Phase Composition, Crystal Structure and Microwave Dielectric Properties of Nb-Doped Yttrium Aluminum Garnet Ceramics

The Y3Al5-xNbxO12 (0 ≤ x ≤ 0.06) garnet ceramics were prepared by solid-state reaction method. The effects of Nb5+ substitution on the phase composition, microstructure and microwave dielectric properties were investigated. All samples retained the yttrium-aluminum garnet solid solution form until x up to 0.06 at which YNbO4 secondary phase precipitated. The doping of Nb2O5 improved the grain development and enhanced the physical properties of the ceramics under the sintering condition of 8 h at 1700 °C. Specifically, with the substitution of Nb5+, the degree of micromorphology improvement and quality factor first increased and then decreased, with a maximum value at x = 0.015. Finally, the best combination of microwave dielectric properties was obtained, i.e., εr = 10.79, Q×f = 165,478 GHz, τf = -31.7 ppm/°C. This study provides a theoretical basis for the further expansion and application of yttrium aluminum garnet in the microwave field. Keywords: Yttrium Aluminum Garnet ceramics, Nb2O5, microwave dielectric properties.