Cu-deficiency engineering in CaCu3 +Ti4O12 ceramics for high-reliability X7R capacitors and varistors

Achieving high dielectric reliability alongside nonlinear functionality in a single ceramic system remains a major challenge for next-generation electronic components. In the current work, we demonstrate that Cu deficiency in CaCu 3+ x Ti 4 O 12 ceramics, synthesized via a polymer-assisted pyrolysis route, offers a powerful strategy to simultaneously stabilize dielectric properties and enhance nonlinear response. Structural analysis confirmed dense, phase-pure microstructure, while dielectric testing revealed that Cu-deficient compositions exhibit outstanding thermal stability for ε′ and tan δ compared with their stoichiometric and Cu-rich counterparts. Notably, the CaCu 2.82 Ti 4 O 12 sample achieved ε′ ≈ 25,711 with tan δ = 0.021 and Δε′ < ±15% from −70 to 130 °C, thereby fully satisfying the stringent X7R standards. Nonlinear measurements further showed α values of 5.21–8.72 and breakdown fields of 1467–3151 V.cm⁻¹, underscoring their dual applicability in capacitors and varistors. This work highlights Cu deficiency as a scalable and industrially relevant strategy for engineering high-reliability dielectric ceramics, bridging the gap between multilayer ceramic capacitor (MLCC) technology and capacitor–varistor integration.