Properties and lanthanum distribution of Bi4−xLaxTi3O12−SrBi4−yLayTi4O15 intergrowth ferroelectrics

Using the standard solid-state reaction method, several lanthanum-doped intergrowth ferroelectric ceramics of type Bi4−xLaxTi3O12−SrBi4−yLayTi4O15 [BLT–SBLT (x+y)] were synthesized with the lanthanum doping content, (x+y), ranging from 0.00 to 1.50. The remnant polarization (2Pr) of the samples, which varies with (x+y), has a maximum when x+y=0.50, that is nearly 60% greater than at zero doping. The Curie temperature Tc decreases monotonously with (x+y). By assumpting that the Curie temperature of BLT-SBLT (x+y) is the average of Tcs for its two constituents BLT and SBLT, La distribution in each constituent is estimated. The result demonstrates that when (x+y) is small (⩽1.25), La concentration in BLT constituent is higher than that in SBLT; but when x+y=1.50, more La3+ ions would prefer substituting the Bi3+ ions in SBTi. This finding agrees well with the behavior of d(118) lattice space as well as the relaxation characteristics observed in BLT–SBLT(1.50).