DFT and experimental approaches of effect of (Al, Ga) doping ions on colossal dielectric properties of ZnO ceramic.

The dielectric properties of (Ga, Al)-doped ZnO ceramics were studied by density functional theory (DFT) and experimental aspectes. In the first, the combustion method was used to prepare the pristine ZnO and Ga-, Al-doped, and codoped ZnO nanopowders, then calcined nanoparticles were characterized by x-ray diffraction technique (XRD), and field emission scanning electron microscopes (FE-SEM). Finally, the synthesized nanopowders were sintered and the dielectric properties of the ceramics were measured to reveal the effect of Ga and Al doping on ZnO. In case of the density functional theory (DFT) calculation which is conducted on the Vienna Ab initio Simulation Package (VASP) using generalized gradient approximation with Hubbard parameter (GGA + U), 4 × 2 × 2 supercells of pure ZnO and Ga-, Al-doped and codoped ZnO were modeled. The supercells were optimized, and then the density of states (DOS) were investigated. From the DFT results, doping Al and Ga shifts the Fermi level to higher states. Additionally, the semiconductive behavior of ZnO changes to a metallic character after Al and Ga doping. Thus, we found from the DFT calculation that it is possible that Al and Ga doping can improve the dielectric properties of ZnO. According to the results, we have successfully synthesized (Al, Ga)-doped ZnO ceramics. Interestingly, Ga-doped ZnO ceramics exhibited colossal dielectric response with low tanδ (about 0.83) and high ε′ (around 40,623). Ga doping in ZnO benefits dielectric properties more than Al doping and co-doping due to Ga's closer ionic radius to Zn, which minimizes lattice distortion and defects. This leads to improved stability of the ZnO lattice, reducing the formation of oxygen vacancies and enhancing dielectric performance. Therefore, it can be summarized that this work succeeds in the enhancement of dielectric properties of ZnO by Ga doping. As a result, ZnO could be a higher-efficiency dielectric material when it is doped by Ga. [ABSTRACT FROM AUTHOR]