Synthesis of BaCeO3 powders by a fast aqueous citrate–nitrate process

A fast aqueous citrate–nitrate process has been successfully used to prepare the stoichiometric BaCeO3 powders. It was found that an optimal amount of water added in the mixing process of barium nitrate, cerium nitrate, and citric acid is helpful on the formation of a clear gel that was subsequently formed by the condensation of added diethylene glycol monomers at room temperature. The gel was heated to an easily handled precursor in a powder form at 400 °C for 1 h. The precursors were characterized by X-ray powder diffraction (XRD), differential thermal analysis (DTA), thermal gravimetric analysis (TGA), thermal mechanical analysis (TMA), Fourier transform infrared spectrometry (FTIR), and scanning electron microscopy (SEM). The phase evolution from the precursor to the desired BaCeO3 powders by XRD and FTIR revealed that the presence of BaCO3 is a complex problem in this process. A high-temperature trigonal BaCO3 intermediate was found between 800 °C and 1000 °C by the in-situ X-ray powder diffraction experiments. The phase purity of the formed BaCeO3 powders may be more properly identified by FTIR instead of XRD because of the amorphous feature of the carbonate phase. The TMA revealed that at 1100 °C part of the precursor crystallized to needle-shaped BaCeO3 crystals accompanied by a small expansion, which is also related to the presence of BaCO3 in the precursor, and this can be removed by a preheating treatment of the precursor at 900 °C for 4 h.