m ) for 4 Volt Secondary Lithium CellsAbstract
(
in hexagonal setting) whose parent structure was a solid solution of 
and 
was prepared and examined in a nonaqueous lithium cell. The oxidation of 
and reduction of
proceeded reversibly in the voltage range above 3.5 V. X‐ray diffractional examinations indicated the reaction proceeded in a topotactic manner. During the oxidation of 
, the 
dimension elongated from 14.1 to 14.5 Å and the 
shortened from 2.84 to 2.80 Å almost linearly as a function of 
until 
reached about 0.5. Consequently, the lattice volume remained almost invariable at 98.5 Å3. Further oxidation resulted in the shrinkage of the 
dimension and the elongation of the 
. Detained open‐circuit voltage measurements also were carried out. The open‐circuit voltages varied as a function of 
following a hyperbolic tangent curve, not an S‐shaped Nernstian curve. The composition‐dependent open‐circuit voltage curve together with the XRD observations indicated that the reaction proceeded in a homogeneous phase. Differences and similarities of the solid‐state redox reactions among 
, 
, and 
were discussed.