Morphology and atomic-scale surface structure of barium titanate nanocrystals formed at hydrothermal conditions

BaTiO3 (BT) nanocrystals were synthesized by a hydrothermal method at 220 °C, and their crystal structure, morphology, and surface structure were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution TEM (HRTEM), respectively. The results of XRD and Raman spectroscopy indicated that the BT nanocrystals are of tetragonal phase at room temperature. SEM and TEM images showed that the larger Ba/Ti molar ratios in the precursors led to the formation of larger nanocrystals with a cubic morphology. HRTEM images revealed that the cubic nanocrystals were bound by their {1 0 0} faces. A core–shell surface structure was observed in the nanocrystals, where the shell layer was cubic with a thickness in the range 2–3.5 nm, and the core was a bulk tetragonal. The interface structure between the shell and the core was coherent without any interfacial dislocation. At rough edges of the nanocrystals, their {1 1 0} edges were faceted by {1 0 0} planes in a form of few atomic layers wide steps, showing some degree of ledge-kink reconstruction. These microstructural results enable ones to achieve nanocrystals with controlled size and morphology.