Modification of NdNbO4 microwave dielectric ceramic by Bi substitutions

In the present work, Bi3+ was used to substitute for Nd3+ in the NdNbO4 ceramic and pure fergusonite solid solution was formed within 20 mol. % substitutions. Microwave dielectric permittivity of the (Nd1-xBix)NbO4 (x <= 0.2) ceramics increased linearly with x value due to the larger ionic polarizability of Bi3+ than Nd3+. Excellent microwave dielectric properties with a permittivity (epsilon(r)) similar to 22.5, a Qf (Q = quality factor, f = resonant frequency) similar to 50 000 GHz, and a TCF similar to-9 ppm/degrees C were obtained in the (Nd0.9Bi0.1)NbO4 ceramic. This method might work in other fergusonite-type rare-earth ortho-niobates.