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

Manganese dioxide (alpha-MnO2) thin films have been explored as a cathode material for reliable glass capacitors. Conducting alpha-MnO2 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).4H(2)O) and acetic acid solvent (C2H4O2), which substantially reduced MnO2 phase stability, and resulted in Mn2O3 formation at pyrolysis temperature in air. The alpha-MnO2 structure was stabilized by Ba2+ insertion into a (2 x 2) oxygen tunnel frame to form a hollandite structure. With 15-20 mol% Ba addition, a conducting alpha-MnO2 thin film was obtained after annealing at 600-650 degrees C, exhibiting low electrical resistivity (similar to 1 Omega.cm), which enables application as a cathode material for capacitors. The hollandite alpha-MnO2 phase was stable at 850 degrees C, and thermally reduced to the insulating bixbyte (Mn2O3) phase after annealing at 900 degrees C. The phase transition temperature of Ba containing alpha-MnO2 was substantially higher than the reported transition temperature for pure MnO2 (similar to 500 degrees C).