Microwave Characteristics of BaO‐TiO2 Ceramics Prepared via a Citrate Route

Microwave dielectrics of the TiO 2 ‐rich BaO‐TiO 2 system (BaTi 4 O 9 and Ba 2 Ti 9 O 20 ) were prepared by the citrate route. Pure and well‐crystallized BaTi 4 O 9 and Ba 2 Ti 9 O 20 particles of nanometer size (30–50 nm) could be obtained by thermal decomposition of citrate gel precursors. After sintering at 1200°–1350°C (for 2–10 h), dense compounds with >90% of theoretical density could be obtained. Dielectric properties of disk‐shaped sintered specimens, in the microwave frequency region, were measured in the TE 01δ mode. They were found to have excellent microwave characteristics: for BaTi 4 O 9 , ε r = 36, Q = 4900 at 10.3 GHz, and τ f = 16 ppm/°C; and for Ba 2 Ti 9 O 20 , ε r = 37, Q = 5300 at 10.7 GHz, and τ f =−6.0 ppm/°C.