Variation of ferroelectric hysteresis loop with temperature in (SrxBa1−x)Nb2O6 unfilled tungsten bronze ceramics

The ferroelectric switching properties of (SrxBa1−x)Nb2O6 (x = 0.25, 0.5, 0.75) unfilled tungsten bronze ceramics have been investigated over a broad temperature range. At room temperature, the saturated polarization-electric field (P-E) loop is determined for x = 0.25, and it becomes slimmer with increasing x, which indicates the evolution from normal ferroelectric to relaxor ferroelectric. Studies on domain structure by piezoresponse force microscopy (PFM) well confirm this conclusion. Under the same electric field for evaluating P-E loops, both the maximum and remanent polarizations tend to decrease and vanish at low temperatures for all compositions. This phenomenon is quite like the re-entrant relaxor behavior reported in some perovskite-type ferroelectrics. However, with increasing the electric field, the saturated P-E loops can be obtained at low temperatures for all compositions. This suggests that the decline of switchable polarization at low temperatures in (SrxBa1−x)Nb2O6 ceramics is due to the increase of coercive field rather than the decrease of the long-rang interaction of structural dipoles on cooling.