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Development of bismuth ferrite derived piezoelectric ceramics for high temperature applications

Bennett, James Thomas (2014) Development of bismuth ferrite derived piezoelectric ceramics for high temperature applications. PhD thesis, University of Leeds.

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The foundations of this project lay in the authors research into the xBiFeO3-(1-x)(K0.5Bi0.5)TiO3 ceramic system. A broad pseudocubic region was identified where x = 0.4-0.3, these compositions produced large electric-field induced strains (>0.3%) due to the presence of polar nanoregions that are easily switched by an applied electric field, however, these return to a random order upon removal of the field. Positive-up negative-down (PUND) showed that ferroelectric switching was reduced in the pseudocubic region and synchrotron studies with an applied electric-field in-situ demonstrated predominantly reversible domain switching. Solid-solutions based upon the (1-x-y)BiFeO3-x(K0.5Bi0.5)TiO3-yPbTiO3 ternary system have been fabricated by conventional mixed oxide processing, this system is the primary focus of this thesis. Structural analysis using XRD established that long-range crystallographic order was present above a critical PbTiO3 concentration, in addition a broad mixed symmetry region was identified comprised of tetragonal and rhombohedral symmetries. The ferroelectric Curie temperature was between 410-590 ºC. Conventional ferroelectric and piezoelectric ordering was observed with the use of strain and polarization-field measurements. Rayleigh analysis was used to quantify the intrinsic and extrinsic contributions, a critical c/a ratio was identified at 1.045 with domain switching limited above this. Synchrotron x-rays with ex-situ electric-fields allowed for a more detailed structural analysis, selected compositions demonstrated significant phase changing behaviour. The room temperature tetragonal c/a ratio across the mixed symmetry region, Curie temperature, and piezoelectric d33 were found to correlate strongly with the PbTiO3 concentration in a number of compositions. This work demonstrates a number of important results that have wider implications. Ternary and pseudo-quaternary systems have recently been subject to large amounts of research as many of the possible binary systems have been exhausted. This has led to a raft of materials with reported high electric-field induced strains, these are often electrostrictive or have limited operating temperatures. The partial substitution of PbTiO3 promotes long-range non-centrosymmetric order, which leads to increased piezoelectric activity and TC.

Item Type: Thesis (PhD)
Keywords: Piezoelectric, Ferroelectric, Non-linear effects, Domain walls, Crystallography, High-temperature, PFM
Academic Units: The University of Leeds > Faculty of Engineering (Leeds)
The University of Leeds > Faculty of Engineering (Leeds) > School of Chemical and Process Engineering (Leeds)
The University of Leeds > Faculty of Engineering (Leeds) > School of Chemical and Process Engineering (Leeds) > Institute for Materials Research (Leeds)
Identification Number/EthosID: uk.bl.ethos.638870
Depositing User: Mr JT Bennett
Date Deposited: 25 Feb 2015 09:09
Last Modified: 25 Nov 2015 13:48
URI: http://etheses.whiterose.ac.uk/id/eprint/7473

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