X-ray diffraction study of phase transitions in Sr_0.75Ba_0.25Nb₂O₆ between 20 K and 400 K

Abstract

X-ray powder diffraction patterns of the ferroelectric mixed crystal Sr_0.75Ba_0.25Nb₂O₆ are recorded in Guinier geometry in a temperature range between 20 K and 400 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 modulation of the structure. The lattice parameter c exhibit strong anomalous temperature dependence at 200 KT350 K, indicating the diffuse ferroelectric phase transition (DPT). The proceeding of the DPT is also detectable by an increase of the diffuse scattering around the (002)-reflection. The temperature dependence of the unit cell volume indicates further PTs below room temperature in this relaxor material.