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Title: High field dielectric properties of hard PZT ceramics
Author: Stevenson, Paul John
ISNI:       0000 0004 2724 6836
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 1998
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At the present time there is an increasing demand for higher acoustic and electric power densities in piezoelectric transducers. The preferred material for such acoustic sources is hard (acceptor doped) lead zirconate titanate (PZT) ceramic due to a combination of desirable properties including high piezoelectric coupling factors, high ~, low electrical losses and good temperature stability. Four commercially available materials from two independent suppliers have been characterised; PZ26 and PZ28, obtained from Ferroperm Ltd, and PC4 and PC8 obtained from Morgan Matroc. The use of Mn as the acceptor dopant was found for the F erroperm materials, and Fe for the Morgan Matroc materials. A finer grain size was also observed in the Morgan Matroc materials by comparison with those from Ferroperm. Various dielectric properties of each material were investigated as a function of field amplitude, ageing time after poling and with regard to the effect of grain size and temperature. A 'threshold field' type of behaviour was observed for all materials followed by a linear increase in permittivity with field level. Such behaviour is related to the Rayleigh law, first introduced to model the behaviour of ferromagnetic materials. The most encouraging results were observed for the Morgan Matroc material with the PC8 exhibiting the most stable performance under high drive conditions. Linear plots of the real versus imaginary parts of the dielectric permittivity were observed for all materials as a function of field amplitude or ageing time an related to a ferroelectric domain wall translation mechanism. The corresponding values of tan Odw, the loss associated with domain wall translation were compared. Evidence was also found for intrinsic and reversible domain wall vibration contributions to the permittivity in the 'low field' region, while partial domain switching was observed on approaching the coercive field Ee. Field-driven de-ageing studies of poled and unpoled PZ26 ceramICS revealed a gradual reduction in the effective internal bias field Ei with time. For poled materials the reduction followed a logarithmic time law, whereas for unpoled materials an exponential decrease was observed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available