Photorefractive properties of Cr-doped Sr0.61Ba0.39Nb2O6 related to crystal purity and doping concentration

The purity and the concentrations of the constituents Sr, Ba, Nh and Cr wer e determined in single crystals of chromium-doped Sr0.61Ba0.39Nb2O6 (SBN) b y instrumental neutron activation analysis (INAA) and X-ray fluorescence an alysis (XRF). Experiments with different Cr concentrations C-Cr reveal cons tant Sr and Ba concentrations as well as a decreasing Nb concentration with an increasing C-Cr. Therefore, Cr is incorporated at Nb lattice sites. The distribution coefficient of Cr is 1.2 between 100 and about 7000 ppm Cr an d 1 above. From measurements of the holographic two-beam coupling gain Gamm a for different C-cr, we deduced response times for the buildup of holograp hic gratings. The saturation value of Gamma depends in a nonlinear manner o n C-Cr and reaches its maximum at about 6000 ppm Cr. The inverse photorefra ctive response time of the grating erasure depends linearly on the erasure intensity for all doping concentrations. Thus a one-center model can be ass umed for the charge transport in SBN:Cr.