200°C when the total concentration of sodium cations varies only by a factor of two. Conductivity data obey an Arrhenius type behaviour with a same pre exponential term in agreement with an interstitial mechanism for ion transport.

Physical Chemistry Chemical Physics, 2002

ABSTRACT

Materials Research Bulletin, 2004

Magnesium ion containing gel polymer electrolytes based on polyacrylonitrile (PAN) have been synt... more Magnesium ion containing gel polymer electrolytes based on polyacrylonitrile (PAN) have been synthesized and characterized using ac impedance measurements. The electrolyte composition having the highest room temperature conductivity was found by varying the ratios ...

Vingnanam Journal of Science

Montmorillonite (MMT) is naturally occurring clay mineral in Sri Lanka. It is an aluminosilicate ... more Montmorillonite (MMT) is naturally occurring clay mineral in Sri Lanka. It is an aluminosilicate crystalline compound with layered structure. In this structure an octahedral sheet of aluminum-oxygen (Al-O) is sandwiched between two tetrahedral sheets of silicon-oxygen (Si-O). The MMT structure can accommodate various monovalent and divalent cations such as H + , Li + , Na + , Mg 2+ within the interlayer spacing. Natural Li-MMT and Na-MMT are found in various parts of the world. The MMT structure has an ability to exchange interlayer cations with various other divalent cations. MMT with interlayer alkali cations show appreciable ionic conductivity. Natural Na-MMT found in Sri Lanka was used for the present study. To improve the ionic conductivity of natural Na-MMT, the structure was further saturated with Na + ions. The Na + ion concentration of saturated Na-MMT was measured by Inductive Couple Plasma Mass Spectroscopy. The structural and electrical properties of Na saturated MMT were characterized by SEM and Complex Impedance Spectroscopy. As a result of Na+ ion saturation the bulk conductivity of Na-MMT was increased to 3.41×10-4 S cm-1 at 30  C. Saturated Na-MMT has negligible electronic conductivity which is less than 0.001%. For using Na-MMT as intercalation cathode materials in rechargeable batteries, an appreciable electronic conductivity must also be present. To enhance the electronic conductivity of saturated Na-MMT, carbon black was mixed. The electronic transference number of saturated Na-MMT pellets was measured by the DC polarization technique. The electronic transference number of saturated Na-MMT with 25% and 30% carbon black were 0.81 and 0.87 respectively.

Solid State Ionics, 2006

ABSTRACT Glasses in the 3TeO2xLi2O(1−x)V2O5 system have been synthesised for 0≤x≤1. Conductivity ... more ABSTRACT Glasses in the 3TeO2xLi2O(1−x)V2O5 system have been synthesised for 0≤x≤1. Conductivity data obey an Arrhenius type behaviour between room temperature and the glass transition temperature. The isothermal conductivity curves exhibit a sharp minimum near x=0.5. Values of activation energies and pre-exponential factors in the V2O5 rich region are lower compared to those in the alkali oxide rich region implying that the conductivity mechanisms in these two regions are different. Experimental values suggest that an electronic conductivity by polaron hopping between VVI and VV cations would prevail in the first region. In the alkali oxide rich region, ionic conductivity would operate by an interstitial pair mechanism between non-bridging oxygens. The very low conductivity expected for x=0.5 could be explained by assuming that, for this composition, both ionic and electronic paths would not percolate any more.

All in-text references underlined in blue are linked to publications on ResearchGate, letting you... more All in-text references underlined in blue are linked to publications on ResearchGate, letting you access and read them immediately.

Global Journal of Science & Engineering, 2020

Anthill clay is a distinct soil/clay genre among common soil types because of the stockpiling met... more Anthill clay is a distinct soil/clay genre among common soil types because of the stockpiling method. The small particles are carried in and erected an anthill by a small creature that it is called as termite. In generally, clay is a conspicuous raw material for industrial applications greatly and the assay of expediencies of anthill clay for advanced material applications were the prospects of the existing research. Carefully collected anthill clay samples were characterized under the physically and chemically using standard procedures and instruments. The mechanical characteristics of prepared bricks from anthill clays under 8000C were investigated. As the major outcomes of the existing investigation of raw clays, there were looked to 5.56 of PH value, 15% of natural moisture content, gap graded and symmetrically distributed arrangement of grains, 60% finer particle percentage (<0.075mm) according to the weight, composition of Fe, Ti, Ba and K based compounds including Fe miner...

Physics and Chemistry of Glasses

Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic press... more Accurate conductivity measurements, as a function of temperature (30–120°C) and hydrostatic pressure (1×10−4–0·5 GPa) have been performed on ionic conductive, xP2O5–(1–x)Na2O, sodium phosphate glasses and on electronic conductive, xP2O5–(1–x)V2O5, phosphovanadate glasses with x=0·4 and 0·5. Isobaric variations for ionic conductivity with temperature are characteristic of an activated mechanism for charge carrier formation and migration. The associated activation enthalpy, ΔH * (around 0·7 eV), is found to be pressure independent. A low activation entropy, ΔS *, is found to decrease with increasing pressure. Isothermal logarithmic variations of the ionic conductivity as a function of pressure are linear with negative slopes. A positive ‘activation volume’, ΔV * (mean value of around 5 cm3 mol−1) is calculated from these slopes. Its increase with temperature can be thermodynamically correlated to a diminution of the activation entropy with pressure. Isobaric conductivity variations of...

Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morpho... more Graphite Intercalation Compounds (GIC) with HNO 3 were chemically obtained using different morphologies of natural graphite from Sri Lanka, Madagascar and Krömful. X-ray powder patterns of the products showed the formation of second stage GIC (HNO 3). These compounds were used to produce exfoliated graphite at 550°C in air. The expansion ratio was measured and compared with different types of natural expanded graphite. Accordingly, the pellet type Madagascar graphite and Kahatagaha-Kolongaha shiny, slippery, fibrous graphite (KSSI; one of the morphology of natural graphite of Sri Lanka) showed the greatest volumes of expansion. The samples with the largest average particle sizes had the largest expansion volumes, which can be explained by the proportionality between structural, morphological and textural characteristics of expanded and raw graphite types

Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006

The performances of gamma-MnO2 cathode in alkaline battery depend on the crystallochemical proper... more The performances of gamma-MnO2 cathode in alkaline battery depend on the crystallochemical properties of MnO2 as well as of graphite used to improve electronic conductivity of the cathode mixture. In the present work we have studied the performances of Sri Lanka natural graphite in the reduction process of gamma-MnO2 and compare it with the other synthetic and natural graphites. We

Solid State Ionics - Materials and Devices - Proceedings of the 7th Asian Conference, 2000

Solid State Ionics - Trends in the New Millennium - Proceedings of the 8th Asian Conference, 2002

A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhi... more A number of Cu++ ion conducting, poly(ethylene oxide) (PEO) based solid polymer electrolytes exhibit interesting electrochemical properties. In particular, the polymer electrolyte PEO9:Cu(CF5SO3)2 made by complexing copper triflate (CuTf2) with PEO appears to show scientifically intriguing transport properties. Although copper ion transport in these systems has been seen from plating stripping processes, the detailed mechanism of ionic transport and the

Solid State Ionics - Advanced Materials for Emerging Technologies - Proceedings of the 10th Asian Conference, 2006

Sri Lanka natural vein graphite has various morphologies with different structural and physical c... more Sri Lanka natural vein graphite has various morphologies with different structural and physical characteristics. The identified most abundant morphology, the shiny-slippery-fibrous (SSI) graphite found in two mines, Bogala and Kahatagaha-Kolongaha, has a very high purity over 98% and high crystallinity. The characterization of Li-graphite intercalation process was mainly performed with the initial discharge-charge profiles at the current rate of C/20

Solid State Ionics, 1990

Abstract Electrical conductivity of different compositions of the Li 2 SO 4 -Li 2 WO 4 binary sys... more Abstract Electrical conductivity of different compositions of the Li 2 SO 4 -Li 2 WO 4 binary system has been measured below 500°C using complex impedance technique. Conductivity isotherms at various temperatures exhibit two maxima, one at 34 mole% Li 2 WO 4 composition and the other at 70 mole% Li 2 WO 4 composition. The maximum conductivity observed at 34 mole% Li 2 WO 4 composition has been attributed to the composite effect resulting from the interfacial conductivity in the finely dispersed grains in the two-phase eutectic mixture. The maximum conductivity observed at 70 mole% Li 2 WO 4 near the solid solubility limit in the Li 2 WO 4 based solid solution region has been attributed to the availability of more interstitial space for Li-ion migration, as a result of the replacement of larger W by smaller S atoms.

Solid State Ionics, 1990

Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measu... more Differential scanning calorimetry, X-ray diffractrometry and complex impedance spectroscopy measurements have been performed for the Na2S0.,-MgSO, binary system. The redetermined phase diagram shows that the solid solution of the high-temperature phase of Na*SO, is stable up to 35 mol% MgSO, at 680°C. The ionic conductivity in this phase increases rapidly with increasing MgSO, content, the maximum conductivity at 540°C is about 150 times larger than the conductivity of pure Na2S0,. For two intermediate compounds, Na2Mg(S04)2 and Na2Mg3(S04)4, the ionic conductivity is relatively low, 2x 10m4 and 4X 10-6fi-1 cm-' at 500°C.

Solid State Ionics, 1988

... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) ... more ... 43 (1981) 398. [ 30 ] F. ElKabbany, Y. Badr and T. Tosson, Phys. Status Solidi (a) 63 (1981) 699. [ 3l ] BN Mehrotra, Z. Kristallogr. 155 (1981) 159. [ 32 ] C). Toft Sorensen, Gh, Johannnesen and K. Clausen, in: Transport structure relations in fast ion and mixed conductors, eds. ...

Solid State Ionics, 1995

Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra... more Ionic conductivity of Li+ conducting glasses with a macromolecular network made of PO, tetrahedra and TeO, bipyramids have been measured. Glass pellets, according to the formula 0.4Li,O-0.6[ xP,O,-(1-x)Te,O,] were obtained by room temperature quench~g of melts in a brass mould. The glass forming domain was limited to 0.4 IX s 0.8 and the glass transition temperatures were between 240°C and 320°C. Ionic conductivities below Tg obey Arrhenius relationships with an almost constant pre-exponential factor A with a value of log A (S K cm-') = 4.3 + 0.6. At constant temperature conductivity increases with x and a peak is observed at x = 0.6.

Solid State Ionics, 1992

Lithium sulphate and a few other compounds have high temperature phases which are both solid elec... more Lithium sulphate and a few other compounds have high temperature phases which are both solid electrolytes and plastic crystals (rotor phases). Three types of experiments are here considered in order to test the validity ofa "paddie-wheei mechanism" that has been proposed for cation conductivity in these phases. A single-crystal neutron diffraction study has been performed for cubic lithium sulphate. The refinement of the data gives a very complex model for the location of the lithium ions. There is definitely a void at and near the octahedrai (1/2, 1/2, 1/2) position. 90% of the lithium ions are located at the tetrahedral 8c-sites (1/4, 1/4, 1/4), although significantly distorted in the directions of the four neighbouring sulphate ions. The remaining 10% of the lithium ions are termed as an evenly distributed spherical shell which is surrounding the sulphate ions. The lithium ions are transported along a slightly curved pathway of continuous lithium occupation corresponding to a distance of about 3.7 A. Thus, lithium transport occurs in one of the six directions [ 110 ], [ 1 i0 ], [ 101 ] etc. The electrical conductivity has been studied for solid solutions of lithium tungstate in cubic lithium sulphate. The conductivity is reduced in the one-phase region, while it is increased in a two phase (solid-melt) region. There are pronounced differences between the rotor phases and other phases concerning how partial cation substitution affects the electrical conductivity of solid solutions. Regarding self and interdiffnsion, all studied mono-and divalent cations are very mobile in the rotor phases, which lack the pronounced correlation with ionic radii that is characteristic for diffusion in other classes of solid electrolytes. The quoted studies are to be considered as strong evidence against a percolation model proposed by Secco.

Solid State Ionics, 1991

Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary ... more Ionic conductivity of a-Li2SO4 with up to 4 mol% Li2WO4 has been measured using quartz capillary U-tubes and complex impedance technique. A significant drop in conductivity and increase in activation energy is observed for 2, 2.5, 3 and 3.5 mol% Li2WO4 compositions while 4 tool% LizWO4 composition shows an increased conductivity. Based on a recent phase diagram of the binary system, the results are interpreted as convincing evidence for the "'Paddle Wheel" mechanism of ion transport in ct-Li2SO4.

Solid State Ionics, 1996

Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all c... more Glasses in the binary system xNa2P2O6-(l − x)Na2Te2O5 have been synthesised for 0≤x ≤1. For all compositions, the glasses are transparent and appear homogeneous. Nevertheless for compositions near x = 0.4 glasses seem to be heterogeneous on SEM observations. Glass transition temperatures for all the compositions are between 220 and 310 °C. Conductivity data have been obtained using impedance techniques

Solid State Ionics, 1995

Glasses in the x NazO(1-n)TeO, system have been synthesized for 0.18 IX I 0.33. Glass transition ... more Glasses in the x NazO(1-n)TeO, system have been synthesized for 0.18 IX I 0.33. Glass transition temperature and density data are reported as a function of X. In the glass forming region, ionic conductivity spreads over two orders of magnitude at 200°C when the total concentration of sodium cations varies only by a factor of two. Conductivity data obey an Arrhenius type behaviour with a same pre exponential term in agreement with an interstitial mechanism for ion transport.

Physical Chemistry Chemical Physics, 2002

ABSTRACT

Materials Research Bulletin, 2004

Magnesium ion containing gel polymer electrolytes based on polyacrylonitrile (PAN) have been synt... more Magnesium ion containing gel polymer electrolytes based on polyacrylonitrile (PAN) have been synthesized and characterized using ac impedance measurements. The electrolyte composition having the highest room temperature conductivity was found by varying the ratios ...