Effect of temperature annealing on periodically poled rare-earth doped lithium niobate crystal

Rare earth doped Periodic Poled Lithium Niobate crystals prepared by the off-centered Czochralski growth technique have been submitted to several annealing proceses either at T>T_c as T<T_c. It is shown that an annealing process at T>T_c eliminates the periodic domain structure in the surface but not in the bulk crystal, where the periodic structure is not damaged for a low cooling rate, while it is strongly damaged for a quenching process. When the annealing process is performed at temperatures very close to the Curie temperature but below, the periodic domain structures do not disappear even from the surface, but they are strongly damaged when temperature is cooled down following a quenching procedure. When temperature is reduced following a low cooling rate process the surface domain structure is not affected.