Relation between ionic and electronic defects of Na 0.7MnO 2 bronze and its electrochemical properties

Abstract

This work presents the results of thermogravimetric, electrical conductivity and thermoelectric power measurements for a manganese bronze, Na 0.7MnO 2, under the conditions of thermodynamic equilibrium (600–1000 K) and at quenched defect structure. In addition, presented are the results of electrochemical studies on the manganese bronzes having different defect concentrations. It has been found that the manganese bronze has defects in the sodium sublattice and in the mangenese-oxygen sublattice. The deviation from stoichiometry in the manganese-oxygen sublattice introduces deep donor states. Thermoelectric power is negative in the whole temperature range studied and electrical conductivity has an activated character. It has been proved that close correlation exists between the electrical and electrochemical properties of the manganese bronze. The amount of sodium introduced by electrochemical intercalation depends on the concentration of electronic charge carriers in the starting material. The shape of the discharge curve for the Na/Na +/Na 0.7MnO 2 cell has been correlated with the character of the Fermi level changes of the cathode material with the concentration of electrons introduced by electrochemical intercalation.