Citrate Route to Sn-Doped BaTi4O9 with Microwave Dielectric Properties

Highly reactive and nanometer-sized (30–50 nm) Sn-doped BaTi₄O₉ (BaTi_{4- x} Sn _x O₉; x = 0.0–0.03) powders have been prepared by the citrate-precursor method. The effect of Sn substitution on the crystallization and microwave dielectric properties has also been investigated on the basis of microstructure and crystal structure. Addition of a small amount of SnO₂ resulted in a lowering of the sintering temperature of BaTi₄O₉, and at 1250–1300°C for 2–5 h, dense compounds with a theoretical density up to 99% could be obtained. The Sn-doped BaTi₄O₉ materials were found to have excellent microwave dielectric properties with epsilon_r = 34–37, Q = 8300–8900 at 11 GHz and tau_f = 3.6–16.1 ppm/°C.