Temperature independent low firing [Ca_0.25(Nd_1-xBi_x)_0.5]MoO₄ (0.2 ≤ x ≤ 0.8) microwave dielectric ceramics

A scheelite structured [Ca_0.25(Nd_1-xBi_x)_0.5]MoO₄ (0.2 ≤ x ≤ 0.8) ceramics were prepared via solid state reaction method. All the ceramics can be well densified below 780 °C. As x value increased from 0.2 to 0.8, microwave dielectric permittivity increased from 14.0 to 27.8, Qf (Q = quality factor = 1/dielectric loss; f = resonant frequency) value decreased from 42,000 GHz to 19,000 GHz, and TCF shifted from −50 ppm/^oC to +18 ppm/^oC. The best microwave dielectric properties with permittivity between 23.54 and 23.56, Qf value between 24,000 GHz–21,000 GHz and TCF value ∼ −8 ppm/^oC in wide temperature range 25 °C–130 °C were obtained in x = 0.6 ceramic. This work showed that Bi played an important role to modify the TCF from negative to positive value in scheelite materials and this result further accelerate the application of scheelite materials in low temperature co-fired ceramics (LTCC) technology.