Browsing by Author "West, A.R."

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    New Li+-ion conductors, Li4 ? 2xTi1 ?xSxO4, based on the Li4TiO4 structure
    (Journal of Materials Chemistry, 1994) Dissanayake, M.A.K.L.; Sumathipala, H.H.; West, A.R.
    In the system Li4TiO4?Li2SO4, a wide range of solid solutions, Li4 ? 2xSxTi1 ?xO4(0 < x < 0.2) with Li4TiO4 structure is formed. The ionic conductivity increases with x and exhibits a maximum (bulk) value of 8.30 ? 10?6 S cm?1at 27 �C with an activation energy of 0.51 eV for x= 0.2. The enhancement in conductivity is associated with an increase in concentration of lithium-ion vacancies, created via the mechanism 2Li++ Ti4+ S6+, but is attributable specifically to a decrease in activation energy for conduction. This is the first report of high Li+-ion conductivity in the Li4TiO4structural family.
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    New solid electrolytes and mixed conductors: Li3 + xCr1 ? xMxO4: M = Ge, Ti
    (Solid State Ionics, 1995) Dissanayake, M.A.K.L.; Gunawardane, R.P.; Sumathipala, H.H.; West, A.R.
    New Li+ ion conducting solid solutions with ?-LISICON type structure have been found in the system Li3 + xCr1 ? xGexO4 for 0.35 < x < 0.92. Conductivity increases with x; at x = 0.90, ? (bulk) ? 1.4 ? 10?5 S cm?1 at 27 �C rising to 0.044 S cm?1 at 300 �C; Ea = 0.51 eV. Similar ? solid solutions form in the Ti system, Li3 + xCr1 ? xTixO4: 0.5 < x <0.8; however, these are mixed Li+ ion and electronic conductors. Both systems are unusual in containing Cr in the +V oxidation state.
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    Novel Li+ Ion Conductors and Mixed Conductors, Li3+xSixCr1-xO4 and a Simple Method for Estimating Li+/e- Transport Numbers.
    (Chem Inform, 1995) Sumathipala, H.H.; Dissanayake, M.A.K.L.; West, A.R.
    ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a ?Full Text? option. The original article is trackable via the ?References? option.
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    Novel LISICON mixed conductors, Li4 ? 2xCoxGeO4
    (Solid State Ionics, 1996) Sumathipala, H.H.; Dissanayake, M.A.K.L.; West, A.R.
    A novel LISICON type ? solid solution range has been found in the system Li4 ? 2xCoxGeO4 for 0.15 ? x ? 0.8. The highest net conductivity, 8.4 ? 10?6Scm?1, was observed for x = 0.25 at 27 �C rising to 3.35 ? 10?3Scm?1 at 300 �C with an activation energy of 0.71 eV. A charge/discharge polarisation technique was used to investigate the transference number of these materials. Results corroborate those obtained by low frequency a.c. impedance measurements and show the occurrence of mixed Li+ ion and electronic conductivity. The relative amounts of each vary with composition; x = 0.25 has both the highest conductivity and the highest ionic transference number, 0.19.
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    Synthesis and properties of a new ? polymorph of Li3CrO4
    (Journal of Materials Chemistry, 1994) Dissanayake, M.A.K.L.; Garcia-Martin, S.; Saez-Puche, R.; Sumathipala, H.H.; West, A.R.
    ?-Li3CrO4, isostructural with ?-Li3PO4, has been synthesized by two routes. Reaction of Li2CO3 and Cr2O3 in a 5 : 1 mole ratio in flowing Ar at 800 �C yields ?-Li3CrO4, with a small amount of Li2O. The Li2CO3, seems to have two functions. It is an essential reactant and acts as a novel oxidant, promoting conversion of CrIII to CrV. Reaction of Li2CO3 and CrO3 in a 3 : 1 mole ratio in flowing Ar also gives phase-pure ?-Li3CrO4. Magnetic measurements show Curie?Weiss behaviour in the range 20?300 K with a magnetic moment of 1.70 �B consistent with CrV in tetrahedral coordination. Conductivity measurements show a modest level of electronic conduction.