Properties of BaTiO₃–Al₂O₃ composite oxide films prepared by sol-gel coating and anodization

High-voltage etched aluminum foils were coated with BaTiO₃ (BT) films by vacuum infiltration using a sol. The specimens coated with the BT films were annealed at 450–550 °C for 10–90 min, and this procedure was repeated several times (n = 0, 1, 2, 4, and 8 cycles), after which the specimens were finally anodized at 100–500 V. The BT films coated on the high-voltage etched aluminum foils were crystallized when annealed at 550 °C for 30 min. The thickness of the BT-coated layer decreased after the anodization, proving that the BT-coated layers were decomposed by the anodization, likely contributing to the formation of a BT–Al₂O₃ (BT–Al) composite oxide layer between the inner BT-coated layer and the outer Al₂O₃ layer. The maximum specific capacitance (C_S) of the specimens was obtained after 4 cycles of BT coating. The specific capacitances of the BT-coated specimens were higher than those of the specimens without the BT-film coating. The withstanding voltages of the specimens were approximately 123, 330, and 545 V when the specimens were anodized at 100, 300, and 500 V, respectively. These results suggest the successful fabrication of BT–Al composite oxide films on high-voltage etched aluminum foils.