Synthesis of SrAl4O7 via citric acid precursor

SrAl4O7 was synthesized by Pechini method using citric acid as a chelating agent and ethylene glycol as an esterification agent. 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 SrAl4O7 were investigated. Increasing the pH of the starting solutions and the molar ratio of citric acid to total metal cations concentration promoted the formation of SrAl4O7. When the molar ratio of citric acid to total metal cations concentration was 2, well crystallized, single-phase SrAl4O7 was synthesized at 900 °C for 2 h for the precursor with pH 7, but it could not be obtained for the precursor with pH 1. Increasing the molar ratio of citric acid to total metal cations concentration up to 4, single-phase SrAl4O7 was also synthesized at 900 °C for 2 h for the precursors with pH 7, but it was obtained at 1100 °C for 2 h for the precursors with pH 1. The stability of SrAl4O7 as a function of time and temperature was determined. We found that SrAl4O7 can be stable up to 1400 °C for 2 h and it shows decomposition at 1500 °C for 2 h. Heating single-phase SrAl4O7 powder at 1600 °C for 2 h, most of SrAl4O7 decomposes to SrAl12O19 as the major phase and an unidentified phase (main reflection at d = 3.0149). DSC, TG, FT-IR and XRD were used to characterize the precursors and the derived oxide powders.