Simultaneous improvement of permittivity and nonlinear properties and loss tangent reduction through semi-wet route in NiO-modified CaCu3Ti4O12 ceramics: grain boundaries effect

Abstract

In this study, NiO-modified CaCu₃Ti₄O₁₂ (CCTO–xNiO) ceramics were successfully synthesized via a semi-wet route, achieving simultaneous enhancement of dielectric and nonlinear properties while reducing dielectric losses. Unlike conventional solid-state methods, this approach offers improved control over grain morphology, leading to a significant reduction in energy dissipation. The impact of NiO doping (x = 0.01, 0.06, 0.15, 0.2) on the microstructure and dielectric characteristics of CCTO ceramics was systematically investigated. SEM analysis revealed a grain size increase from 2.53 µm (x = 0) to 11.46 µm (x = 0.06), followed by a decrease to 1.83 µm (x = 0.15) and 1.03 µm (x = 0.2), demonstrating the effect of NiO on grain growth inhibition. A minor quantity of NiO (x = 0.06) promoted grain growth, leading to enhanced dielectric and electrical properties. The 6% NiO sample exhibited the highest permittivity of 1.2 × 10⁵ at 1 kHz, while the 15% NiO sample displayed the lowest dielectric loss (~ 0.02 at 1 kHz), a higher breakdown voltage (~ 4640 V·cm⁻¹), and an enhanced nonlinear coefficient (~ 5.55), confirming its improved insulating performance. These enhancements are attributed to a synergistic effect between NiO doping and grain boundary modifications, as explained by the Schottky barrier and internal barrier layer capacitor (IBLC) models. This study provides new insights into microstructure-property relationships in CCTO ceramics, paving the way for the development of advanced dielectric materials with optimized performance for energy storage and capacitor applications.