Abstract:
The
subject of study was the growth and nucleation of sol-gel deposited lead
zirconate titanate
(PZT) films of composition Pb(Zr0_52,Ti0_4g)O3 (PZT52/48). This
particular composition is on a phase boundary between titanium-rich tetragonally
structured PZT and the zirconium-rich rhombohedral phase. The coexistence and relative
instability of these phases is thought to be one of the origins of high piezoelectric
coefficients exhibited
by films of this composition.
The aims of this
study were to investigate variables affecting the piezoelectric
coefficients in
sol-gel deposited PZT52/48 thin films. Control of preferred orientation if
PZT52/48 films on
platinum-coated substrates was accomplished by manipulating
processing conditions, specifically pyrolysis temperature.
Corona
poling was investigated as an alternative to contact poling. Attempts were
made to find a set of
poling parameters which yielded consistent results. Piezoelectric
coefficients are
highly dependant on poling conditions, with coefficient being lower in
insufficiently poled films or those damaged by field induced sample cracking. It was
observed that
(001)/(100)-oriented samples with small grains had significantly lower
piezoelectric coefficients and were harder to pole than coarser-grained (00l)/(l00)-
oriented
samples. Samples with a more irregular grain structure and a wide distribution of
grain size had the lowest piezoelectric coefficients, irrespective of preferred orientation.
The
impact of grain size on piezoelectric coefficients was confirmed using the FWHM of
the
(200) reaction. Films with more irregular grain structures had higher FWHM than
those with more uniform
grains and had lower d33,f and e31,f.
Values of e31,f and d33f were plotted against (001) intensity a determined from xray
diffraction. It was difficult to determine any correlation between piezoelectric
coefficients and
(001) intensity. I comparison, there was a definite inverse correlation
between
d33,f, e31,f and FWHM, indicating that defect concentration has much more of an
impact on piezoelectric coefficients in polycrystalline thin films than (001) intensity as a
result of defect-induced domain
pinning.
