Ba_6-3xSm_8+2xTi₁₈O₅₄ High Dielectric Constant Microwave Dielectric Ceramics And Their Modification

solid solutions are the typical high-e microwave dielectric ceramics, which have very important applications in microwave communication technology as the key materials for microwave resonators and filters. In this thesis, effects of composition and sintering conditions upon the microstructures and microwave dielectric characteristics of Ba6-3xSm8+2xTi18O54 solid solution were investigated. Modification of microstructures and microwave dielectric properties were conducted by Nd substitution for Sm into the A-site, Sn substitution for Ti into the B-site and Nd/Sn cosubstitution for Sm/Ti into the A- and B-sites in the Ba6-3xSm8+2xTi18O54 solid solution. In addition, properly prolonging sintering was effective to improve microwave dielectric properties.Phase constitution, microstructures and dielectric properties of Ba6.3XSmg+2xTiigO54 ceramics were investigated as functions of composition and sintering condition. The solid solution limits were confirmed to be 09,OOOGHz) was obtained. It should be emphasized that the temperature coefficient of resonant frequency was significantly affected by sintering time and the zero-temperature coefficient composition shifted to Nd-rich side with increasing sintering time. The excellent microwave dielectric properties were achieved in the ceramics: s=85, Qf=9,460GHz, and Tf=+0.8ppm/C.In the B-site substituted ceramics, the Ba6-3XSm8+2x(Ti1-zSnz)18O54-based tungsten-bronze phase became unstable for compositions with Sn content equal to or greater than 10 mol%, where BaSni2O4 and Sm2(Sn,Ti)2O7 appeared, and, finally, these phases became the major phases. This is correlated with the decrease of tolerance factor and electronegativity difference. A small amount of Sn substitution for Ti improved the temperature coefficient of resonant frequency (tf) but the dielectric constant (e) and the quality factor (Qf) decreased because of the appearance of the secondary phases.Nd/Sn cosubstitution for Sm/Ti into the A- and B-sites in thesolid solution led to a good combination of high e, high Qf, and near-zero Tf. With increasing Nd content, both e and Qf increased, but Tf value also became larger. Properly prolonged sintering could further increase Qf value, while reduced if in the present solid solutions. High Qf value (10,600GHz) was obtained in the present ceramics combined with high-e (80) and near-zero temperature coefficient(+11ppm/C).Generally, high-e microwave dielectric ceramics used as resonators and filters can be achieved in Ba6-3XSm8+2xTii8O54 solid solutions. High Qf value (>10,000GHz) was obtained combined with high-e and near-zero temperature coefficient. Effect of ion substitution and sintering conditions upon microstructures, subsequently upon dielectric properties were clarified.