Nanoscale Investigation of Degradation Effects in Lead Zirconate Titanate by Piezoresponse Force Microscopy
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Date
2005-08-22
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Abstract
This thesis reports results obtained by piezoresponse force microscopy (PFM) on the nanoscale mechanisms of imprint and fatigue, two of the most important degradation effects in ferroelectric materials. Imprint is the preference of a ferroelectric material for one polarization state over another. Fatigue is the loss of polarization due to repeated switching.
Imprint was investigated in three PZT films with thicknesses of 100, 300, and 500 nm. It was found that the imprint was most severe in the thinnest sample. This was attributed to the increasing dominance of interface effects in the thin sample. Furthermore, it was found that the presence of top electrodes moderated the imprint. This was explained by top electrode leading to a symmetric distribution of trapped space charge, as opposed to the asymmetric distribution when only the bottom electrode is present.
Fatigue was investigated in bulk ceramic PZT samples cycled to three different fatigue states (virgin, semifatigued, and fatigued) and then polished at an angle such that a range of thicknesses in the sample were available to be studied. It was found that the fatigued samples exhibited different domain structures. Backswitching occurred in the thick regions of the fatigued sample, but did not occur at any thickness in the virgin sample. This was explained by the cascaded backswitching model, positing that charged defects agglomerating at grain boundaries and provoking backswitching in all grains above it.
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Keywords
piezoresponse force microscopy, degradation effects, ferroelectric, PZT
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Degree
MS
Discipline
Materials Science and Engineering
