Abstract: Two new niobates Ba₅YZnNb₉O₃₀ and Ba₅LaZnNb 9O₃₀ were synthesized by high temperature solid-state reaction in the BaO-Ln₂O₃-ZnO-Nb₂O₅ system. The crystal structure and dielectric properties were characterized by using X-ray powder diffraction, scanning electron microscope and dielectric measurements. The results show that Ba₅YZnNb₉O₃₀ belongs to ferroelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters: a=1.252 55(4) nm, c=0.395 30(2) nm. Ba₅YZnNb₉O₃₀ has significant relaxor behavior, and the phase transition from ferroelectric to paraelectric occurred at 25 ℃ as frequency was at 10 kHz. The room temperature dielectric constant(ε_r) of Ba₅YZnNb₉O₃₀ ceramic reached 456 at 1 MHz. While Ba₅LaZnNb₉O₃₀ belongs to paraelectric phase of fully filled tetragonal tungsten bronze structure at room temperature with unit cell parameters: a=1.257 31(3) nm, c=0.398 12(2) nm. The room temperature dielectric constant(ε_r) of Ba₅LaZnNb 9O₃₀ ceramic reached 316 combined with a low dielectric loss of 0.017 at 1 MHz.

Key words: Niobate, Tungsten bronze structure, Dielectric property