DIELECTRIC-PROPERTIES OF (BA, SR)O-(SM, LA)2O3- TIO2 CERAMICS AT MICROWAVE-FREQUENCIES

The dielectric properties of (Ba, Sr)O-(Sm, La)2O3-TiO2 material at microwave frequencies were investigated. By varying the amount of strontium from 0-25 mol % in the 0.15(Ba1-xSrx)O-0.15Sm2O3-0.7TiO2 composition, it was possible to adjust the frequency temperature coefficient, tau(f), from - 13 p.p.m. degrees-C-1 to + 30 p.p.m. degrees-C-1. When 7 mol % Sr was substituted for barium, tau(f) = 0 p.p.m. Degrees-C-1 was obtained. TiO2 with rutile phase (Tau(f) almost-equal-to 400 p.p.m. degrees-C-1) acted as a dominant element in tau(f) variation of the 0.15(Ba1-xSrx)O-0.15(Sm1-yLay)2O3-0.7TiO2 (0 less-than-or-equal-to x less-than-or-equal-to 0.25, 0 less-than-or-equal-to y less-than-or-equal-to 0.6) system. Additionally, increasing the quantity of lanthanum substitution for samarium had a greater positive effect on tau(f) than strontium substitution for barium. When 60 mol % La was substituted for samarium with 7 mol % Sr substitution barium, tau(f) of the system reached 95 p.p.m. degrees-C-1. The effect on microwave dielectric characteristics of the 0.1 5(Ba0.93Sr0.07)O-0.15SM2O3-0.7TiO2 (BSST) ceramics by varying the calcination and/or sintering conditions or doping additives, were studied. The added SnO2 acted as a firing agent to lower the sintering temperature, and the dielectric Q(Q(d)) value was improved by properly adding CdO. With 1 wt% CdO addition, the highest Q(d) value of the BSST resonator, after calcination at 1100-degrees-C/2 h and sintering at 1370-degrees-C/4 h, reached 4180 at 4 GHz with a small tau(f) of - 4 p.p.m. degrees-C-1 and an epsilon(r) of 80.7 was obtained.