Hydrothermal Synthesis of Nanocrystalline Barium Cerate Using Hexamethylenetetramine

Abstract

Barium cerate is a candidate material for use in solid-oxide fuel cells (SOFC) and other solid-state ionic devices, due to its high proton conductivity in reduced-temperature operating conditions. The present paper investigates the crystal structure, surface and grain morphologies, particle size and distribution, and microstructural defects of both as-synthesized and heat-treated nanoparticles of barium cerate. Crystalline barium cerate was successfully synthesized in nanoparticle form using a relatively low-temperature wet chemistry route using hexamethylenetetramine. X-ray diffraction was carried out to understand the formation of various phases at different stages of processing. The evolution of the morphology and both the size and the shape of nanoparticles, were studied by high-resolution transmission electron microscopy after different heat-treatment temperatures. Nanoparticles are found to exhibit a cubic morphology after synthesis at 80°C, and change to a mixed multi-faceted and equiaxed morphology as annealing temperature is increased to 800°C. Crystallographically oriented surface steps can be observed at the surrounding edges of nanoparticles. Microstructural features, including edge dislocation and low-angle grain boundaries, are observed in some nanoparticles. Possible mechanisms for nanoparticle formation and the effect of annealing temperature on morphological changes are discussed.