Ultraviolet Raman Spectroscopy Of Cube-Shaped Barium Titanate Nanocrystals Of Variable Sizes

Barium titanate (BaTiO ₃ ) cube- shaped nanocrystals of various sizes (8, 10, 15, and 20 nm) were analyzed using variable- temperature Raman spectroscopy. The nanocrystals were synthesized by thermal decomposition of metal fatty salts under hydrothermal conditions by our collaborators, the group of G. Caruntu (Central Michigan University). Ultraviolet excitation by a 325 nm helium- cadmium laser produced spectra measured from 10 to 500 K. The spectra of the BaTiO ₃ bulk single crystal were measured for comparison. The temperature dependence of Raman spectra analysis allowed us to determine that the BaTiO ₃ nanocrystals behaved differently than the BaTiO ₃ bulk single crystal; they did not exhibit the phase transformations characteristic of the bulk material with increasing temperature. All the nanocrystals studied were ferroelectric at low temperatures; the ferroelectric phase transition temperature was determined from the temperature evolution of Raman spectra as a function of the nanocrystals size.