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

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.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Materials Science and Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2001

Author dc:creator

• Nunes, Benjamin P. (Benjamin Paul), 1976-

Advisor dc:contributor.advisor

• Yet-Ming Chiang.

• Materials Science and Engineering.

Statement dc:rights

• 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.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/17530

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/17530