Al-doped ZnO-Bi2O3-Co3O4 (ZBC) varistor ceramics were synthesized via the two-step method, and the influence of Al doping across the ‌completely‌ investigated 0.0–0.1 mol% range on microstructure and electrical properties was systematically examined. Characterization using XRD, SEM, and EDS revealed that Al3+ was effectively incorporated into the ZnO lattice, leading to lattice contraction and alterations in the material’s grain size. With increasing Al concentration from 0 to 0.075 mol%, the barrier height decreased to 2.16 eV. Correspondingly, the varistor voltage decreased from 86.8 to 49.7 V/mm and the nonlinear coefficient decreased from 39.6 to 30.6, consistent with barrier lowering. Complex impedance spectroscopy (CIS) demonstrates a reduction in both grain resistance (<InlineEquation ID="IEq1"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10854_2025_15961_Article_IEq1.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="21" /> </InlineMediaObject> <EquationSource Format="TEX">${R}_{g}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mi>g</mi> </msub> </math></EquationSource> </InlineEquation>) and grain boundary resistance (<InlineEquation ID="IEq2"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10854_2025_15961_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">${R}_{gb}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mrow> <mi mathvariant="italic">gb</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>) with rising Al content, reaching minimum values of 8.76 Ω and 153.14 kΩ at 0.1 mol% Al, which indicates that the resistance of Al-doped ZBC ceramics is mainly controlled by the <InlineEquation ID="IEq3"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10854_2025_15961_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">${R}_{gb}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mrow> <mi mathvariant="italic">gb</mi> </mrow> </msub> </math></EquationSource> </InlineEquation>. Thermally activated conduction analysis shows <InlineEquation ID="IEq4"> <InlineMediaObject> <ImageObject Color="BlackWhite" FileRef="10854_2025_15961_Article_IEq2.gif" Format="GIF" Height="19" Rendition="HTML" Resolution="72" Type="Linedraw" Width="28" /> </InlineMediaObject> <EquationSource Format="TEX">${R}_{gb}$</EquationSource> <EquationSource Format="MATHML"><math> <msub> <mi>R</mi> <mrow> <mi mathvariant="italic">gb</mi> </mrow> </msub> </math></EquationSource> </InlineEquation> follows Arrhenius behavior. The activation energies decrease from 0.35 to 0.25 eV with increasing Al concentration.

Effect of Al doping via a two-step process on grains and grain boundaries in ZnO varistor ceramics

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发表日期：

2025年10月21日

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Yu-Yan Shen,
Yong-Hui Zhou,
Yong Chen,
Mao-Hua Wang

摘要

Al-doped ZnO-Bi₂O₃-Co₃O₄ (ZBC) varistor ceramics were synthesized via the two-step method, and the influence of Al doping across the ‌completely‌ investigated 0.0–0.1 mol% range on microstructure and electrical properties was systematically examined. Characterization using XRD, SEM, and EDS revealed that Al³⁺ was effectively incorporated into the ZnO lattice, leading to lattice contraction and alterations in the material’s grain size. With increasing Al concentration from 0 to 0.075 mol%, the barrier height decreased to 2.16 eV. Correspondingly, the varistor voltage decreased from 86.8 to 49.7 V/mm and the nonlinear coefficient decreased from 39.6 to 30.6, consistent with barrier lowering. Complex impedance spectroscopy (CIS) demonstrates a reduction in both grain resistance ( ${R}_{g}$ $R_{g}$ ) and grain boundary resistance ( ${R}_{gb}$ $R_{gb}$ ) with rising Al content, reaching minimum values of 8.76 Ω and 153.14 kΩ at 0.1 mol% Al, which indicates that the resistance of Al-doped ZBC ceramics is mainly controlled by the ${R}_{gb}$ $R_{gb}$ . Thermally activated conduction analysis shows ${R}_{gb}$ $R_{gb}$ follows Arrhenius behavior. The activation energies decrease from 0.35 to 0.25 eV with increasing Al concentration.