Phase transition, high figure of merit and polar nano-regions in dielectric tunable lanthanum substituted barium titanate

Ba_1-xLa_xTi_{1 -x/4}O₃ (BLT, x = 0-0.08, abbreviated as BLT100x) ceramics were prepared by using a solid state reaction process. Their phase transition, surface morphology, dielectric properties, tunability and ferroelectric behaviors were examined. Substitution of La at A-site in BaTiO₃ leads to a downward shift of Curie temperature and diffused cubic-tetragonal (C-T) phase transition. BLT6 exhibits a high tunability (35.4 at 20 kV/cm), a low dielectric loss (0.002) and a high figure of merit (177 at 20 kV/cm) at 10 kHz and room temperature. The nonlinear dielectric behavior under the applied electric field is well described by the multipolarization model. And the temperature dependence of ferroelectric hysteresis loops proves that the field induced phase transition is restrained by substitution of La in BaTiO₃, whereas polar nano-regions (PNRs) which are an extrinsic polarization contribution are present in BLT and play an important role to the high dielectric tunability of BLT.