Elastic properties of bismuth layer-structure perovskite single crystals studied by brillouin scattering

Elastic properties of bismuth layered perovskite compounds, La_xBi_4-xTi₃O₁₂ (LBT-x) and SrBi₂Ta₂Og (SBT), were examined at room temperature by Brillouin scattering. Elastic stiffness coefficients, c₃₃ and c₄₄, defined in the pseudotetragonal symmetry, were obtained. The longitudinal sound velocities propagating along the c axis, were 3985 m/s and 3118 m/s for the pure bismuth titanate (BTO) and SBT, respectively. The sound velocity of SBT is very slow and is believed to be related with the weak interlayer bonding of this layer-structure compound. A simple linear chain model showed that the difference in the sound velocity between BTO and SBT is mainly due to the difference in the c axis lattice constant. The sound velocity of LBT-x increased slightly with the increase of x, while c₃₃ seems to be insensitive to x.