Vibrational spectra of three-component BaTiO3SrTiO3CaTiO3 short-period superlattices grown by pulsed laser deposition with atomic-layer control have been investigated by ultraviolet Raman spectroscopy. Monitoring the intensity of the first-order phonon peaks in Raman spectra as a function of temperature allowed determination of the ferroelectric phase transition temperature, Tc. Raman spectra indicate that all superlattices remain in the tetragonal ferroelectric phase with out-of-plane polarization in the entire temperature range below Tc. The dependence of Tc on the relative thicknesses of ferroelectric (BaTiO3) to non-ferroelectric materials (SrTiO3 and CaTiO3) has been studied. The highest Tc was found in superlattices having the largest relative amount of BaTiO3, provided that the superlattice maintains its coherency with the substrate. Strain relaxation leads to a significant decrease in the ferroelectric phase transition temperature.
Tenne, Dmitri; Lee, H. N.; Katiyar, R. S.; and Xi, X. X.. (2009). "Ferroelectric Phase Transitions in Three-Component Short-Period Superlattices Studied by Ultraviolet Raman Spectroscopy". Journal of Applied Physics, 105(5), 054106-1 - 054106-5. http://dx.doi.org/10.1063/1.3087611