Evolution of structure, dielectric properties, and re-entrant relaxor behavior in Ba5LaxSm1−xTi3Nb7O30 (x = 0.1, 0.25, 0.5) tungsten bronze ceramics

The effects of A site occupation on the structure, dielectric, and re-entrant relaxor behaviors were studied for Ba5LaxSm1−xTi3Nb7O30 (x = 0.1, 0.25, 0.5) tungsten bronze ceramics. The tetragonal tungsten bronze structure in space group P4bm was indicated for all compositions. The dielectric and ferroelectric properties were investigated over a broad temperature range. For all compositions, broad permittivity peaks with strong frequency dispersion were observed, where the peak points well fitted the Vogel-Fulcher relationship. The temperature dependency of ferroelectric hysteresis loops indicated the re-entrant relaxor behavior for all compositions: both the maximum and remanent polarization tended to decrease and vanish at low temperatures. In Ba5LaxSm1−xTi3Nb7O30, the re-entrant temperature (Tr) decreased with La-substitution, and the reduced remanent polarization at Tr (PTr) was determined. It seemed that the A1 site cation substitution exerted direct effects on the long-range ferroelectric order, and then the re-entrant relaxor behavior.