Fabrication of Bi_3NbTiO_9 Thick Films by Air Flow Deposition

摘要

Ferroelectric thick films of Bi_3NbTiO_9 (BNT) with Aurivillius type structure were fabricated using the airflow deposition method at room temperature. The precursor powder for deposition was prepared by a conventional mixed oxide route. The BNT films obtained from airflow deposition had thickness between 25 and 90 μm. Subsequent sintering showed that the films were sinterable at lower temperatures than bulk samples prepared from the same powder using isostatic cold pressing technique. Thick films sintered at 900 ℃ displayed higher density and a higher electrical breakdown field compared with bulk samples. SEM microscopy showed similar grain size for the thick films sintered at 900 ℃ and corresponding bulk samples sintered at 1150 ℃. A pronounced preferential grain orientation of 70% along the c-axis was observed for thick films with thickness of 25μm sintered at 900℃. While the grain orientation in bulk samples was random the grains in the thick films were aligned along the substrate plane. This significant microstructural difference between thick film and bulk samples is believed to be associated with directional nature of the deposition process. The novel method allowed anisotropic film formation without applying pressure during sintering. Low sintering temperature allows reduction in bismuth losses and better grain growth control, which also contributes to the advantages of the method.