Effects of ZrO2 sol concentration on microstructure and electrical properties of ZrO2-Al2O3 dielectrics formed on Al foils

The effects of ZrO2 sol concentration on the microstructure and electrical properties of ZrO2-Al2O3 dielectrics on etched Al foils are studied. The experiment is carried out by coating the surface of etched Al foils with ZrO2 sol with a series of concentrations and anodizing in the 2-methyl-1,3-propanediol (MPD)-boric acid electrolyte at 700, 800, and 900 V. The increase in the thickness of the ZrO2-coated layer with increasing ZrO2 sol concentration causes a reduction in the total thickness of dielectrics. The tetragonal-to-monoclinic ZrO2 phase change can be induced by anodization and the increase in the crystalline size of tetragonal ZrO2. The Zr-Al-O composite layer after anodization exhibits a microstructure that is a combination of the microstructures of separated high-permittivity crystalline ZrO2 and amorphous high-resistivity Al2O3. The optimal ZrO2 sol concentration is 1.3 M, and the specific capacitances increased by 38% for 700 V, 40% for 800 V, and 66% for 900 V compared with those of non-coated samples.