Low-temperature synthesis of the oxygen-deficient compound CaMnO2.5 from polycrystalline CaMnO3 preserves the existing structural framework of the oxidized precursor. The crystal structure of CaMnO2.5 was determined using neutron powder diffraction data analyzed by the Reitveld profile refinement method. The structure of the reduced phase can be described by the orthorhombic distortion (a0 + b0 2) 2 = ac 2 1 2, where ac is the simple cubic distance (∼3.7 Å) characteristic of the Mn4+O2-Mn4+ framework in CaMnO3. The unique features of the structure are five-coordinate Mn3+ cations with nearly square pyramidal (∼C4v) coordination and ordered oxygen vacancies. The preparation, structure refinement, and noncubic distortions of single crystals of CaMnO3 are also described. Attempts to transform single crystals of CaMnO3 into CaMnO2.5 by well-ordered topotactic changes have not been successful.
ASJC Scopus subject areas
- Inorganic Chemistry
- Physical and Theoretical Chemistry
- Materials Chemistry