Marked increase in Curie temperature upon annealing of ferroelectric KF-substituted barium titanate

The effect of annealing on Curie temperature (TC) is investigated in ferroelectric KF-substituted BaTiO3 (KF-BT/x). We succeed in controlling TC of KF-BT/x from 262 to 384 K by annealing in oxygen. The thermal gravimetric analysis suggests that well-annealed KF-BT/0.10 does not contain F, indicating that the TC is enhanced by the evaporation of F. We propose that these marked changes in TC are achieved by strengthening the covalency between Ti and O (F) through the annealing.