Sun, D; (2008) Deposition-patterning of lead zirconate titanate (PZT) using electrohydrodynamic atomization. Doctoral thesis , UCL (University College London).

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Abstract

This research develops a novel processing technique, namely electrohydrodynamic atomization, for forming lead zirconate titantate (PZT) in various structures. The capability to process PZT materials is crucial due to the demand in applications of sensors, capacitors and actuators. Structures from continuous films to columnar structures and track-structures need to be fabricated with high effectiveness, low cost and high accuracy. This study focused on investigating a new deposition-patterning technique to fabricate such versatile material. Electrohydrodynamic atomization is a novel processing technique which makes use of electric field induced flow (electrohydrodynamics) to deposit and pattern pre-designed structures. This research is comprised of three parts. In the first part, the properties of 0.6 mol/L PZT sol was studied, which include density, electrical conductivity, viscosity and surface tension. Then the sol was placed in a furnace and heat-treated and the ideal sintering temperature was determined. After that, the electrohydrodynamic atomization process was successfully utilized for spraying 0.6 mol/L PZT sol in the cone-jet mode. Important spraying parameters such as applied voltage, flow rate and distance between the needle and substrate were examined. The mode selection map for this sol was constructed from 5x10"'2 m3 s"1 up to the critical flow rate point above which the cone-jet mode is not obtainable. The PZT particles were deposited on metallic substrates and heat-treated at 650 °C. Microstructure of the deposit was studied. Nano-structured PZT particles were observed under the microscope and the average size of these spherical particles was approximately 100nm. Secondly, the influence of concentration of sprayed sol on the as-deposited structures was investigated. Continuous PZT films were obtained using 0.06 mol/L sols while columnar PZT structures which are used to form 1-3 composites were produced using 0.6 mol/L sols. The reason for this feature was discussed considering the droplets of different sizes and their evaporation. The growth of PZT columns was studied by observing the cross-sectional structures at 10s, 20s, 40s, 60s, 180s and 330s. The affect of substrate temperature on the columnar structure was also analyzed by studying the density of the columns. A 1-3 composite was produced by infiltrating photoresists into columnar structures. The dielectric properties of such composite and the continuous film were investigated. Thirdly, PZT track-structures were produced by electrohydrodynamic printing. Cracks within the printed structures were eliminated by adding polyvinylpyrrolidone (PVP) to 0.6 mol/L PZT sol. Different volume ratios from 1:1 to 1:4 were used when mixing PZT and PVP solutions. The microstructure of the PZT tracks printed using different solutions were investigated using optical microscope. The content of residual PVP polymer was examined and it elucidated that PVP was completely removed after heat treatment at 650 °C.

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