UC San Diego

This thesis mainly focused on investigating the suitable synthesis methods to get barium titanate (BaTiO3) and strontium titanate (SrTiO3) nanocubes without using any capping agents. Two synthesis methods (hydrothermal and molten-salt) were used to synthesize BaTiO3 and SrTiO3 nanoparticles. X-ray diffraction (XRD) was used to identify phases and determine the phase purity of synthesized BaTiO3 and SrTiO3 nanoparticles. The morphology and formation mechanisms were investigated through scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was verified that BaTiO3 nanocubes can be successfully synthesized by molten-salt method, while SrTiO3 nanocubes were obtained by hydrothermal method. The synthesized nanocubes for both materials have high crystallinity and high purity.The formation mechanism of BaTiO3 nanocubes was proposed due to the low surface energy of {100} crystal planes. Crystal planes with low surface energy are preferred in the crystal growth stage. The formation of SrTiO3 nanocubes was proposed due to the crystal growth of {100} crystal planes and face-to-face attachment. These mechanisms provided clear explanations for the formation of BaTiO3 and SrTiO3 nanocubes without using any capping agents, which can be applied to other metal oxide nanocubes. Future studies can be focused on the synthesis of other metal oxide nanocubes by using the formation mechanisms proposed in this thesis.