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High Quality Factor, Ultralow Sintering Temperature Li6B4O9 Microwave Dielectric Ceramics with Ultralow Density for Antenna Substrates

Zhou, Di, Pang, Li-Xia, Wang, Da-Wei, Qi, Ze-Ming, Reaney, Ian M.
ACS sustainable chemistry & engineering 2018 v.6 no.8 pp. 11138-11143
aluminum, bulk density, ceramics, dielectric properties, electrodes, prototypes, silver, temperature
Dense Li₆B₄O₉ microwave dielectric ceramics were synthesized at low temperature via solid-state reaction using Li₂CO₃ and LiBO₂. Optimum permittivity ∼ 5.95, quality factor ∼ 41 800 GHz and temperature coefficient of resonant frequency ∼ – 72 ppm/°C were obtained in ceramics sintered at 640 °C with a ultrasmall bulk density ∼2.003 g/cm³ (∼95% relative density, the smallest among all the reported microwave dielectric ceramics). Li₆B₄O₉ ceramics were shown to be chemically compatible with silver electrodes but reacted with aluminum forming Li₃AlB₂O₆ and Li₂AlBO₄ secondary phases. A prototype patch antenna was fabricated by tape casting and screen printing. The antenna resonated at 4.255 GHz with a bandwidth ∼279 MHz at −10 dB transmission loss (S₁₁) in agreement with simulated results. The Li₆B₄O₉ microwave dielectric ceramic possesses similar microwave dielectric properties to the commercial materials but much lower density and could be a good candidate for both antenna substrate and low-temperature cofired ceramics technology.