Temperature-dependent Raman spectroscopy of BaTiO_3 nanorods synthesized by using a template-assisted sol-gel procedure

摘要

In the present work, multiphase polycrystalline BTO nanorods were synthesized using template-assisted sol-gel deposition and their structural evolution was studied using thermo Raman spectroscopy, X-ray diffractometry and high-resolution transmission electron microscopy (HRTEM). In the BTO nanorods, the tetragonal phase was the dominant one, while both Raman and HRTEM indicated a coexistence with the high-temperature hexagonal polymorph. This phase was stable across the whole of the investigated temperature range (from -95 °C to 200 °C). The investigated nanorods underwent a diffuse phase transition from tetragonal to cubic with respect to the temperature, whereas the final phase-transition temperature was shifted to higher values compared to that expected for BTO. The low-temperature orthorhombic-to-rhombohedral phase transition was also shifted to higher temperatures. These differences could be explained by the strain induced by the presence of hexagonal nanolamellas intergrown within the tetragonal nanocrystals. This result indicates that the temperature of the ferroelectric phase transition in polycrystalline BTO nanorods can be manipulated by introducing a stable hexagonal phase.