Effects of lanthanides on structural and dielectric properties of NdNbO4-LnNbO4 ceramics

Recently, lanthanide niobates have attracted significant attentions in multi-functional materials. Herein a series of fergusonite structure-related (1-x)NdNbO4-xLnNbO4 (Ln = Yb, Er, Ho, Dy, Gd and Ce; 0.02 ≤ x ≤ 0.08) ceramics were prepared via conventional solid-state reaction method and the microwave dielectric properties were systematically discussed. The X-ray diffraction, Raman spectra were employed to investigate the crystal structure. Obtained results indicate that the ceramic samples present single monoclinic phase belong to the space group of I2/a. Microwave dielectric behaviors shown that the permittivity (εr) and the quality factor (Q × f) were influenced by the relative density, and the temperature coefficients of resonant frequency (τƒ) value kept the same variation tendency with the Nb-site bond valence. Furthermore, Far-IR and bond energy study evidenced the Ln-O oscillations dominated the main dielectric polarization and system stability. Good microwave dielectric properties, with εr ~ 20.88, Q × f ~ 66,510 GHz (at 8.60 GHz) and τf ~ − 36.59 ppm/°C, were obtained in 0.94NdNbO4-0.06YbNbO4 ceramics when sintered at 1250 °C for 4 h. The (Nd0.94Yb0.06)NbO4 might be potential candidate for the applications of modern microwave devices.