Measurement of Gibbs energy of formation of LaGaO3 using a composition-graded solid electrolyte

A composition-graded solid electrolyte (LaF3)(y).(CaF2)(1-y) was used for t he measurement of the standard Gibbs energy of formation of LaGaO3, from it s component oxides, An equimolar mixture of CaO and CaF2 was employed as th e reference electrode. The composition of the working electrode depended on temperature. A three-phase mixture of LaGaO3 + Ga2O3 + LaF3 was used in th e temperature range from 910 to 1010 K, while a mixture of LaGaO3 + Ga2O3 LaO1-xF1+2x was employed from 1010 to 1170 K, Both the reference and worki ng electrodes were placed under pure oxygen gas. Because of the high activi ty of LaF3 at the working electrode, there was significant diffusion of LaF 3 into CaF2. The composition-graded electrolyte was designed to minimize th e electrode-electrolyte interaction. The concentration of LaF3 varied acros s the solid electrolyte; from y = 0 near the reference electrode to a maxim um value y = 0.32 at the working electrode. Far the correct interpretation of the electromotive force at T > 1010 K, it was necessary to use thermodyn amic properties of the lanthanum oxyfluoride solid solution. The standard G ibbs energy of formation of LaGaO3, from its component oxides according to the reaction, 1/2La(2)O(3) (A-rare earth) + 1/2Ga(2)O(3) (beta) --> LaGaO3 (rhombohedral) can be represented by the equation: DeltaG(f,(ox))(o)/J mol( -1) = -46 230 + 7.75 T/K (+/-1500).