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In the present work, the microstructure and microwave dielectric properties of BaTi4O9 ceramics derived from a sol-gel precursor were presented. Density measuring results demonstrated that the largest densities of ceramic sample about 96.7% could be reached by virtue of a cool iso-static press and a sintering process at at 1300 °C for 6 hours. The dielectric constant (εr), quality factor (Q×f) and the temperature coefficients (τf) of the BaTi4O9 ceramic samples were 36.65, 28000 GHz, +20.2 ppm/°C, respectively. XRD, SEM and XPS were used to characterize the microstructure of the ceramics samples. Substantial Ti3+ was proposed to be the cause of dielectric loss.

A modified polyacrylamide precursor method is presented to synthesize BaSm2Ti4O12 microwave dielectric ceramics. Under an alkaline circumstance, all the cations together with the monomer and bridging agent were dispersed into a hydrous solution with the aid of chelating agent EDTA. This mixture was initiated at about 90°C, dried, calcined at 1000°C for 2hs and finally turned into well-crystallized and single-phased BaSm2Ti4O12 ceramic powder, which was modeled and sintered at 1250°C for 2hours into well-sintered ceramics. Differential thermal analysis, thermogravimetric analysis, X-ray powder diffraction and transmission electron microscope were used to characterize the process. Microwave dielectric properties measured by a resonating cavity method contain a dielectric constant (εr) about 77.0 and quality factor (Q×f) lager than 11000.

BaTi4O9 - BaPr2Ti4O12 microwave dielectric ceramic composite powders were prepared by a polyacrylamide gel route using ethylenediaminetetraacetic acids (EDTA) as a chelating agent. This method provides a fast, cheap, reproducible and easy to scale-up way to prepare homogeneous mixed phases compounds. A light green, molecular-level, homogeneously mixed gel was prepared by the gelification of acrylamide. The precursors and derived oxide powders were characterized by thermal analysis (TG-DSC) and X-ray powder diffraction (XRD). Two phases and well-crystallized BaTi4O9 - BaPr2Ti4O12 composite powders were obtained at 1200 ºC for 4 h.