Refinement of the single-crystal structure of Sr0.61Ba0.39Nb2O6 : Ce

The results of a structure refinement of the Sr1-xBaxNb2O6 (SBN) single cry stals (x = 0.39) doped with small amounts (0.05%) of Ce are reported. An at tempt is made to elucidate the effect of the dopant Ce3+ on the distributio n of the Sr2+ and Ba2+ cations over channels of two types in the three-dime nsional framework. A model of incorporation of dopant Ce3+ into the SBN cry stal matrix is proposed on the basis of crystal-chemical considerations and specific features of the statistical distribution of the Sr2+ and Ba2+ cat ions. This model agrees well with the spectroscopic data. The X-ray diffrac tion data are collected on an Enraf-Nonius CAD-4F automated diffractometer (MoKalpha radiation, graphite monochromator, lambda = 0.7106, spherical cry stal with diameter (Zr = 0.17 mm). The parameters of the tetragonal unit ce ll are a = 12.458(2) and c = 3.936(1) Angstrom, space group P4bm, Z = 5, an d mu R = 1.2. The parameters of the crystal structure are refined with a se t of 2091 unique structural amplitudes. The final discrepancy factor with a llowance for the anisotropic thermal atomic vibrations is R-F = 2.9%.