Abstract
Structural, microstructural, electrical properties and their thermal stability for (1−x)BF–xBT system where x ranges from 0.20 to 0.35 have been investigated. Its phase diagram shows a morphortropic phase boundary (MPB) with the coexistence of rhombohedral and pseudo-cubic phases for the composition around 0.275≤x≤0.30. The optimized piezoelectric properties with d33 varied from 50 to 136pC/N and the planar electromechanical coupling factor kp varied from 0.165 to 0.312 over a broad high Curie temperature range from 380 to above 600°C were obtained. The results indicated that samples with pseudo-cubic phase began to depole far below Curie point, while samples with rhombohedral phase showed good resistance to thermal depoling. A high thermal stability with Td=460°C, combining a high d33 value of 116pC/N, was obtained in (1−x)BF–xBT ceramics prepared by the conventional ceramic processing technique. The internal bias field in rhombohedral phase would stabilize the remnant polarization and favor the thermal stability.
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