A composition-graded solid electrolyte (LaF3)y · (CaF2)1-y was used for the measurement of the standard Gibbs energy of formation of LaGaO3 from its component oxides. An equimolar mixture of CaO and CaF2 was employed as the reference electrode. The composition of the working electrode depended on temperature. A three-phase mixture of LaGaO3 + Ga2O3 + LaF3 was used in the 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 working electrodes were placed under pure oxygen gas. Because of the high activity of LaF3 at the working electrode, there was significant diffusion of LaF3 into CaF2. The composition-graded electrolyte was designed to minimize the electrode–electrolyte interaction. The concentration of LaF3 varied across the solid electrolyte; from y = 0 near the reference electrode to a maximum value y = 0.32 at the working electrode. For the correct interpretation of the electromotive force at T > 1010 K, it was necessary to use thermodynamic properties of the lanthanum oxyfluoride solid solution. The standard Gibbs energy of formation of LaGaO3 from its component oxides according to the reaction, ½La2O3 (A-rare earth) + ½Ga2O3 (b) → LaGaO3 (rhombohedral) can be represented by the equation: δGo f,(ox) /J mol -1 = –46 230 + 7.75 T/K (±1500).
使用成分分级固体电解质 (LaF3)y - (CaF2)1-y 测量了 LaGaO3 由其成分氧化物形成的标准吉布斯能。参比电极采用 CaO 和 CaF2 的等摩尔混合物。工作电极的成分取决于温度。在 910 至 1010 K 的温度范围内使用的是 LaGaO3 + Ga2O3 + LaF3 的三相混合物,而在 1010 至 1170 K 的温度范围内使用的是 LaGaO3 + Ga2O3 + LaO1-xF1+2x 的混合物。由于工作电极上的 LaF3 活性很高,LaF3 向 CaF2 的扩散量很大。设计成分分级的电解质是为了尽量减少电极与电解质之间的相互作用。LaF3 的浓度在整个固体电解质中变化;从参比电极附近的 y = 0 到工作电极处的最大值 y = 0.32。为了正确解释 T > 1010 K 时的电动势,有必要使用氟化镧固溶体的热力学特性。按照 ½La2O3 (A-rare earth) + ½Ga2O3 (b) → LaGaO3 (rhombohedral) 的反应,LaGaO3 由其氧化物组分形成的标准吉布斯能可用公式表示:δGo f,(ox) /J mol -1 = -46 230 + 7.75 T/K (±1500) 。