PHOTOINDUCED HYSTERESIS CHANGES AND OPTICAL STORAGE IN (PB,LA)(ZR,TI)O3 THIN-FILMS AND CERAMICS

Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 thin films and bulk ceramics are show n to exhibit two distinct, but related types of photoinduced changes i n their hysteresis behavior: (1) a photoinduced suppression of the swi tchable polarization and (2) a photoinduced voltage shift. Both effect s give rise to stable and reproducible hysteresis changes and, thus, e ither could be the basis of an optical memory. Both phenomena can be e xplained by trapping of photogenerated charge at domain boundaries to minimize internal depolarizing fields. The space-charge field that cau ses the voltage-shift effect is primarily due to the migration and sub sequent trapping of electrons. However, the thickness dependence of th e voltage shift implies that the trapped charge is not confined to the interface. The voltage-shift kinetics exhibit a stretched-exponential dependence, whereas the polarization-suppression effect follows an ex ponential time dependence. However, both effects exhibit similar relax ation times. In addition, the relaxation time for the voltage-shift ef fect decreases with increasing light intensity according to a power-la w relationship, tauis-proportional-toI-n, where 0.67 < n < 0.75.