Structure and dielectric properties of Ba5NdCu1.5Nb8.5O30−δ tungsten bronze ceramics

A new type of tungsten bronze ceramic Ba5NdCu1.5Nb8.5O30−δ has been prepared by a conventional solid-state reaction technique. Its structural, dielectric properties were investigated. Rietveld analysis shows that Ba5NdCu1.5Nb8.5O30−δ has a single-phase tetragonal (space group P4bm and lattice constants a = b = 12.4961(4) Å, c = 3.9426(8) Å, V = 615.66(4) Å3) tungsten bronze structure. The occupations of sites A and B are quite interesting. A1 sites are fully disordered occupied by Ba ions and Nd ions and A2 sites for Ba ions only, while B-sites are equal for both Cu and Nb ions to occupy. This material exhibits an obvious relaxation behavior in the 213–573 K temperature range. The dielectric constants have been fitted by the modified Curie–Weiss law and all the estimated γ values are close to 2, confirming the typical relaxor ferroelectric behavior. The disorders of Ba2+ or Nd3+ in A1 sites and Nb5+, Cu2+ in B sites induced by the oxygen vacancies may contribute to this dielectric behavior.