Influence of bond valence on microwave dielectric properties of (1-x)CaWO4-xLnNbO4 (Ln=Nd, Sm) solid solutions

Microwave dielectric properties of (1-x)CaWO4-xLnNbO(4) (Ln=Nd, Sm) ceramics were investigated as a function of LnNbO(4) content (0.05 <= x <= 0.30). Solid solutions with scheelite structure were obtained with LnNbO(4) content LIP to x=0.3 of Ln=Nd and/or x=0.2 of Ln=Sm, respectively. The unit-cell volume was decreased with the increase of B-site bond valence. For the solid solutions, dielectric constant (K) was slightly increased with LnNbO(4) content and K of the specimens with NdNbO4 was higher than that of SmNbO4. This result was due to the larger dielectric polarizability of NdNbO4 (17.02 angstrom) than SmNbO4 (16.75 angstrom). The quality factor (Qf) was dependent on the microstructure of the specimens. Temperature coefficient of resonant frequency (TCF) increased with the increase of LnNbO(4) content due to the decrease of the differences between A-site and B-site bond valence in ABO(4) scheelite.