类钙钛矿新铌酸盐Ba6LaTi3Nb3O21的合成、结构与介电特性

A New Niobate Ba₆LaTi₃Nb₃O₂₁ was synthesized by 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, DTA and so on. Ba₆LaTi₃Nb₃O₂₁ crystallizes the rhombohedral system with unit cell parameters a=0.57388(2) nm, c=4.928 3(3) nm, and space group R3m, Z=3. The structure may be described as six (Nb,Ti)O₆ octahedra corner-sharing along c-axis to form perovskite layer connected by Ba atoms. The Ba₆LaTi₃Nb₃O₂₁ ceramics exhibits high dielectric of 74.1, low dielectric loss of 4.7×10^-4 and small temperature coefficient of dielectric constant of -69 ppm·K^-1 at 1 MHz due to its close structure and relative high dielectric polarizabilities of Ba²⁺, La³⁺, Ti⁴⁺ and Nb⁴⁺. Ba₆LaTi₃Nb₃O₂₁ might be a suitable candidate of high ε_r microwave dielectric ceramics.

Synthesis, Structure and Dielectric Properties of A New Pervoskite-related Niobate Ba6LaTi3Nb3O21