Activity of SrO in La1-xSrxMnO3-y (x=0.065, 0.10, 0.15 or 0.20) by a solidstate EMF method

Thermodynamic activity of SrO, a(SrO), in lanthanum manganite doped with Sr O with the stoichiometry La1-xSrxMnO3-y (where x=0.065, 0.10, 0.15 or 0.20) was measured as a function of temperature over the range of similar to 750 -1000 K by employing an EMF technique with CaF2 or SrF2 as the fluoride ion conducting electrolyte under an atmosphere of oxygen at unit fugacity. Whe n Pt/SrO,SrF2,O-2 was used as the reference electrode for the test electrod e Pt/0.15 LSM, SrF2,O-2, sintered SrF2 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 DeltaG(SrO), log a( SrO) and the corresponding activity coefficients (gamma (SrO)) for the four solid solutions were determined and log a(SrO) was found to exhibit decrea sing negative deviation from ideality with increasing SrO content. The Delt aG(SrO) for these compositions could be represented as -4.81-0.03360T (K) f or 0.065 LSM, -5.68-0.02818T for 0.10 LSM, -9.84-0.01950T for 0.15 LSM and -11.42-0.01360T for 0.20 LSM in terms of kJ mol(-1). (C) 2001 Elsevier Scie nce B.V. All rights reserved.