Complex chemical bond theory, Raman spectra and microwave dielectric properties of low loss ceramics NdNbO4-xAl2O3

In this work, low loss microwave dielectric materials of NdNbO4-x wt% Al2O3 ceramics were prepared via a solid-state reaction method. The complex chemical bond theory, phase composition, standard deviation (sigma) of the bond angles, microstructures, microwave dielectric properties and vibrational phonon modes were investigated. Microscopic analysis showed that sintered specimens presented single monoclinic fergusonite phase. The Rietveld refinements and Raman spectra were used to evaluate the correlation between the complex chemical bond theory and the microwave dielectric properties. With an increase of Al2O3 content, the Raman shift of A(g) (331 and 808 cm(-1)) toward to the bigger value direction and the FWHM of A(g) (331 and 808 cm(-1)) decrease, which lead to a decrease in bond ionicity and increase in lattice energy. The microwave dielectric properties of NdNbO4-x wt% Al2O3 exhibit closely relationship with the complex chemical bond theory. The variation trend of dielectric constant was accordance with the bond ionicity. The Q x f value and tau(f) value were mainly dependence on the lattice energy and bond energy, respectively. Fine microwave dielectric properties for NdNbO4-3 wt% Al2O3 ceramic was obtained with epsilon(r) = 18.1, Q x f = 54,700 GHz (9.1 GHz), tau(f) = -0.51 ppm/degrees C sintered at 1150 degrees C for 4 h.