Creation of domains by direct electron beam writing in magnesium-doped LiNbO3 and LiNbO3:Fe single crystals

• The periodic domains are created in crystal LiNbO3:Mg by direct electron beam writing.
• Periodic domains appear only at equilibrium between switching and screening times.
• Equilibrium exists in crystal co-doped by Fe.
• Shape and appearance of domains depend on the conductivity type.

Domain structures in the Z-cut of highly doped LiNbO3:Mg and LiNbO3:Mg,Fe single crystals were created by direct electron beam writing (DEBW). It was found that the value and type of electron conductivity influence the shape and number of domains thus created. Controlled electron beam regular domains were created only in samples of the crystal LiNbO3:Mg,Fe [MgO] = 5.16 mol.%, [Fe] = 0.007 mol.%. In highly doped LiNbO3:Mg ([MgO] = 5.19 mol.%) crystal, the domains were formed chaotically and controlled creation of domains did not occur. The domain shapes were analyzed in the framework of the theory of screening of domain nuclei depolarizing electric fields and the influence of screening on the final shape of domains. It was found that screening of intrinsic electric fields is faster in the LiNbO3:Mg,Fe crystal. This crystal has a high electronic conductivity of hopping type with a high mobility of charge carriers. Thus, a small amount of Fe provides equilibrium between the ferroelectric switching velocity and screening of the depolarizing electric field velocity. The results are discussed considering differences in the electron conductivity mechanisms, which control the screening of depolarizing electric field velocity and spatial charge area formed under an electron beam.