| Summary: | 碩士 === 國立台灣工業技術學院 === 機械工程技術研究所 === 85 === ABSTRACT In this thesis, the ferroelectric to
antiferroelectric phase transformation of Pb0.99Nb0.02[(Zr1-
xSnx)1-yTiy]0.98O3 (PNZST) as a function of temperature and
field as well as the annealing effect on material properties
were investigated by measuring P-E curves, dielectric constants,
field-induced strains and remanent polarizations as function of
frequency.The PNZST powders were prepared by solution coating
method.Samples were sintered at 1200 ℃for 2 hours and heat
treatedat 1250℃for 2~60 hours using double-crucible method.
Polarization curves were measured with various frequenciesby
modified Sawyer-Tower circuit, and dielectric constants were
studied using a gain-phase analyzer. Field-induced strains as a
function of temperature were measured by means of a triangular
laser measuring system with an oil bath. Scanning electron
microscopy (SEM) and transmission electron microscopy (TEM) were
employed in microstructural analysis. Experimental results
show that samples can get larger remanent polarization(Pr) by
appropriate heat treatments, but Pr decreased with increasing
frequency and decreasing Ti content. Dielectric constant
maximum that occurs before multiple cell shows significant
increase by suitable heat treatment and increasing Ti content.
Dielectric relaxation disappeared at ferroelectric to
antiferroelectric transformation. Field-induced strains are
temperature dependent and the strains that use the same field
strength of 30kV/cm for 43/7/2 specimens treated at 1250 ℃for
20 hours can produce a maximum value of 0.22﹪around the
ferroelectric to antiferroelectric transition temperature (TF/A)
(at 77℃). When the temperature increased over TF/A, the field-
induced strain still showed a pronounced value of 0.16﹪, and
can achieve higher by increasing the field. The P-E curves of
43/7/2 show complete ferroelectric behavior, but the specimens
contain incommensurate phase from the results of microstructural
investigations, and the P-E curves can change to
antiferroelectric by increasing frequency, indicating that the
transition between the ferroelectric commensurate and the
antiferroelectric incommensurate phase is relatively easy, and
the incommensuration is the origin of the second-order
transition in this material. Ferroelectric to antiferroelectric
phase transition which shows similar behavior of the soft-mode
produces a maximum strain during transition. When the specimen
is over transformation temperature and in the antiferroelectric
imcommensurate phase range, high strain is produced by field-
induced AFE/FE transformation with a decoupling of the
polarization of the modulated polar structure.
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