Splitting of Triggered Phase Transition in Bi4-xLaxTi3O12 Mixed Crystals

Phase transitions in Bi 4- x La x Ti 3 O 12 (BLT- x ) mixed crystals with a low La concentration ( x <0.66) were investigated by measuring the dielectric constant and hysteresis loop, and carrying out differential thermal analysis (DTA) and domain wall observations. It was found in BLT- x that the triggered transition, i.e., the tetragonal–monoclinic transition observed in Bi 4 Ti 3 O 12 (BiT, BLT-0), splits into two transitions, i.e., the tetragonal–orthorhombic and orthorhombic–monoclinic transitions, with the addition of La ions. The temperature of the tetragonal–orthorhombic transition remains unchanged at about 673 °C, whereas that of the orthorhombic–monoclinic transition strongly depends upon the La concentration in the range of 0≤ x ≤0.66. The phase transitions and their symmetry changes were discussed on the basis of the Landau theory.