Simultaneous achievement of high quality factor and low sintering temperature in garnet ceramics

Two garnet-type microwave dielectric ceramics, Ca 3 M 2 GeV 2 O 12 (M = Zn, Cu), were successfully synthesized via the conventional solid-state reaction method. Their sintering behavior, microstructural characteristics, and microwave dielectric properties were systematically investigated. Phase purity was confirmed through XRD pattern analysis and Rietveld refinement, which indicated single-phase formation for both compositions. Scanning electron microscopy (SEM) observations revealed that both samples achieved dense microstructures with relative densities >96% at their respective optimal sintering temperatures. The Ca 3 Zn 2 GeV 2 O 12 ceramic sintered at 1120 °C exhibited excellent microwave dielectric properties with a relative permittivity ( ε r ) of 11.66 ± 0.2, a quality factor ( Q  ×  f ) of 61,849 ± 500 GHz, and a temperature coefficient of resonant frequency (τ f ) of −73.41 ± 0.7 ppm/°C. In comparison, the Ca 3 Cu 2 GeV 2 O 12 ceramic demonstrated a significantly lower sintering temperature of 930 °C and inferior dielectric properties, yielding ε r  = 10.4 ± 0.2, Q  ×  f  = 13,057 ± 500 GHz, and τ f  = −89.2 ± 0.7 ppm/°C. Furthermore, Ca 3 Cu 2 GeV 2 O 12 showed good chemical compatibility with silver electrodes, indicating its potential as a promising candidate material for low-temperature co-fired ceramic (LTCC) applications.