Microstructure evolution, crystal structure, Raman analysis, bond characteristics and enhanced microwave dielectric properties of Zn1-xCuxZrNb2O8 solid solution ceramics

Abstract

The Structural factors of ceramic materials significantly affect microwave dielectric properties. Consequently, the structure–performance mechanism is essential for providing insight into material discovery and performance refinement. In the present work, Zn1-xCuxZrNb2O8 ceramics were synthesized through oxygen-assisted sintering procedures. The controversy of lattice vibrations was clarified and complete Raman vibration with complete mode assignments were provided for the first time through density functional theory and symmetry analysis. Intrinsic properties, including lattice energy, bond ionicity, thermal expansion coefficient, Raman vibrational states and bond energy, were calculated and the structure–performance relationships were established based on crystal structure refinement, density functional theory, chemical bond theory and Raman analyses. X-ray diffraction patterns and crystal structure refinement indicate a pure phase with the wolframite structure. The smaller ionic radii of Cu2+ ions led to a decrease in cell volume, which could account for the blueshift of the Ag mode at around 340 cm−1. Through Cu2+ substitution, the grain growth was further promoted and morphology evolution from polyhedral grain to rod shape was observed, which may be attributed to grain amalgamation. From chemical bond theory, Cu2+ substitution leads to the decrease in the dielectric constant, which is related to a decrease in the Nb–O bond ionicity (fiNb-O). The improvement in Q×f value is attributed to the high lattice energy of Nb–O bond (UNb–O), low FWHM at 845 cm−1 and large grain size. τf values are strongly impacted by the bond energies of the Zn/Cu–O bonds in the Zn1-xCuxZrNb2O8 ceramic crystals. Remarkably, microwave dielectric performance of the composition x = 0.06, sintered at 1175 °C, where εr = 27.9, Q×f = 73,200 GHz (@7.14 GHz) and τf = −40 ppm/°C, provide potential for millimeter-wave applications.