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تسجيل مستخدم جديدMacro- and microscopic properties of strontium doped indium oxide
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Solid state synthesis and physical mechanisms of electrical conductivity variation in polycrystalline, strontium doped indium oxide In2O3:(SrO)x were investigated for materials with different doping levels at different temperatures (T=20-300 C) and ambient atmosphere content including humidity and low pressure. Gas sensing ability of these compounds as well as the sample resistance appeared to increase by 4 and 8 orders of the magnitude, respectively, with the doping level increase from zero up to x=10%. The conductance variation due to doping is explained by two mechanisms: acceptor-like electrical activity of Sr as a point defect and appearance of an additional phase of SrIn2O4. An unusual property of high level (x=10%) doped samples is a possibility of extraordinarily large and fast oxygen exchange with ambient atmosphere at not very high temperatures (100-200 C). This peculiarity is explained by friable structure of crystallite surface. Friable structure provides relatively fast transition of samples from high to low resistive state at the expense of high conductance of the near surface layer of the grains. Microscopic study of the electro-diffusion process at the surface of oxygen deficient samples allowed estimation of the diffusion coefficient of oxygen vacancies in the friable surface layer at room temperature as 3x10^(-13) cm^2/s, which is by one order of the magnitude smaller than that known for amorphous indium oxide films.
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N.I. Matskevich (Nikolaev Institute of Inorganic Chemistry
, Siberiann Branch of the Russian Academy of Sciences
, Novosibirsk
2005
The standard molar enthalpy of formation of SrY0.05Ce0.95O2.975 has been derived by combining the enthalpy of solution of this compound in 1 M HCl + 0.1 KI obtained by us and auxiliary literature data. The following value has been derived: DfH (SrY0.
05Ce0.95O2.975, s, 298.15 K) = -1720.4 (3.4) kJ/mol. The obtained value has been used to obtain the formation enthalpy of SrY0.05Ce0.95O2.975 from the mixture of binary oxides (DoxH (298.15 K) = -45.9 (3.4) kJ/mol) and formation enthalpy of reaction of SrY0.05Ce0.95O2.975 with water forming Sr(OH)2, CeO2, Y2O3 (DrH (298.15 K) = -85.5 (3.4) kJ/mol). Data obtained by solution calorimetry and additional information on the entropies of different substances have shown that SrY0.05Ce0.95O2.975 is thermodynamically stable with respect to a mixture of SrO, Y2O3, CeO2 and that the reaction of SrY0.05Ce0.95O2.975 with water is thermodynamically favourable.
The dissolution enthalpies of BaCe0.7Ho0.2In0.1O2.85 and BaCe0.7Sm0.2In0.1O2.85 were measured by method of solution calorimetry in 1M hydrochloric acid with adding 0.1 M KI. The obtained data were compared with earlier measured data on dissolution en
thalpies of BaCe0.7Nd0.2In0.1O2.85, BaCe0.7Gd0.2In0.1O2.85. The dependence of dissolution enthalpies from lanthanide radius was constructed. As was shown the relationship is not linear.
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