Effects of CaTiO3 and SrTiO3 Additions on the Microstructure and Microwave Dielectric Properties of Ultra-Low-Fire TeO2 Ceramics

In this study, microwave dielectric ceramics of TeO2 with various amounts of CaTiO3 and SrTiO3 were prepared. The densification, microstructural evolution, and dielectric properties of the ultra-low-fire ceramic composites were characterized. Three phases including TeO2, TiTe3O8, and CaTe2O5 or SrTe2O5 were observed in the CaTiO3- or SrTiO3-added TeO2 system. Eutectic reactions of the CaTe2O5-TeO2 and SrTe2O5-TeO2 systems occurred at 650 degrees and 590 degrees C, respectively, enhancing the densification through liquid-phase sintering. The X-ray diffraction observations were confirmed as the Raman spectra located at 450-520 and 780-820 cm-1 corresponded, respectively, to TiTe3O8 and CaTe2O5 or SrTe2O5. The densification temperatures of TeO2-CaTiO3 ceramics ranged from 630 degrees to 670 degrees C depending on the CaTiO3 content, while all TeO2-SrTiO3 ceramics were densified at 610 degrees C. TeO2-10 wt% CaTiO3 and TeO2-15 wt% SrTiO3 ceramics were found to sustain best performance in CaTe2O5-TeO2 and SrTe2O5-TeO2 systems. They showed the following major microwave dielectric properties: epsilon(r)approximate to 28.6, Qxf approximate to 15 600 GHz, and tau(f)approximate to-3.24 ppm/degrees C, and epsilon(r)approximate to 28.7, Qxf approximate to 12 400 GHz, and tau(f)approximate to-3.81 ppm/degrees C, respectively.