Glass-free LTCC microwave ceramic-Ca_1−x(La_0.5Na_0.5)_xWO₄

The structure and microstructure of the Ca_1−x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) ceramics were investigated using X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) method. The microwave dielectric properties of the ceramics were studied with a network analyzer at the frequency of about 10–14 GHz. Continuous solid solutions Ca_1−x(La_0.5Na_0.5)_xWO₄ (0.1 ≤ x ≤ 1.0) with Scheelite structure (space group: I4₁/a) could be densified at 850 °C/2 h. The dielectric permittivity increased slightly with the increase in substitution amount. The Q × f value decreased with the increase of x up to x = 0.5, and then increased with further increase of x. The Q × f value increased when the sintering temperature increased from 850 to 950 °C for the x < 0.5 compositions, whereas it decreased with the increase in sintering temperature for the x > 0.5 compositions. The τ _f value changed a little with the variation of x. All samples exhibited negative τ _f values. Addition of 30 mol% TiO₂ to the x = 0.9 composition improved the τ _f to −9.3 ppm/°C with ε_r = 14.4 and Q × f = 14,255 GHz after sintering at 850 °C/2 h. The chemical compatibility of Ca_0.1(La_0.5Na_0.5)_0.9WO₄ + 30 mol% TiO₂ composite with silver (Ag) powders was also investigated. The composite showed inert behavior with Ag when cofired at 875 °C for 2 h. However small amount of Na_0.86WO₃ impurity phase was detected in the co-fired specimen.