Synthesis and dielectric properties of Ba 1− xR 2 x/3 Nb 2O 6 (R: rare earth) with tetragonal tungsten bronze structure

Abstract

A series of new compounds, Ba 1−xR 2x/3Nb 2O 6 (RNd, Eu, Gd, Tb, Dy, Ho and Er) with tetragonal tungsten bronze (TTB) structure were synthesized. For Ba–R–Nb–O system, single phase TTB was obtained when X=0·25. To understand the formation condition of these TTB type compounds, two tolerance factors for TTB, t A1 and t A2, were proposed against the coordination polyhedra around A1 and A2 site cations, respectively. One of the factors was at least a requisition to stabilize crystal structure for all TTB type compounds. Ba 1− x R 2 x/3 Nb 2O 6 showed ferroelectric characteristics and the Curie temperature, T c , increased as the decrease of the ionic radius of rare earth cations. These new compounds have potential to be candidates to apply ferroelectric random access memory (FRAM).