Citrate route to Sn-doped BaTi₄O₉ with microwave dielectric properties

Highly reactive and nanometer-sized (30-50 nm) Sn-doped BaTi₄O₉ (BaTi_4-xSn_xO₉;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 ε_r = 34-37, Q = 8300-8900 at 11 GHz and γ_f = 3.6-16.1 ppm/°C.