Crystal Structures and Low Temperature Cofiring Ceramic Property of ($1-x$)(Li, RE)W2O8–$x$BaWO4 Ceramics ($\text{RE}=\text{Y}$, Yb)

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The crystal structures and low temperature cofiring ceramic (LTCC) microwave dielectric properties of ABW2O8 ($\text{A}=\text{Li}$, Na, Zn, $\text{B}=\text{Y}$, Yb, Mn, Fe) and the ($1-x$)LiYW2O8–$x$BaWO4 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 $\beta=94.2158(2)$°. The new materials LiREW2O8 ($\text{RE}=\text{Y}$, Yb) have highly positive $\tau_{\text{f}}$ values ($+63.8$ ppm/°C for $\text{RE}=\text{Y}$) in contrast to the negative $\tau_{\text{f}}$ values of BaWO4 and MgWO4. $\tau_{\text{f}}$ can be tailored to near zero by combining LiYW2O8 and BaWO4. The effects of sinter-additives on $\tau_{\text{f}}$, $Q f_{0}$ (GHz), and sintering temperature have been also characterized. The crystal structure has been analyzed by the Rietveld refinement method using neutron diffraction data.
2006-09-30