Crystal structures, chemical bonds, and microwave dielectric properties of ZnCu2Nb2O8 ceramics

ZnCu2Nb2O8 (ZCN) ceramics were prepared by solid-state reaction technology for investigating the influences of different sintering temperatures (S.T.) on crystal structure, microscopic morphology, and microwave dielectric properties. The characterization results of X-ray diffraction (XRD), Rietveld refinement, and transmission electron microscope (TEM) identify formation of ZnCu2Nb2O8 phase with triclinic structure and P1 space group. Scanning electron microscopy (SEM) demonstrates that proper sintering temperature can promote growth of grains, revealing the maximum relative density of 98.9% for ZCN ceramics sintered at 920 degrees C. Inverse correlation is observed between dielectric constant (er) and Raman shift of A1g(O) near 805 cm-1. The relative density, lattice energy (Ub) and full width at half maximum (FWHM) are correlated with the quality factor (Q x f) of ZCN ceramics. Based on P-V-L theory, it is confirmed that Nb-O bond plays dominant role in ionicity, lattice energy, and bond energy, which has significant impact on the dielectric properties than other bonds. Notably, the ZCN ceramics by sintering at 920 degrees C, present optimal microwave dielectric properties: epsilon r = 18.56, Q x f = 47,776 GHz, and zf = -16.3 ppm/degrees C. Furthermore, The co-firing ZCN ceramics with Ag demonstrates good compatibility, highlighting the potential candidacy of ZCN ceramic as low temperature co-fired ceramic (LTCC).