Soft phonon modes in Ba0.5Sr0.5TiO3 thin films studied by Raman spectroscopy

We have studied vibrational properties of Ba0.5Sr0.5TiO3 thin films grown by pulsed laser deposition on SrTiO3 and LaAlO3 substrates with SrRuO3 buffer layers by Raman spectroscopy over the temperature range from 5 to 300 K. The soft phonon modes were observed. The temperature dependence of the soft phonon frequency and the splitting of the triply degenerated soft mode into two components of A and E symmetries indicate the ferroelectric phase transition. The E soft mode is overdamped over a broad range of temperatures, and the A soft mode intensity decreases gradually in this range. This indicates a broad ferroelectric phase transition in the thin films. A comparison of results obtained from films deposited on SrTiO3 and LaAlO3 substrates shows that strain shifts the ferroelectric phase transition temperatures. (C) 2001 American Institute of Physics.