X-ray diffraction study of phase transitions in Sr0.39Ba0.61Nb2O6 between 20 and 500 K

X-ray powder diffraction patterns of the ferroelectric mixed crystal Sr_0.39,Ba_0.61Nb₂O₆ (SBN-39) are recorded in Guinier geometry in a temperature range between 20 K and 500 K by means of the film-lift technique. The lattice parameters were refined for a single tetragonal structure in the whole temperature range ignoring the incommensurate (IC) modulation of the structure as well as a temperature dependent small splitting of reflections, most clearly observed for the (001)-type. These values show anomalies in the region of diffuse ferroelectric phase transition as well as below room temperature indicating the three other phase transitions. The splitting may be caused by a two-phase state of a relaxor-like ferroelectric system due to coexistence of polarized regions (clusters) and untransformed remnants of the para-phase.