Activity of SrO in La 1− xSr xMnO 3− y ( x=0.065, 0.10, 0.15 or 0.20) by a solid state EMF method

Abstract

Thermodynamic activity of SrO, a SrO, in lanthanum manganite doped with SrO with the stoichiometry La 1− x Sr x MnO 3− y (where x=0.065, 0.10, 0.15 or 0.20) was measured as a function of temperature over the range of ∼750–1000 K by employing an EMF technique with CaF 2 or SrF 2 as the fluoride ion conducting electrolyte under an atmosphere of oxygen at unit fugacity. When Pt/SrO,SrF 2,O 2 was used as the reference electrode for the test electrode Pt/0.15 LSM, SrF 2,O 2, sintered SrF 2 was used as the electrolyte. In all other galvanic cells, both the test and reference electrodes contained LSM with different dopant concentrations. The SrO potential ΔG SrO, log a SrO and the corresponding activity coefficients ( γ SrO) for the four solid solutions were determined and log a SrO was found to exhibit decreasing negative deviation from ideality with increasing SrO content. The ΔG SrO for these compositions could be represented as −4.81–0.03360 T (K) for 0.065 LSM, −5.68–0.02818 T for 0.10 LSM, −9.84–0.01950 T for 0.15 LSM and −11.42–0.01360 T for 0.20 LSM in terms of kJ mol −1.