Synthesis of Nanoparticles of Barium Lanthanum Hafnium Oxide by a Modified Combustion Process

Barium lanthanum hafnium oxide, a complex perovskite ceramic, has been synthesized as nanoparticles by a modified combustion process for the first time. The Ba, La, and Hf ions required for the formation of Ba₂LaHfO_5.5 were obtained in solution by dissolving in boiling nitric acid a stoichiometric mixture of BaCO₃, La₂O₃, and HfO₂ that had been heated at 1200 °C for 4 h. By complexing the ions with citric acid and using ammonia as fuel, it was possible to get Ba₂LaHfO_5.5 as nanoparticles in a single-step combustion process. The powder obtained by the present combustion process was characterized by X-ray diffraction, BET surface area analysis, differential thermal analysis, thermogravimetric analysis, infrared spectroscopy, and scanning and high-resolution transmission electron microscopy. According to the results of X-ray and electron diffraction, the powder synthesized through the combustion process showed single-phase barium lanthanum hafnium oxide. The transmission electron microscopic investigations showed a grain size of 42 nm, with a standard deviation of 8 nm. The nanoparticles of Ba₂LaHfO_5.5 synthesized by the present combustion technique could be sintered to >97% of the theoretical density at a relatively low temperature of 1425 °C. Scanning electron microscopic studies on the sintered Ba₂LaHfO_5.5 samples showed that the final grain size of the sintered specimen was <500 nm.