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A barium titanate precursor with a barium:titanium ratio of 1:4 was prepared by controlled coprecipitation of mixed barium and titanium species with an ammonium oxalate aqueous solution at pH 7. The results of thermal analysis and IR measurement show that the obtained precursor is a mixture of BaC 2 O 4 ⅐0.5H 2 O and TiO(OH) 2 ⅐1.5H 2 O in a molar ratio of 1:4. Crystallized BaTi 4 O 9 was obtained by the thermal decomposition of a precipitate precursor at 1300°C for 2 h in air. The dimensions of the powder calcined at 1000°C are between 100 and 300 nm. The grain dimensions of the sintered sample for 2 h at 1300°C are of the order of 10 to 30 m. Dielectric properties of disk-shaped sintered specimens in the microwave frequency region were measured using the TE 011 mode. Excellent microwave characteristics for BaTi 4 O 9 -‫؍‬ 38 ؎ 0.5, Q ‫؍‬ 3800 -4000 at 6 -7 GHz and f ‫؍‬ 11 ؎ 0.7 ppm/°C-were found.

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