Temperature dependence of ?f and its origin in MgTiO3-CaTiO3 microwave dielectric composites

As a key parameter of microwave dielectric ceramics, tau f is required to be near-zero and usually treated as a temperature-independent constant. However, the strong temperature dependence of tau f was observed in (1-x) MgTiO3-xCaTiO3 composites and the constituting phases. Especially for the composite with x = 0.06 and a nearzero average tau f (tau f,W) of - 2.3 ppm/degrees C, the normalized resonant frequency (f0 & x303;) first increased and then decreased with temperature, and tau f decreased significantly from 8.6 ppm/degrees C at - 40 degrees C to - 13.4 ppm/degrees C at 80 degrees C. The temperature dependence of tau f could be evaluated by the average d tau fdT, which decreased monotonically from - 0.0206 ppm/degrees C2 to - 3.442 ppm/degrees C2 with increasing x from 0 to 1. The undesired temperature dependence of tau f should be common in microwave dielectric composites with near-zero tau f,W, which was determined by the nonlinear coefficient b2 and - tau 2f of the constituting phases, and expected to be suppressed by adopting suitable constituting phases with relatively low |b2| and |tau f,W|.