Microstructure, dielectric, non–ohmic, and humidity–sensing properties of Ca1+xCu2.9-xMg0.1Ti4O12 ceramics

Abstract

This study investigates a systematic investigation of Ca_1+xCu_2.9-xMg_0.1Ti₄O₁₂ (CCMTO) ceramic composites with x = 0 to 1.5, aimed at enhancing multifunctional performance through compositional tuning of the Ca/Cu ratio with fixed Mg doping. Increasing Ca²⁺ content leads to the formation of CCTO/CTO composite phases, grain refinement, and improved grain boundary control. Microstructural and phase analyses confirm that excess Ca promotes CTO formation, which contributes to a significant reduction in dielectric loss tangent (tanδ decreases from 0.146 to 0.025), while maintaining high dielectric permittivity (>10³). Impedance analysis reveals enhanced internal barrier layer capacitor effects and increased grain boundary resistance. The coexistence of Cu⁺/Cu²⁺ ions support semiconducting grain behavior and contributes to improve nonlinear properties, with Schottky barrier height increasing with x. Furthermore, the CCMTO ceramics exhibit strong humidity sensitivity, with capacitance changes exceeding 100% under RH variation, highlighting their potential as capacitive-type humidity sensors. These results demonstrate a promising strategy to overcome dielectric loss limitations in CCTO–based materials, offering an effective pathway toward integrated applications in capacitors, varistors, and capacitive humidity sensors.