Substitution site of La ions in La-doped Bi4Ti3O12-SrBi4Ti4O15 intergrowth ferroelectrics

Several lanthanum-doped intergrowth ferroelectric materials of type Bi4−xLaxTi3O12-SrBi4−yLayTi4O15 [BLT-SBLT(x+y)] were prepared with the lanthanum content, (x+y), ranging from 0.00 to 1.50. XRD patterns imply that the lattice space of (1 1 6) for Bi4Ti3O12-SrBi4Ti4O15 is the average of those of (1 1 5) for Bi4Ti3O12 and (1 1 7) for SrBi4Ti4O15. By assuming that this relationship is not affected by doping, the La ion substitution site is calculated. The results indicate that La ions show pronounced site selectivity for the BTO blocks when the La content is lower than 1.25. As (x+y)=1.50, more La ions substitute the Bi ions in SBTi blocks. These calculated results are consistent with the estimation from their Curie temperature.