Thermal analysis and phase evolution of nanocrystalline perovskite oxide materials synthesized via hydrothermal and self-combustion methods

Nanocrystalline perovskite oxide materials ABO₃ (where A = Ba, Ca, Mg, Sr; and B = Ce, Mn, and Ti) have been synthesized via sol-citrate combustion and hydrothermal-based methods with and without surfactant under mild conditions. Metal-titanates (ATiO₃) were prepared using synthesized anatase-TiO₂ nanotube powder, metal hydroxide/chloride solutions, and NaOH as raw materials. The stoichiometric amount of all reactants were put in polytetrafluoroethylene (PTFE)-lined stainless steel digestion reactor and were kept in convention oven at desired reaction conditions like mole composition, pH, temperature, and time, in range A/Ti = 0.9–1.1, 10–12, 150–170 °C for 24–48 h, respectively. The nanocrystalline barium cerium oxide (BaCeO₃) was synthesized using citric acid as polymerization agent in sol-combustion process, whereas barium manganite (BaMnO₃) was prepared via hydrothermal process using polyethyl glycol surfactant as structure directing agent. Thermal stability, phase evolution, and morphology of synthesized products were characterized by thermogravimetry and differential thermal analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). XRD results revealed that synthesized CaTiO₃ and BaMnO₃ nanorods had an orthorhombic perovskite and hexagonal structure, respectively; whereas, the nanoparticle morphologies of BaTiO₃, Ba_0.5Sr_0.5TiO₃, and MgTiO₃, BaCeO₃ perovskite oxides were found strongly depended on pH of the precursor solutions. SEM images showed variety of morphological structures ranging from nanostructured surface with distinct particles morphology to nanowires and nanorods (length varies from nano to several micrometers) and uniform diameter ~<100 nm, depending upon the hydrothermal reaction conditions.