X-ray-induced conductivity in iron-doped lithium niobate crystals

Illumination of photorefractive, iron-doped lithium niobate crystals $({\mathrm{LiNbO}}_3:\mathrm{Fe})$ with x-rays generates a conductivity that we determine from the speed of hologram erasure. The doping levels of the crystals and the acceleration voltage of our x-ray tube are varied. A theoretical model is presented, which describes the obtained results. A decrease of the conductivity with increasing ${\mathrm{Fe}}^{2+}$ concentration can be explained by assuming that holes are the dominant charge carriers for this short-wavelength illumination.