Defect and microstructural engineering in (Al, Li) co-doped ZnO ceramics by spark plasma sintering for giant dielectric performance

High-permittivity ceramics are essential for compact capacitors, high-capacitance-density components, and energy-efficient electronics. However, their practical implementation is often limited by the difficulty of simultaneously achieving giant permittivity, low dielectric loss, and operational stability. Herein, (Al 0.5 Li 0.5 ) x Zn 1− x O ceramics with high dopant content were fabricated by spark plasma sintering (SPS)to simultaneously regulate bulk defects and grain boundary barriers. The optimized x  = 0.2 ceramic exhibits colossal permittivity over a broad frequency range, with a relative permittivity of 11710 and a dielectric loss of 0.101 at 100 Hz. Microstructure and impedance analyses reveal that the colossal permittivity of the co-doped ZnO ceramics originates from an internal barrier layer capacitor (IBLC) response arising from the electrical contrast between semiconducting ZnO grains and resistive grain boundaries. The former are associated with donor-related defect chemistry and the reducing SPS environment, whereas the resistive grain-boundary response is associated with Al 3+ enrichment and ZnAl 2 O 4 -related secondary phases. Furthermore, first-principles calculations indicate that Li + -related defects and Li + –Al 3+ complexes induce local lattice distortion and charge redistribution, while finite-element simulations illustrate modified breakdown-channel evolution. This work demonstrates a defect–grain boundary co-regulation strategy for designing ZnO-based giant dielectric ceramics suitable for compact and reliable capacitive applications.