Structure of strontium barium niobate Sr x Ba1 − x Nb2O6 (SBN) in the composition range 0.32 ≤ x ≤ 0.82

The structure of strontium barium niobate crystals SrxBa1-xNb2O6 is comprehensively studied in the whole range of the tetragonal tungsten bronze phase (x=0.32-0.82) using both powder and single-crystal X-ray diffraction measurements. Unit-cell parameters, density, site-occupancy factors and interionic distances show an explicit composition dependence which can be consistently explained using simple model calculations. The temperature dependence of the unit-cell parameters exhibits a remarkable anisotropy in a broad temperature region below the phase transition temperature. This proves that the electrostrictive contribution to the thermal expansion plays an important role in strontium barium niobate.