The effect of reducing gas mixture, H2-N2 or CO-N2, on the cubic-hexagonal transition in BaTiO3 has been investigated by X-ray diffraction, ESR, ESCA, PAS and chemical analysis. The firing temperatures of BaTiO3 were 1380°C and 1500°C, and the transition temperature in air is already known to be 1460°C. The fractional conversion to the hexagonal phase increased with increasing concentrations of reducing gases, larger for samples fired in H2-N2 than those fired in CO-N2 for the same concentrations of the reducing gases. The hexagonal phase in all samples increased proportionally to the amount of Ti3+ produced by reduction of Ti4+ ions, regardless of the reducing gas species and firing temperatures. It was found that the minimum amount of Ti3+ ions to stabilize the hexagonal BaTiO3 at room temperature was 0.3% of total Ti ions. ESCA spectra due to Ti3+ were observed in the sample fired in 100% H2 at 1380°C.
