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<p>Cold sintering process (CSP) provides an effective method for controlling grain size through low-temperature densification in hundreds of ceramic materials, including ZnO-based ceramics. However, the interfacial layers, residual amorphous phases, and insufficient ionic solubility left by CSP hinder the overall performance of cold-sintered ZnO varistor ceramics. Here, thermal treatment is employed to assist cold-sintered ZnO varistor ceramics in addressing the defects arising from the CSP. Using CSP at 300&#xa0;°C, large-size ZnO varistor samples (40&#xa0;mm in diameter) with a relative density (<i>ρ</i><sub>r</sub>) of ~ 90% were achieved. Following the thermal treatment, the amorphous phase (e.g., Bi<sub>2</sub>O<sub>3</sub>, Y<sub>2</sub>O<sub>3</sub>, and Co<sub>2</sub>O<sub>3</sub>) was transformed into Bi-rich phases, which effectively filled pores and bonded loose grains, resulting in a notable increase in <i>ρ</i><sub>r</sub> to ~ 98% and an impressive Vickers hardness of 252&#xa0;HV. Meanwhile, the interfacial layer surrounding the ZnO grains transformed into high-resistance grain boundaries that are essential for high nonlinear ohmic properties. Specifically, the sample annealed at 850&#xa0;°C exhibited a high Schottky barrier (<i>Φ</i><sub>B</sub>) of 0.97&#xa0;eV and an ultra-low leakage current of 2.1&#xa0;μA&#xa0;cm<sup>−2</sup>, leading to a remarkable breakdown electric field (<i>E</i><sub>b</sub>) of 1573&#xa0;V&#xa0;mm<sup>−1</sup> and a high nonlinear coefficient (<i>α</i>) of 96. This work thus shows that combining CSP and thermal treatment provides a significant guideline for designing ZnO varistor ceramics with superior mechanical and electrical performances. </p> Graphical abstract <p></p>

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Cold sintering of large-sized ZnO varistor ceramics: unlocking superior non-ohmic behavior and breakdown strength via targeted thermal treatment

  • 期刊论文

  • 发表日期：

    2025年8月6日

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  • Qi Wang,
  • Xue-Tong Zhao,
  • Yong-Jian Xiao,
  • Yu-Chen Li,
  • Sheng-Lin Kang,
  • Jing Guo,
  • Kang-Ning Wu,
  • Xi-Lin Wang,
  • Jian-Ying Li,
  • Li-Jun Yang,
  • Rui-Jin Liao

摘要

Cold sintering process (CSP) provides an effective method for controlling grain size through low-temperature densification in hundreds of ceramic materials, including ZnO-based ceramics. However, the interfacial layers, residual amorphous phases, and insufficient ionic solubility left by CSP hinder the overall performance of cold-sintered ZnO varistor ceramics. Here, thermal treatment is employed to assist cold-sintered ZnO varistor ceramics in addressing the defects arising from the CSP. Using CSP at 300 °C, large-size ZnO varistor samples (40 mm in diameter) with a relative density (ρr) of ~ 90% were achieved. Following the thermal treatment, the amorphous phase (e.g., Bi2O3, Y2O3, and Co2O3) was transformed into Bi-rich phases, which effectively filled pores and bonded loose grains, resulting in a notable increase in ρr to ~ 98% and an impressive Vickers hardness of 252 HV. Meanwhile, the interfacial layer surrounding the ZnO grains transformed into high-resistance grain boundaries that are essential for high nonlinear ohmic properties. Specifically, the sample annealed at 850 °C exhibited a high Schottky barrier (ΦB) of 0.97 eV and an ultra-low leakage current of 2.1 μA cm−2, leading to a remarkable breakdown electric field (Eb) of 1573 V mm−1 and a high nonlinear coefficient (α) of 96. This work thus shows that combining CSP and thermal treatment provides a significant guideline for designing ZnO varistor ceramics with superior mechanical and electrical performances.

Graphical abstract