Microwave dielectric properties of (1-x)Ba5Nb4O15-xBaNb2O6 mixtures

The mixture behavior and microwave dielectric properties of (1 - x)Ba5Nb4O15-xBaNb(2)O(6) ceramics were studied by means of X-ray powder diffraction and a network analyzer. 0.17Ba(5)Nb(4)O(15)-0.83BaNb(2)O(6) samples sintered at 1250degreesC for 2h. exhibit excellent microwave dielectric properties: dielectric constant (epsilon(r)) = 35.2, quality factor (Q x f) = 59300 GHz and temperature coefficient of resonant frequency (tau(f)) = 0 ppm/degreesC. The epsilon(r) and tau(f) of mixtures could he predicted by the appropriate mixing relation. but deviated slightly from calculated values. This was attributed to dissimilar microstructural grain morphologies of the Ba5Nb4O15 and BaNb2O6 end members. In the mixtures. higher Q x f was obtained rather than Ba5Nb4O15 and BaNb2O6, due to pore reduction. Also. the mixture behavior of low-fired Ba5Nb4O15-BaNb2O6 wall discussed. A major contributor to microwave dielectric properties of low-fired samples is the low temperature phase, hexagonal BaNb2O6.