| Lead-based ferroelectric perovskites such as PbTiO{dollar}sb3{dollar} (PT), Pb(Zr,Ti)O{dollar}sb3{dollar} (PZT), and (Pb{dollar}sb{lcub}rm 1-x{rcub}{dollar},La{dollar}sb{lcub}rm x{rcub}{dollar})(Zr{dollar}sb{lcub}rm y{rcub}{dollar},Ti{dollar}sb{lcub}rm 1-y{rcub})sb{lcub}rm 1-x/4{rcub}{dollar}O{dollar}sb3{dollar} (PLZT) have applications in electrical and optical areas such as holographic memories, electro-optical light modulators, and optical bistable valves or shutters owing to their unusual characteristics in photoinduced change of refractive index, electro-optic effect, and bistable polarization.; The Deposition by Aqueous Acetate Solution (DAAS) technique has been developed for the preparation of PT, PZT, and PLZT ferroelectric powders and thin films. The advantages of DAAS technique include: (1) the formulated precursor solutions are stable with no discernible gelation or precipitation for several months, (2) the precursor solutions can be formulated to within better than 1% of the desired stoichiometry, (3) because this is an aqueous process, it is a non-moisture-sensitive alternative to sol-gel techniques, (4) water soluble acetate, acetylacetonate, or carbonate salts of various metal ions could be easily added to the solution to prepare extrinsically doped materials, and (5) the process uses water as solvent, which is "environmentally friendly".; Stoichiometric, non-stoichiometric, and thermal diffusion ion-doped PZT and PLZT perovskites were prepared by DAAS technique at relatively low annealing temperature of 550-650{dollar}spcirc{dollar}C. A precise stoichiometric PZT precursor solution formulated by the DAAS technique has produced a perovskite film of excellent P-E hysteresis loop and fatigue behavior. The characterization results show that the stoichiometric precursor-processed doped ions are strongly bonded in the perovskite lattice, whereas the thermally diffused ions are more weakly bound in the grain boundaries.; Excitation photocurrent spectroscopy (EPS) was used to record photoconductivity from 200 to 600 nm for a PZT thin film. The EPS spectrum of the thermally diffused Fe-doped PZT thin films shows four photocurrent peaks at 262, 338, 428 and 472 nm. The possible atomic and electronic assignments of EPS transitions are (1) Pb{dollar}sp{lcub}3+{rcub}{dollar} hole centers for the 262 nm band, (2) oxygen vacancy centers for the 338 nm band, and (3) Fe{dollar}sp{lcub}3+{rcub}{dollar} traps for the 428 and 472 nm bands.; Upon optical illumination with a N{dollar}sb2{dollar} laser at 337 nm, the photoelectrons lead to the generation of dark current which seems to relax quickly and create no space charge or photovoltaic effects. The photoelectrons screen the long-range field which favors the ferroelectric states, and avoid switching of the ferroelectric domains. When the PZT thin film was irradiated with a KrF laser at 248 nm, the creation of Pb{dollar}sp{lcub}3+{rcub}{dollar} hole carriers trap slowly, resulting in long-term conductivity. The external field polarity, such as applied +3 v and {dollar}-{dollar}3 v may be viewed as hole injection and electron injection respectively. The stimulation of hole/electron injections on the spontaneous polarization switching of 5 wt% Cr-, Mn-, Eu-, and Pr-doped PZT thin films has been illustrated for the possible application in the optical memory. |
