NiZrNb2O8 microwave dielectric ceramics were prepared by an optimized sol-gel method using Nb2O5 center dot nH(2)O as a precursor. The thermal decomposition behavior of the Nb2O5 center dot nH(2)O was characterized by different thermal analysis and thermogravimetry (DTA/TG). Nanoscale NiZrNb2O8 particles with wolframite structure were obtained at about 950 degrees C. Regarding the microwave dielectric properties of NiZrNb2O8 ceramics, significant dependence has been verified with the sintering conditions, microstructure and compositions. The correlation between NiZrNb2O8 crystal structure and microwave dielectric properties was investigated from the analysis result of crystal structure refinement, chemical bonding ionicity and lattice energy based on the theory of valence. The relative density, dielectric constants, quality factors and temperature coefficients of the resonant frequency of NiZrNb2O8 ceramics sintered at 1100 degrees C reached 5.585 g/cm(3), 29.31, 22985 GHz and -24.96 ppm/degrees C, respectively. (C) 2018 Elsevier B.V. All rights reserved.