Effects of pH and citric acid contents on the synthesis of BaTi4O9 via polymeric precursor

BaTi4O9 was synthesized via polymeric precursor made of citric acid and ethylene glycol. The effects of the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration on the formation of BaTi4O9 were investigated. Increasing the pH of the starting solutions retarded the formation of BaTi4O9, but the increase of the molar ratio of citric acid to total metal cations concentration enhanced the formation of BaTi4O9. Single-phase BaTi4O9 was obtained at 1100 °C for 2 h when the molar ratio of citric acid to total metal cations concentration was unity, independent of the pH of the starting solutions. Increasing the molar ratio of citric acid to total metal cations concentration up to 2, single-phase BaTi4O9 was synthesized at 1000 °C for 2 h for the pH unadjusted precursors, but for the precursors with pH 6.0, the formation temperature of single-phase BaTi4O9 was increased to 1100 °C. When the molar ratio of citric acid to total metal cations concentration was increased further up to 4, single-phase BaTi4O9 formed at 1000 °C for 2 h for the precursors with or without pH adjustment. DSC, TG, XRD and FESEM were used to characterize the precursors and the derived oxide powders. Details of the synthesis and characterizations of the resultant products were given.