Electrochemistry of Manganese Dioxide in Lithium Nonaqueous Cells: IV . Jahn‐Teller Deformation of in

X‐ray diffractional (XRD) and electrochemical studies of prepared from heat‐treated electrolytic manganese dioxide (250°C, 7 days) were carried out in the rechargeable region of this material in lithium nonaqueous cells. The shape in the midpoint voltage curve between charge and discharge curves was observed to be quite different between the ranges and . XRD data indicated that the reaction proceeded in a homogeneous phase throughout the whole region. However, a discontinuous change in the orthorhombic unit cell parameters vs. x in plots was observed at . In order to explain such discontinuity in electrochemical and structural data, the Jahn‐Teller deformation of a octahedron in was considered assuming a possible octahedral linkage to form an orthorhombic unit cell. Our results indicated that the phase in the region is not the same as that in the region . The discontinuity observed in the electrochemical and structural data are ascribed to a phase transition at . The effect of the Jahn‐Teller distortion of octahedra upon the electrochemical behavior of several is discussed.