Anisotropy in morphology and crystal structure of BaTiO3 nanoblocks

• BaTiO3 nanocubes and nanocuboids were synthesized by the hydrothermal method.
• The percentage of BaTiO3 nanocuboids showed a size-dependent characteristic.
• The crystalline phases of BaTiO3 nanoblocks possess both tetragonal and cubic phases.
• The formation of BaTiO3 nanocuboids was attributed to the tetragonal phase and the lattice strain.

Single crystalline {100} dominant BaTiO3 nanoblocks were synthesized by the hydrothermal method using aqueous sources of Ba and Ti, and organic additives. BaTiO3 nanoblocks with neat surface and standard corner angle show two kinds of morphology, cubic and cuboid shapes. Based on TEM images of BaTiO3 nanoblocks, the percentage of nanocuboids improved from 24.3% to 51.8%, as the average size of nanoblocks varied from ~ 15 nm to ~ 25 nm. The asymmetric morphology of BaTiO3 nanocuboids reveals an anisotropic growth pattern. One straightforward method was employed to discuss the crystal phase of BaTiO3 nanocuboids by using the HR-TEM images and the corresponding FFT patterns. The d spacing of {100} crystal planes show diverse values. The ratios of d spacing of (100) crystal plane and the perpendicular (001) plane are larger than one. The short edge direction in BaTiO3 nanocuboids coincides with their [001] crystal orientation. According to the enlarged FFT filtered HR-TEM images, the shape and oriented array of the unit cells in nanocuboids played a crucial role on the formation of anisotropy in morphology. Co-considering the DSC result, the findings indicate the existence possibility of tetragonal phase in BaTiO3 nanocuboids with < 30 nm size.

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