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<p>Alumina (Al₂O₃) is a promising candidate for microwave dielectric ceramics due to its exceptional quality factor (Qf ~ 333,000&#xa0;GHz). This study investigates the influence of additions of titania (TiO₂) and annealing treatments on the dielectric properties of polycrystalline Al₂O₃. The dielectric properties of Al₂O₃-x wt% TiO₂ (x = 2.5, 5, 7.5, 10) were evaluated after various heat treatment conditions. The optimal composition, Al₂O₃-7.5 wt% TiO₂, achieved notable properties when sintered at 1400&#xa0;°C for 8&#xa0;h: a relative permittivity (ε<sub>r</sub>) of 10.73 and a quality factor-frequency product (Qf) of 126,347&#xa0;GHz at 13.814&#xa0;GHz. Specifically, subsequent annealing at 1000&#xa0;°C for 5&#xa0;h adjusted the temperature coefficient of frequency (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="43939_2025_429_Article_IEq1.gif" Format="GIF" Height="14" Rendition="HTML" Resolution="72" Type="Linedraw" Width="17" /> </InlineMediaObject> <EquationSource Format="TEX">\(\:{\tau}_{f}\)</EquationSource> </InlineEquation>) to + 1.25 ppm/°C, near zero. The study reveals that the thermal treatment induces the decomposition of Al₂TiO₅ into Al₂O₃ and TiO₂, accompanied by titanium redistribution. Characterization using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and dielectric measurements established correlations between the microstructure and properties. This work provides a scalable framework for designing ultra-stable millimeter-wave ceramics, particularly for 5G/6G resonators and satellite communication systems, where minimal signal delay and thermal drift are critical.</p>

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Zero temperature coefficient microwave alumina ceramics via TiO₂ doping and post sinter annealing

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月17日

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  • Yuting Xiao,
  • Millicent Appiah,
  • Burhan Ullah,
  • Yixin Yang,
  • Wayne D. Kaplan,
  • Daniel Q. Tan

摘要

Alumina (Al₂O₃) is a promising candidate for microwave dielectric ceramics due to its exceptional quality factor (Qf ~ 333,000 GHz). This study investigates the influence of additions of titania (TiO₂) and annealing treatments on the dielectric properties of polycrystalline Al₂O₃. The dielectric properties of Al₂O₃-x wt% TiO₂ (x = 2.5, 5, 7.5, 10) were evaluated after various heat treatment conditions. The optimal composition, Al₂O₃-7.5 wt% TiO₂, achieved notable properties when sintered at 1400 °C for 8 h: a relative permittivity (εr) of 10.73 and a quality factor-frequency product (Qf) of 126,347 GHz at 13.814 GHz. Specifically, subsequent annealing at 1000 °C for 5 h adjusted the temperature coefficient of frequency ( \(\:{\tau}_{f}\) ) to + 1.25 ppm/°C, near zero. The study reveals that the thermal treatment induces the decomposition of Al₂TiO₅ into Al₂O₃ and TiO₂, accompanied by titanium redistribution. Characterization using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and dielectric measurements established correlations between the microstructure and properties. This work provides a scalable framework for designing ultra-stable millimeter-wave ceramics, particularly for 5G/6G resonators and satellite communication systems, where minimal signal delay and thermal drift are critical.