Kinetic formation and thickening of intergranular amorphous films at grain boundaries in barium titanate

Kinetic formation and distribution of amorphous films at grain boundaries during grain growth have been studied in a model ceramic system, BaTiO 3, using single crystal/polycrystal bi-layers. Single crystal containing BaTiO 3 powder compacts with different TiO 2 additions (0.1, 0.4 and 1.0 mol%) were heat-treated at 1250 °C for 10 h in H 2 and then annealed at 1350 °C, above the eutectic temperature, in air for up to 50 h. During the air-annealing the single crystals grew into fine matrix grains of ∼2.0 μm diameter while no grain growth occurred in the matrix. With the growth of the single crystal, an amorphous film formed at the boundaries between the crystal and the matrix grains, and its thickness increased. As the amount of TiO 2 increased from 0.1 to 1.0 mol%, the film thickness increased about ten times. These experimental results show for the first time that: (i) grain growth in solid–liquid two phase materials can induce the formation and thickening of intergranular amorphous films at dry grain boundaries, and (ii) the film thickening is mainly due to the penetration of liquid pockets at triple junctions into the films formed during grain growth.