Property-structure relationship in lead-free relaxors Ba5RSn3Nb7O30 with tungsten bronze structure

Abstract

Lead-free relaxors Ba5RSn3Nb7O30 (R = La, Nd, Sm) with a tetragonal tungsten bronze structure were prepared by a standard solid-state reaction process, and the dielectric and ferroelectric properties were systematically determined together with the structures and microstructures. Rietveld refinement results suggested that a single-phase tungsten bronze structure in space group P4/mbm was obtained for all the compositions. Both the dielectric constant (ε′) and the dielectric loss (tan δ) exhibited a broad maximum with evident frequency dispersion far below room temperature, which indicated the typical relaxor nature. The selected area electron diffraction patterns revealed that the relaxor behavior in the present system originated from the incommensurate structure modulation. The dark-field transmission electron microscopy images confirmed the presence of polar nanoregions in the areas generating the satellite reflections of incommensurate structure modulation, which implied a possible correlation between the incommensurate structure modulation and polar nanoregions in tungsten bronze relaxors.