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Edge-defined film-fed growth of single-crystal piezoelectrics

Author(s)
Nunes, Benjamin P. (Benjamin Paul), 1976-
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Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.
Advisor
Yet-Ming Chiang.
Terms of use
M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission. http://dspace.mit.edu/handle/1721.1/7582
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Abstract
Many transducer technologies would benefit tremendously from the development of shaped, oriented single-crystals, of a high-strain, piezoelectric material. Recently, unusually high electrostrictive and piezoelectric actuation has been observed in polycrystals and flux-grown <100> single-crystals of ... Using seeded, Edgedefined Film-fed Growth (EFG) and the related Stepanov Technique (ST), low-hysteresis, highstrain, <100> and <111> oriented, single-crystals of BNBZT can be grown in rod and fiber form, with direct applications in active fiber composites and related devices. For this work, <100> and <111> oriented, single-crystal rods and fibers were grown via ST and EFG. Fibers, 260-700[mu]m in diameter and over 1.0 meter long, were grown using a custom built EFG machine and a capillary-shaper; rods, 2-3mm in diameter, up to 110mm long were grown using a floating-shaper. In all cases, strontium titanate (STO) was found to be an effective seed crystal. <111> oriented tetragonal crystals generated low hysteresis actuation consistent with a polarization rotation mechanism [14], but with only modest strains: ... <100> oriented tetragonal BNBZT generated high strains up to ... with hysteresis consistent with 90° domain switching. Electromechanical actuation and crystal structure in this system appear to be strongly affected by deviations from stoichiometry (B-site vacancies). Barium segregation and bismuth vaporization can also compromise electromechanical performance. Hypotheses are posed to explain the low actuation seen from <111> oriented ferroelectrics, and the effects of cation deficiencies on phase-stability. Cracks, pores, and other growth challenges encountered in ST and EFG growth of BNBZT are described.
Description
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2001.
 
Includes bibliographical references (leaves 97-99).
 
Date issued
2001
URI
http://hdl.handle.net/1721.1/17530
Department
Massachusetts Institute of Technology. Department of Materials Science and Engineering
Publisher
Massachusetts Institute of Technology
Keywords
Materials Science and Engineering.

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