Annealing behavior of lithium niobate irradiated with He-ions at 100 K

In order to investigate the formation and the annealing of defects, x- and z-cut lithium niobate (LiNbO3) crystals were irradiated with 200 keV He-ions at a temperature of 100 K. Subsequently, thermal treatment was performed at temperatures of 250 deg. C and 300 deg. C, respectively. The defect concentration was measured by means of Rutherford-backscattering spectroscopy (RBS) using 1.4 MeV He-ions immediately after the irradiation at 100 K, after warming to room temperature as well as after thermal treatment. After the irradiation the x-cut crystal is apparently more damaged compared to z-cut which is a consequence of the preferential arrangement of displaced Nb-atoms on vacant octahedral sites. Upon thermal treatment the samples show a completely different annealing behavior. At an ion fluence of 1x1016cm-2, the defect concentration decreases for x-cut material, but increases for z-cut samples with increasing annealing time. This is explained by the formation of aligned dislocation loops during the thermal treatment.