Structure determination of CaMnO3 and CaMnO2.5 by X-ray and neutron methods

✍ Scribed by K.R. Poeppelmeier; M.E. Leonowicz; J.C. Scanlon; J.M. Longo; W.B. Yelon

• Publisher: Elsevier Science
• Year: 1982
• Tongue: English
• Weight: 633 KB
• Volume: 45
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/0022-4596(82)90292-4

✦ Synopsis

Low-temperature synthesis of the oxygen-deficient compound CaMnO,., from polycrystalline CaMnO, preserves the existing structural framework of the oxidized precursor. The crystal structure of CaMnO,,, 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 = a, 2'j2, where a, is the simple cubic distance (-3.7 A) characteristic of the Mn4+-0'--Mn4+ framework in CaMnO,. The unique features of the structure are five-coordinate Mn3+ cations with nearly square pyramidal (-Cd,) coordination and ordered oxygen vacancies. The preparation, structure refinement, and noncubic distortions of single crystals of CaMnO, are also described. Attempts to transform single crystals of CaMnO, into CaMnO,., by well-ordered topotactic changes have not been successful.