Effects of (Li_0.5Nb_0.5)³⁺ co-substitution on microwave dielectric characteristics of MgAl₂O₄ ceramics

Abstract

Nominal compositions MgAl_2−x(Li_0.5Nb_0.5)_xO₄ (x=0–0.20) microwave dielectric ceramics were synthesized via the traditional solid-state reaction. The crystal structural characteristics, crystalline phases, and microwave dielectric properties were investigated. Rietveld refinement results showed that MgAl₂O₄ and Mg₅Nb₄O₁₅ form a stable two-phase system. Densification of the specimens decreases monotonically with the increase of (Li_0.5Nb_0.5)³⁺ content when sintered at 1550 °C. The variation tendency of quality factor (Q_f) is closely related to the densification, packing fraction and covalency. Likewise, the bond valence of the Al-site is responsible for the temperature coefficient of resonance frequency (τ_f). MgAl_2−x(Li_0.5Nb_0.5)_xO₄ ceramic with x=0.04 can be well densified by sintering at 1550 °C for 4 h and exhibits optimum microwave dielectric properties with ε_r=8.21, Q_f=81600 GHz, and τ_f=−94×10⁻⁶ °C⁻¹.

Keywords

microwave dielectric ceramics / co-substitution / MgAl₂O₄ ceramic

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