Abstract: A New Niobate Ba₅LaTi₂Nb₃O₁₈ was synthesized by a high temperature solid state reaction in the BaO-La₂O₃-TiO₂-Nb₂O₅ system. The chemical compositions, crystal structure, microstructure, density and melting point of the new compound were characterized by EPMA, XRD, SEM, DTA and so on. Ba₅LaTi₂Nb 3O₁₈ crystallizes the rhombohedral system with unit cell parameters a=0 573 25(2) nm, c=4 213 9(2) nm, and space group R3m, Z=3. The structure may be described as five (Nb,Ti)O₆ octahedra corner-sharing along c axis to form perovskite layer connected by Ba atoms. The Ba₅LaTi₂Nb₃O₁₈ ceramic exhibits a high dielectric constant of 80.5, low dielectric loss of 6.5×10^-4 and small temperature coefficient of dielectric constant of -78×10^-6 K^-1 at 1 MHz due to its close structure and relative high dielectric polarizabilities of Ba²⁺, La³⁺, Ti⁴⁺ and Nb⁵⁺. Ba₅LaTi₂Nb_{3O18 might be a suitable candidate of high εr microwave dielectric ceramics.}

Key words: Niobate, Perovskite-related structure, Dielectric property