Lattice dynamics in BaxSr1-xTiO3 single crystals:: A Raman study -: art. no. 174302

The lattice dynamical properties of BaxSr1-xTiO3 single crystals with x=0.05, 0.1, 0.2, 0.35, and 0.5 have been studied by Raman spectroscopy in the temperature range 5-300 K. We present the data on the composition and temperature dependence of the phonon modes in BaxSr1-xTiO3, in particular, the soft modes. At low temperatures, the well-defined E and A(1) soft modes have been observed in the crystals of all compositions studied. For low Ba content (x<0.2) the soft modes extrapolate to zero and remain underdamped in the entire temperature range, indicating the displacive type of the ferroelectric phase transition. For xgreater than or similar to0.2, i.e., in the composition range of the BaxSr1-xTiO3 phase diagram where three ferroelectric phases exist, the soft modes exhibit less softening and become heavily damped in the temperature range corresponding to the orthorhombic and tetragonal phases. This demonstrates that the order-disorder-type behavior becomes stronger with increasing Ba content. However, no first-order Raman scattering in the cubic phase was observed in BaxSr1-xTiO3 of compositions studied, in contrast to pure BaTiO3. The temperature behavior of the A(1) soft mode indicates that the ferroelectric phase transition is of the first order in BaxSr1-xTiO3 with xgreater than or similar to0.2, and turns into the second order for smaller Ba concentrations.