X-ray powder diffraction methods for the determination of composition and structural parameters of Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals

• Undoped SBN, SBN:Cr, and SBN:Ni crystals were grown by the Stepanov technique.
• The crystal structures were refined by the Rietveld method.
• The general composition of the crystals can be described as Sr∼0.55Ba∼0.39Nb2O6−δ.
• The relationship between the unit cell parameters and Sr and Ba content was found.
• The correlation between the structural parameters and dopant content was revealed.

The possibility of using the Rietveld method for refinement of main structural parameters of both nominally pure (SBN-1) and Cr- (SBN-2: Cr2O3, 0.01 wt.%) and Ni- doped (SBN-3 and SBN-4: Ni2O3, 0.05 wt.% and 1.0 wt.%, respectively) ground relaxor-ferroelectric crystals of initial composition Sr0.61Ba0.39Nb2O6, grown by the modified Stepanov technique, has been shown. It was established that the general composition of the crystals can be described as Sr∼0.55Ba∼0.39Nb2O6−δ with possible vacancies in the oxygen sites; the composition of SBN-4 crystal differs from other samples by another distribution of Sr ions over the crystallographic sites of the structure. The correlation between the thermal parameters of oxygen atoms and the disorder on their sites as well as the Ni content in SBN-3 and SBN-4 crystals has been found. The relationship between the unit cell parameters of undoped and Cr- and Ni-doped Sr0.61Ba0.39Nb2O6 crystals and Sr and Ba content, and second-order nonlinear susceptibility values, χ(2), has been revealed.