  In this work, the effects of thermal annealing at 500 {\deg}C on
aerosol-deposited
$0.65\text{Pb}(\text{Mg}_{1/3}\text{Nb}_{2/3})\text{O}_{3}-0.35\text{PbTiO}_{3}$
thick films on stainless-steel substrates are investigated using two
complementary methods at high and low applied external electric fields. The
first one is Positive Up Negative Down method, which allows us to obtain
information about the switching and non-switching contributions to the
polarization. It shows that the as-deposited film is ferroelectric before
annealing, since it has a switching contribution to the polarization. After
annealing, both the switching and non-switching contributions to polarization
increased by a factor of 1.6 and 2.33, respectively, indicating stronger
ferroelectric behavior. The second method is based on impedance spectroscopy
coupled with Rayleigh analysis. The results show that post-deposition thermal
annealing increases the reversible domain wall contribution to the dielectric
permittivity by a factor 11 while keeping the threshold field similar. This
indicates, after annealing, domain wall density is larger while domain wall
mobility remains similar. These two complementary characterization methods show
that annealing increases the ferroelectric behavior of the thick film by
increasing the domain wall density and its influence is visible both on
polarization versus electric field loop and dielectric permittivity.
