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Title: Characterisation and investigation into the degradation of bulk PZT ceramics
Author: Poole, Marlene E.
ISNI:       0000 0001 3494 5342
Awarding Body: London South Bank University
Current Institution: London South Bank University
Date of Award: 2007
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The aim of this research has been to improve current understanding ofthe structural and mechanical processes that determine the dielectric, elastic and piezoelectric Propertie ofceramic lead zirconate titanate (PZT). S Experimental work has focussed on the highly sensitive 'soft' PZT composition (Pbo.97Lao.Q2Zro.53Tio.4703) which was found to contain approximately 2at.% Pb-site donor (La) substitution, corresponding with a phase just on the tetragonal side of the tetragonal-rhombohedral phase boundary. PZT ceramics find applications in a wide and diverse range of fields however thermal heating, low resistance to fracture under tensile stresses, high driving fields, poor processing and fabrication can compromise the longterm stability and reliability ofdevices and lead to catastrophic failure. Specifically designed instrumentation including a mechanical compression module and an electrical Curie point measurement system were employed to perform mechanical and thermal experimental investigations and the standard electrical resonance technique was used to electrically characterise test samples. The study of piezoelectric domain switching in ceramic PZT is essential for understanding the mechanisms that accelerate degradation in these materials, and has formed the main focus of this research effort. For the first time, an empirical investigation into the mechanical, electrical and thermal degradation of ceramic PZT as a function of the micro-Raman response is presented. It has been demonstrated that micro-Raman spectroscopy is a viable non-destructive analysis tool for investigating domain switching behaviour via sensitive polarisation measurements. The Raman data obtained has enabled evaluation of poled and depoled sample regions and continuous analysis ofthe nature and degree ofdepolarisation under various external loads. Zero-load ageing experiments have enabled a profile of the dielectric and piezoelectric coefficient time stability and natural ageing rate to be established. Results show that losses reduce dramatically ~ 3,000 hrs after poling and retain useful properties for up to three years. Combined electrical and Raman data confirms that the thresholds for the onset of reversible and irreversible domain switching occur at 20MPa and ~30MPa respectively. Raman mapping experiments have shown that a direct relationship between ferroelastic domain switching and Raman intensity exists and that a close correlation between Raman lines and electromechanical properties also exists. The temperature threshold for the onset of reversible depolarisation was found to occur between 60°C and 100°C in virgin samples, and was instant for samples fatigued in three point bending. 90° switched domains induced by micro-indentation parallel to the direction of poling were readily observed using a micro-Raman mapping technique within a 4 - 6pm radius of the major crack extension. A fatigue degradation profile for PZT-5H has been obtained via in-situ three point bending experiments under continuous micro-Raman analysis, and a correlation with stress-deflection data achieved.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available