<p>This study investigates Cr₂O₃/ZnO composite coatings as a surface-engineering strategy to enhance the electrical insulation performance of Al₂O₃ ceramics. Coatings containing 0.015, 0.025, 0.035, and 0.045&#xa0;mol ZnO (denoted Z1–Z4) were fabricated by screen printing and sintered to form dense Cr₂O₃-based layers partially integrated with the alumina substrate. Comprehensive microstructural, chemical, and electrical analyses reveal a strongly non-monotonic dependence of insulation behavior on ZnO loading. At low additions (Z1 and Z2), Zn²⁺ incorporates substitutionally into the corundum lattice, generating shallow traps and only modest dielectric enhancement. At intermediate content (Z3), the system enters a defect-saturated regime characterized by extensive oxygen-vacancy formation, pore coarsening, and heterogeneous interfaces, resulting in the highest trap density and strongest charge-retention capability, but also excessive leakage. At higher ZnO levels (Z4), segregation of wurtzite ZnO relieves lattice strain, reduces vacancy clustering, and interrupts defect-assisted conduction pathways. This structural recovery produces a more balanced electrical response, where moderated trap density is accompanied by reduced leakage and improved resistive stability, identifying Z4 as the most reliable composition for sustained high-field insulation rather than simply the maximum trap state. The results establish composition–structure–property guidelines for designing multi-oxide coatings with tunable defect chemistry and stable electrical performance.</p>