Glass-Free LTCC Microwave Ceramic-(La0.5Na0.5)1-x(Li0.5Nd0.5)xWO4

Ceramics (La0.5Na0.5)(1-x)(Nd0.5Li0.5)(x)WO4 (0.1 <= x <= 0.7) have been successfully designed as promising dielectric materials for LTCC applications. The structure and microstructure of the compounds were investigated by 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 (La0.5Na0.5)(1-x)(Nd0.5Li0.5)(x)WO4 (0.1 <= x <= 0.7) were formed as expected in the whole composition range. They could be sintered into dense ceramic (similar to 96% theoretical density) at 800 degrees C/2 h. All samples exhibit single Scheelite structure (I4(1)/a) phase. The dielectric constant increased, whereas the Q x f value decreased continuously, with the increase of x. The tau(f) value changed from negative to positive with the increase of x, and near zero value of -1.4 ppm/degrees C could be obtained at x = 0.3 composition. Combined excellent microwave dielectric properties with epsilon(r) = 12.7, Q x f = 23 518 GHz and tau(f) = -1.4 ppm/degrees C could be obtained when sintered at 800 degrees C/2 h. The chemical compatibility of (La0.5Na0.5)(0.7)(Nd0.5Li0.5)(0.3)WO4 ceramic with silver (Ag) powders was also investigated. Some Ag substituted for Li and formed Li2WO4 impurity phase, although isolated Ag still existed in the co-fired specimen (800 degrees C/2 h).