| Summary: | In this work, novel MgCu<sub>2</sub>Nb<sub>2</sub>O<sub>8</sub> (MCN) ceramics were synthesized by the two-step sintering (TSS) technique, and the phase composition, crystal structures, and microwave dielectric properties were comprehensively studied. X-ray diffraction (XRD) and Raman analysis demonstrated that MCN ceramics are multi-phase ceramics consisting of MgNb<sub>2</sub>O<sub>6</sub> and CuO phases. X-ray photoelectron spectroscopy (XPS) was utilized to investigate the chemical composition and element valence of MgCu<sub>2</sub>Nb<sub>2</sub>O<sub>8</sub> ceramics. Scanning electron microscopy (SEM) analysis demonstrated dense microstructures in the MCN ceramics prepared at a sintering temperature of 925 °C. The microwave dielectric properties were largely affected by the lattice vibrational modes and densification level of the ceramics. The outstanding microwave dielectric properties of ε<sub>r</sub> = 17.15, <i>Q</i> × <i>f</i> = 34,355 GHz, and τ<i><sub>f</sub></i> = −22.5 ppm/°C were obtained for the MCN ceramics sintered at 925 °C, which are results that hold promise for low temperature co-fired ceramic (LTCC) applications.
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