Topotactic Two‐Phase Reaction of Ruthenium Dioxide (Rutile) in Lithium Nonaqueous Cell

Electrochemical and x‐ray diffraction studies were carried out for the reduction of having rutile structure in propylene carbonate/1,2‐dimethoxyethane (1:1) solution. was topotactically reduced to , drawing an L‐shaped voltage curve. X‐ray diffraction examinations of the reduced indicated that (tetragonal; ,) was transformed to (orthorhombic; , , ) via an intermediate phase having a tetragonal lattice (, ). The reaction was reversible, i.e., was electrochemically oxidized to via an intermediate phase. Although three phases coexisted during the reduction of and oxidation of , the reaction was classified as a topotactic two‐phase reaction in which an intermediate phase existed between the and phases. Hysteresis was observed, even in plots of the open‐circuit voltages (OCV) vs. the reduction degree, when the cell was cycled. The reaction mechanism of is discussed, with emphasis on one characteristic of a topotactic two‐phase reaction. The mechanochemical aspects on the reaction are also described.