Grain growth suppression and electrical performance Optimization in Ho3+-Doped CCTO ceramics for Capacitor–Varistor Integration

• Excellent dielectric and non-ohmic properties were achieved in Ca o . 85 Ho o . 1 o Cu 3 Ti 4 O 12 ceramics sintered at 1020 °C for 10 h. • Tanδ=0.049 and ε’= 7477 were attained in the Ca 0.85 Ho 0.10 Cu 3 Ti 4 O 12 ceramic. • The Ca o . 85 Ho o . 1 o Cu 3 Ti 4 O 12 ceramic exhibits outstanding X7R-grade performance, with ε′ = 7477, tanδ = 0.049, and Δε′ ≤ ±15% over −60 °C to 130 °C. • The highest α = 46.45 with E b = 8321 V.cm -1 was achieved. Ho 3+ -doped Ca 1-1.5x Ho x Cu 3 Ti 4 O 12 ( x= 0–0.10) ceramics were synthesized via a sol–gel method and sintered at 1020 °C and 1050 °C. This was done to investigate the effects of Ho 3+ substitution on structural, dielectric, and nonlinear electrical properties. Substitution of Ho 3+ at Ca 2+ sites led to significant enhancement in dielectric performance by suppressing grain growth through solute drag and pinning mechanisms, thereby increasing grain boundary resistance. The x =0.10 sample sintered at 1020 °C exhibited a dielectric constant (ε′) of 7477, low dielectric loss (tanδ=0.049), and excellent thermal stability (Δε′ ≤ ±15%) over the temperature range of −70 °C to 130 °C, meeting X7R capacitor standards. Nonlinear electrical properties were also improved, with a nonlinearity coefficient (α) of 46.45 and breakdown field (E b ) of 8321 V/cm. At 1050 °C, grain coarsening resulted in a higher dielectric constant (∼8360) and further enhanced varistor performance (α=16.27, E b =6042 V/cm). These findings highlight the potential of Ho 3+ doping in tailoring the multifunctional properties of CCTO ceramics for advanced capacitor and varistor applications.