Influence of Re-ions with different ionic radius in Ba12ReNb9O36 on crystal structure and microwave dielectric properties

Abstract The Ba12ReNb9O36 (Re Yb, Ce, Tm, Er, Y, Ho, Dy, Gd) ceramics are synthesized by solid-phase reaction method. The phase composition, crystal structure, microstructure, and microwave dielectric properties of the ceramics are investigated by X-ray diffraction, X-ray photoelectron spectroscopy, Scanning electron microscopy and Raman spectrum. The optimal microwave dielectric properties (er = 37.23, Q × f = 36600 GHz, and τf = 34 ppm/°C) are obtained for Ba12YbNb9O36 ceramic sintered at 1420 °C for 6 h. In this system, the variation of dielectric constant is dominated by polarizability. The Q × f is mainly affected by internal strain/fluctuation of d-spacing. The variation of τf is related to the temperature coefficient of dielectric constant and the oxygen octahedron distortion. Furthermore, the reduction of Ce4+ ions, the relative density, linear thermal expansion coefficient, and the second phase are also important factors affecting microwave dielectric properties.