Crystal Structures and Low Temperature Cofiring Ceramic Property of (1-x)(Li, RE)W2O8–xBaWO4 Ceramics (RE=Y, Yb)

The crystal structures and low temperature cofiring ceramic (LTCC) microwave dielectric properties of ABW2O8 (A=Li, Na, Zn, B=Y, Yb, Mn, Fe) and the (1-x)LiYW2O8–xBaWO4 binary system have been characterized. LiYW2O8 has a new type of crystal structure in-between the wolframite (MgWO4) and scheelite (BaWO4) structures: the space group P2 and the lattice parameters of a=9.9815(5), b=5.7913(3), c=5.0058(2) Å, and β=94.2158(2)°. The new materials LiREW2O8 (RE=Y, Yb) have highly positive τf values (+63.8 ppm/°C for RE=Y) in contrast to the negative τf values of BaWO4 and MgWO4. τf can be tailored to near zero by combining LiYW2O8 and BaWO4. The effects of sinter-additives on τf, Qf0 (GHz), and sintering temperature have been also characterized. The crystal structure has been analyzed by the Rietveld refinement method using neutron diffraction data.