Synthesis and electrical properties of stabilized manganese dioxide (α-MnO₂) thin-film electrodes

Manganese dioxide (α-MnO₂) thin films have been explored as a cathode material for reliable glass capacitors. Conducting α-MnO ₂ thin films were deposited on a borosilicate glass substrate by a chemical solution deposition technique. High carbon activities originated from manganese acetate precursor, (Mn(C₂H₃O₂) ₂·4H₂O) and acetic acid solvent (C ₂H₄O₂), which substantially reduced MnO ₂ phase stability, and resulted in Mn₂O₃ formation at pyrolysis temperature in air. The α-MnO₂ structure was stabilized by Ba²⁺ insertion into a (2 × 2) oxygen tunnel frame to form a hollandite structure. With 15-20 mol% Ba addition, a conducting α-MnO₂ thin film was obtained after annealing at 600-650°C, exhibiting low electrical resistivity (∼1 Ω·cm), which enables application as a cathode material for capacitors. The hollandite α-MnO₂ phase was stable at 850°C, and thermally reduced to the insulating bixbyte (Mn₂O₃) phase after annealing at 900°C. The phase transition temperature of Ba containing α-MnO ₂ was substantially higher than the reported transition temperature for pure MnO₂ (∼500°C).