Crystal structure of the high temperature phase of strontium barium niobate

Pure and undoped strontium-barium niobate Sr_{0.40}Ba_{0.60}Nb₂O₆ (SBN40) single crystals grown by the Czochralski method were investigated by single crystal X-ray diffraction methods. The study below T_{C} (429 K for SBN40) confirmed the structure with P4bm space group. Above this temperature the structure transforms into the paraelectric, centrosymmetric one with P4/mbm space group. Analysis of the recorded diffraction patterns allowed to observe several signs of crystal structure modulation. On the registered diffraction images satellite reflections were found. A modulation vector q=(δ,±δ,), where δ=0.3075(6) (at room temperature) was found and it was similar to that occurring in the SBN61. In addition, above the phase transition temperature on the (hk) planes with l integer a weak diffuse scattering was observed.