Phase relation in BaBiO 3− x by coulometric titration

Abstract

The electromotive force (EMF) of the solid electrolyte galvanic cell: Pt, O 2(BaBiO 3− x )|YSZ|O 2(air), Pt has been measured in the temperature range of 975–1300 K. The oxygen content in BaBiO 3− x was controlled by coulometric titration. The relative partial molar free energy of oxygen (Δ [ovbar|G] o2) was determinedfrom the EMF. Three distinct phases (I, II and III) were observed for 0≦ x<0.5. The relative partial molar enthalpy (Δ[ovbar|H] o2) and entropy (Δ[ovbar|S] o2) of oxygen were calculated from the temperature dependence of the Δ[ovbar|G] o2. The value of Δ[ovbar|H] o2 decreased in phase I and increased in phase II with an increase in x. In phase II, the change of Δ[ovbar|S] o2 agreed well with that of the configurational entropy, Δ[ovbar|S] o2(conf), which was calculated assuming the following defect reaction: 1 2 O 2 + V .. O + Bi X O + Bi .. Bi .