Influence of (Al_1/3W_2/3)⁵⁺ co-substitution for Nb⁵⁺ in NdNbO₄ and the impact on the crystal structure and microwave dielectric properties

Abstract

NdNb1-x(Al1/3W2/3)xO4 (x = 0.03-0.07) solid solution compounds were synthesized and characterized via solid-state reaction. XRD patterns reveal the formation of a single fergusonite phase, and the dependence of microwave dielectric properties on its structural characteristic was investigated based on Rietveld refinements together with complex chemical bond theory. The variation of dielectric constant is attributed to the Nb/Al1/3W2/3-O bond ionicity. The grain size and total lattice energy are both associated with quality factor, and the temperature coefficient is affected by oxygen and bond valence of the Nb site. Infrared reflectivity spectrum analysis illustrated that the permittivity is primarily due to ion polarization in the microwave frequency region. Notably, the following properties of NdNb1-x(Al1/3W2/3)xO4 (x = 0.04) ceramics were obtained: εr ∼ 19.04, Q × f ∼ 58 219 GHz and τf ∼ -41.14 ppm/°C.