Study on Raman spectra of Bi4-xLaxTi3O12-SrBi4-γLaγTi4O15 intergrowth ferroelectrics

The Raman spectra of lanthanum-doped intergrowth ferroelectric ceramics Bi4-xLaxTi3O12-SrBi4-yLayTi4O15 [BLT-SBLT( x + y), x + y = 0.00, 0.25, 0.50, 0.75, 1.00, 1.25, 1.50] achieved at room temperature were investigated. The results show that La was substituted the Bi ions in the pseudo-perovskite blocks when U content is lower than 0.50. When U content is higher than 0.50, some of La ions are incorporated into the (Bi2O2)(2+) blocks. The incorporation of La ions into the (Bi2O2)(2+) layers would change the structure of (Bi2O2)(2+) and destroy its functions as the insulating layers and the space charge storage, which leads to the decrease of the remnant polarization. The relaxation characteristics observed in BLT-SBLT(1.50) are consistent with the softening of the mode lower than 30 cm(-1). This indicates that U-doping may bring about the structural phase transition.