Thermal Stability of the Perovskite BaBiO3

Thermal stability of the perovskite BaBiO3 and phase relations in the BaO–BiO1.5(BiO2.5) system in the range of 45–55 mol%. BiO1.5 at p(O2)=0.21 atm have been studied by thermogravimetric analysis, differential thermal analysis, X-ray diffraction, chemical analysis, and transmission electron microscopy. It has been found that BaBiO3 loses oxygen in the temperature range between 600 and 1015°C with formation of the oxygen-deficient phases BaBiO2.88, BaBiO2.83, BaBiO2.75, and BaBiO2.55. BaBiO3 and the oxygen-deficient phases form two-phase regions involving phases of the perovskite series BamBim+nOy at the Bi-rich side and Bam+nBimOy at the Ba-rich side. At 1015°C the BaBiO2.55 phase exhibits incongruent melting. At further increasing temperature the 1:1 (Ba:Bi) sample passes through a sequence of the crystallization fields of the Ba-rich phases of the compositions 5:4, 4:3, 3:2, 9:5, and 17:9, reaching the complete melting state at 1100°C.