Investigation of size-driven phase transition in bismuth titanate nanocrystals by Raman spectroscopy

Phonon properties of nanosized bismuth layered ferroelectric material—Bi2WO6

“…[15] In case of Bi 4 Ti 3 O 12 , which undergoes a phase transition at 675 • C for the bulk material, the structure changed from orthorhombic to tetragonal at a critical size of 44 nm. [16] These results show that it is plausible to attribute the observed changes in the Raman and IR spectra of Bi 2 WO 6 to diminishing P2 1 ab distortion. Our low-temperature results and the previous high-temperature studies of polycrystalline Bi 2 WO 6 show that, when this distortion decreases with increasing temperature (tilt of the WO 6 octahedra about the pseudo-tetragonal axis decreases), the separation between the 789 and 850-815 cm −1 Raman bands decreases and the relative intensity of the Raman bands observed at 286 and 265 cm −1 (at 7 K) decreases.…”

“…[15,16] It has been shown that the phase-transition temperature decreased with decreasing size of crystallites for SrBi 2 Ta 2 O 9 and Bi 4 Ti 3 O 12 . [15,16] In the first case, this decrease was relatively weak and the structure changed from orthorhombic to tetragonal for crystallites smaller than 6-7 nm. [15] In case of Bi 4 Ti 3 O 12 , which undergoes a phase transition at 675 • C for the bulk material, the structure changed from orthorhombic to tetragonal at a critical size of 44 nm.…”

“…Interestingly, the former studies of Bi 4 Ti 3 O 12 also showed a very strong intensity decrease of the A 1g mode for this Aurivillius compound, especially pronounced for the crystallites smaller than 30 nm. [16] This behavior was attributed to a size-induced phase transition from the orthorhombic to tetragonal symmetry. [16] However, since the temperature-dependent studies of Bi 4 Ti 3 O 12 showed that no significant changes in intensity of this band should be observed due to the phase transition, [35] the intensity decrease observed in Ref.…”

“…[16] This behavior was attributed to a size-induced phase transition from the orthorhombic to tetragonal symmetry. [16] However, since the temperature-dependent studies of Bi 4 Ti 3 O 12 showed that no significant changes in intensity of this band should be observed due to the phase transition, [35] the intensity decrease observed in Ref. [16] is most likely also due to plate-like nature of the synthesized nanocrystals.…”

“…[15,16] This disappearance was attributed to size-induced phase transition into the paraelectric tetragonal phase. [15,16] Although a number of papers have been published reporting the synthesis of nanocrystalline Bi 2 WO 6 , no attempt has been made to investigate the dependence of the structure and phonon properties on the crystallite size. We have decided, therefore, to perform such studies for this material.…”