Improved microwave dielectric properties of novel low-permittivity Sn-doped Ca_2HfSi_4O_(12) ceramics

摘要

The phase compositions and microwave dielectric properties of Ca-2(Hf1-xSnx)Si4O12 (0 = x = 0.5) were investigated by the solid-state reaction method. A single-phase ceramic with monoclinic structure was formed in the Ca-2(Hf1-xSnx)Si4O12 (0 = x = 0.2) ceramic. At 0.25 = x = 0.5, CaSiO3 and CaSnSiO5 second phases appeared. The microwave dielectric properties of a novel Ca2HfSi4O12 ceramic (epsilon(r) = 8.1, Q x f = 39,700 GHz and tau(f) = -12.7 ppm/degrees C) were obtained. Partial substitution of Sn4+ for Hf4+ could reduce its relative permittivity and improve quality factor, and the highest quality factor of 49,500 GHz was obtained at x = 0.2. The tau(f )value of Ca-2(Hf1-xSnx)Si4O12 ceramics could be controlled to a near-zero value by the CaSnSiO5 second phase when x 0.3. The optimum microwave dielectric properties (epsilon(r) = 8.0, Q x f = 37,100 GHz and tau(f) = -7.2 ppm/degrees C) were achieved in the Ca-2(Hf1-xSnx)Si4O12 (x = 0.4) ceramic.