Modification of NdNbO ₄ microwave dielectric ceramic by Bi substitutions

In the present work, Bi ³⁺ was used to substitute for Nd ³⁺ in the NdNbO ₄ ceramic and pure fergusonite solid solution was formed within 20 mol. % substitutions. Microwave dielectric permittivity of the (Nd _{1- x} Bi _x )NbO ₄ (x ≤ 0.2) ceramics increased linearly with x value due to the larger ionic polarizability of Bi ³⁺ than Nd ³⁺ . Excellent microwave dielectric properties with a permittivity (ε _r ) ~22.5, a Qf (Q = quality factor, f = resonant frequency) ~50 000 GHz, and a TCF ~−9 ppm/°C were obtained in the (Nd _0.9 Bi _0.1 )NbO ₄ ceramic. This method might work in other fergusonite-type rare-earth ortho-niobates.