Zt. Song et al., Structural and abnormal electrical properties of excess PbO-doped lead lanthanum titanate thin films, J PHYS D, 33(7), 2000, pp. 764-772
Lead lanthanum titanate (PLT) thin films with excess PbO (from 0 to 20 mol%
) were prepared by a metal-organic decomposition process. The ferroelectric
properties and current-voltage (C-V) characteristics of PLT films were inv
estigated as a function of the excess PbO. Abnormal ferroelectric and C-V p
roperties were observed in PLT films with excess PbO. The polarization agai
nst applied electric field (P-E) hysteresis loops were pinched before satur
ation of polarization of the films, and C-V curves had four peaks instead o
f the two peaks found in the normal C-V curves. The abnormal level of the h
ysteresis loops and C-V curves deteriorate with increasing concentrations o
f excess PbO in the films. Electron probe microanalysis has revealed that t
here is excess Pb in PLT thin films. Anger electron spectroscopy has detect
ed that the Pb accumulates at the interfaces between the thin film and the
bottom electrode. Meanwhile, transmission electron microscopy has found tha
t PbO nanocrystals on the interface between the PLT thin film and the botto
m electrode, and clusters of vacancies and interstitials, in particular, ex
ist in the PLT grains. Therefore, a part of the excess PbO may accumulate a
t the domain wall of the grains and the grain boundaries and the interface
between the bottom electrode and film during the thermal annealing process
of the films. Meanwhile, the oxygen vacancies of the grains will increase w
ith the increasing concentration of the excess PbO in the films. The excess
PbO and oxygen vacancies act as pinning centres and have a strong pinning
effect on the domains. When the poling voltage is not large enough, part of
the domains can overcome the force of the pinning, and abnormal ferroelect
ric and C-V properties were observed.