Defects, Structure Changes, and the Effect of Random Fields on the Displacement of Off-Center Ions in Sr_(0.5)Ba_(0.5)Nb_2O_6 Doped with Combinations of Ce and Cr

摘要

Synchrotron X-ray powder diffraction data are analyzed in detail by the Rietveld structure refinement program to obtain microscopic structure changes of Sr_(0.5)Ba_(0.5)Nb_2O_6 (SBN50) doped with combinations of Ce and Cr. The defects of Ce and (Ce,Cr)-doped SBN50 are determined by the densification behavior, and it is found that creation of Nb vacancies and self-compensation are the defect reactions for Ce and (Ce, Cr) dopants, respectively. The variations of the lattice parameters of a and c axes with doping content are determined by the changes of the distance between A1 and A2 sites via Coulomb interactions and the mean bond length of Nb(1)-O(4), respectively. It is confirmed that the polarization of SBN50 is mainly determined by the displacement of Nb ions. The effect of random fields induced by the impurities of the combinations of Ce and Cr on the displacement of off-center Nb ions has been reasonably explained.