The effect of TiCl_3 on the microstructure of donor-doped boron-added Ti-excess BaTiO_3

摘要

The effect of T1Cl_3 and 0.5, 1.0, 2.0mol percent B_2O_3 addition on the microstructure and on the densification of Ti-excess BaTiO_3, were investigated. Sb_2O_3 was used as a donor dopant in boron containing compositions. The Ti-excess, platelet-type Ba_2Ti_5O_(12) or Ba_4Ti_(12)O_(27) phases were detected in undoped and Ti-excess formulations and compositions doped with 0.5 mol percent B_2O_3, which were sintered below the eutectic temperature. Suppression of these platelet-type grains occurred in the formulations containing more than 0.5mol percent B_2O_3. Donor doping by Sb_2O_3 was very effective for promoting twin formation due to the increased concentration of the Ti~(3+) ions. Sudden grain growth occurred at the 2 mol percent B_2O_3 addition level, with the loss of twin lamellae within the structure. The addition of 0.2 mol percent excess TiO_2 in liquid form (TiCl_3) to the 0.5 mol percent B_2O_3 containing sample, reduced the size and the number of polygonal grains and had a marked effect on the twin formation due to the homogeneous distribution of the excess Ti ions in the composition. The effects of adding the grain boundary modifier B_O_3 (before and after the calcination step) on the microstructure and on the positive temperature coefficient of resistivity (PTCR) of Sb_2O_3 donor-doped Ti-excess barium titanate (BT) were also investigated; PTCR effects up to 5.0 orders of magnitude were obtained.