Microwave dielectric properties, microstructure, and bond energy of Zn3-xCoxB2O6 low temperature fired ceramics

Low temperature co-fired ceramics (LTCCs) technology plays an important role in modern wireless communication. Zn3-xCoxB2O6 (x = 0–0.25) low temperature fired ceramics were synthesized via traditional solid-state reaction method. Influences of Co2+ substitution on crystal phase composition, grain size, grain morphology, microwave dielectric properties, bond energy, and bond valence were investigated in detail. X-ray diffraction analysis indicated that the major phase of the ceramics was monoclinic Zn3(BO3)2. Solid solution was formed with Co2+ substituted for Zn2+ because no individual phase that contained Co was observed. An increase in the amount of Co2+ substitution changed average grain sizes, and regrowth of grains were observed with Co2+ substitution. Appropriate amount of Co2+ substitution improved densification. With changes in Co2+ substitution, bond energy of major phase and average bond valence of B–O were positively correlated to temperature coefficient of resonant frequency. The Zn2.927Co0.075B2O6 ceramic sintered at 875 °C for 4 h exhibited excellent microwave properties with εr = 6.79, Q × f = 140,402 GHz, and τf = −87.42 ppm/°C. This ceramic is regarded as candidate for LTCC applications.