• T R N Kutty

      Articles written in Journal of Chemical Sciences

    • Hydrothermal phase equilibria in Er2O3−H2O−CO2 and Tm2O3−H2O−CO2 systems

      Iftiqhar Mohamed J A K Tareen T R N Kutty

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      Isobaric phase equilibria in Er2O3−H2O−CO2 and Tm2O3−H2O−CO2 systems have been determined at 650 and 1300 bars and temperature range of 100–800°C. The equilibria depend on the mole fraction of CO2 in the coexisting fluid. The stable phases: Ln(OH)3, Ln2(CO3)33H2O, Ln(OH)CO3-orthorhombic, Ln2O2CO3-hexagonal, LnOOH and Ln2O3-cubic are common to both the systems. Additional phases observed in the thulium system are Tm2O(OH)2CO3 and Tm6(OH)4(CO3)7. Two other phases isolated are Tm6O2(OH)8(CO3)3 and Tm4(OH)6(CO3)3 which are stabilised only in the presence of alkali impurities. Stability field of Ln(OH)3 is limited to$$X_{CO_2 }< 0 \cdot 01$$.Tm(OH)CO3 does not stabilise at low$$X_{CO_2 } $$; therefore TmOOH coexists with all the phases other than Tm6(OH)4(CO3)7. When$$X_{CO_2 } = 1$$, the stable phases are Tm2O2CO3 and Tm2O3 in the order of increasing temperature. The normal carbonate, Tm2(CO3)3·8H2O has no stability at higher pressures.

    • Behaviour of acceptor states in semiconducting BaTiO3 and SrTiO3

      T R N Kutty

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      The semiconductivity inMTiO3 (M=Ba, Sr) in the temperature range of practical applications is greatly influenced by the electronic charge redistribution among the acceptor states, arising from the frozen cation vacancies as well as the transition metal ion impurities. The conductivity measurements and defect chemistry investigations above 800 K indicate that the predominant lattice defects areM− and oxygen vacancies. There is dominantp-type conduction at higherPO2 values in acceptor doped materials at high temperatures. However, they are insulating solids around room temperature due to the redistribution of electrons between the neutral, singly-or doubly-ionised acceptor states. Results fromepr and resistivity measurements show that the above charge redistribution is dependent on crystal structure changes. Hence the electron or hole loss by the acceptor states is influenced by the soft modes which also accounts for the differences in electrical properties of BaTiO3 and SrTiO3. The results are also useful in explaining the positive temperature coefficient in resistance and some photo-electrochemcial properties of these solids.

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