Phase composition, crystal structure, complex chemical bond theory and microwave dielectric properties of high-Q materials in a (Nd1−xYx)NbO4 system

Abstract

In this paper, (Nd_1−xY_x)NbO₄ ceramics are prepared via a conventional solid-state reaction method and their microwave dielectric properties have been reported for the first time. The Rietveld refinement was used to investigate the crystal structure of (Nd_1−xY_x)NbO₄ ceramics. Based on the refined results, the NdNbO₄ ceramics have a monoclinic fergusonite structure (I2/a (15) space group, Z = 4). The XRD patterns present a single monoclinic phase of NdNbO₄ in the range of x = 0.02 to 0.1, with a further increase in the substitution content of Y³⁺ ions, few impurity phases are formed. In order to evaluate the correlations between complex chemical bond theory and microwave dielectric properties, the ionic polarization, lattice energy and bond energy were calculated using the refined lattice parameters and bond length. The effects of substituting Y³⁺ ions for Nd³⁺ ions on the microwave dielectric properties of the (Nd_1−xY_x)NbO₄ ceramics were also discussed. The increase in the dielectric constant ε_r is due to increasing the corrected theoretical dielectric constant ε_rc. For high relative density samples, the Q × f values and τ_f values are really dependent upon the calculated lattice energy and bond energy. High-quality factor microwave dielectric materials can be obtained with x = 0.08 in the (Nd_1−xY_x)NbO₄ system, and show excellent dielectric properties of ε_r = 19.87, Q × f = 81 100 GHz and τ_f = −18.84 ppm °C⁻¹.