Intergranular amorphous films and dislocations-promoted grain growth in SrTiO3

To investigate the effect of dislocations on grain growth in polycrystals, two sets of experiments were performed using SrTiO3 single crystals and SrTiO3 powder compacts. In the first set, with single crystals embedded in 2.0-mol%-TiO2-exess powder compacts, the growth of the single crystal was not affected by dislocations at 1300 deg. C, below the eutectic temperature, while it was enhanced by dislocations at 1470 deg. C, above the eutectic temperature, where the grain boundaries are wetted by an amorphous phase. In the second set, with 0.5-mol%-Nb2O5-doped powder compacts, the single crystal grew considerably into the SrTiO3 matrix grains in the presence of an amorphous film between the grains at 1470 deg. C both in 95N2-5H2 and in air, similar to the case of the TiO2-exess samples. However, when annealed at 1470 deg. C in 95N2-5H2 after pre-annealing at 1250 deg. C in 95N2-5H2, the amorphous phase remained at triple junctions and did not penetrate the grain boundaries, implying that this boundary configuration also is thermodynamically stable above the eutectic temperature. In this case, growth of the embedded single crystal was insignificant in spite of the presence of dislocations. These experimental observations indicate that the growth of SrTiO3 is promoted by dislocations only when an intergranular amorphous film is present at grain boundaries. The apparent ineffectiveness of dislocations on grain growth promotion without an intergranular amorphous film is discussed in terms of a low fraction of facetted grain boundaries and grain boundary drag by triple junctions