The crystal structure of Cr8O21 determined from powder diffraction data: Thermal transformation and magnetic properties of a chromium-chromate-tetrachromate

Abstract Thermal decomposition of CrO3 was utilized to prepare a powder sample of the chromium oxide usually designated Cr3O8. Combined information from powder diffraction data using synchrotron, conventional X-ray, and neutron radiation allowed determination of the structure. The structure is triclinic (a = 5.433(1), b = 6.557(1), c = 12.117(2) A, α = 106.36(1), β = 95.73(1) and γ = 77.96(1)°) and was refined in the space group P 1 . The true composition of the compound is Cr8O21. There are two distinct types of chromium atoms in the structure, which may be designated the oxidation numbers (III) and (VI), respectively. The structure is built from pairs of edge-sharing Cr(III)O6 octahedra linked together by Cr(VI)O4 tetrahedra to form sheets. The sheets are then linked together by tetrachromate groups (Cr(VI)4O13) to form a three-dimensional structure. Thus, the chromium oxide may be described as Cr(III)2(Cr(VI)O4)2(Cr(VI)4O13). The magnetic properties of Cr8O21 were investigated in the temperature range 5 to 300 K. Above 100 K the compound is paramagnetic. Magnetic susceptibility data indicate a transition to antiferromagnetism around 100 K, but only vague indications for additional magnetic reflections were found with neutron powder diffraction.

[1]  G. Pawley.  EDINP, the Edinburgh powder profile refinement program , 1980 .

[2]  R. Schwartz,et al.  The Products of Thermal Decomposition of Chromium Trioxide1,2 , 1952 .

[3]  J. S. Stephens,et al.  The crystal structure of (CrO3) , 1970 .

[4]  R. Koksbang,et al.  Reversibility of the electrochemical lithium insertion in “Cr3O8”—comparison with LiCr3O8 , 1991 .

[5]  Y. Takeda,et al.  Amorphous chromium oxide; A new lithium battery cathode , 1987 .

[6]  R. Newnham,et al.  Refinement of theαAl2O3, Ti2O3, V2O3and Cr2O3structures* , 1962 .

[7]  S. Gronowitz,et al.  The Crystal Structure of Cr5O12. , 1965 .

[8]  M. Lehmann,et al.  Structure determination by use of pattern decomposition and the Rietveld method on synchrotron X‐ray and neutron powder data; the structures of Al2Y4O9 and T2O4 , 1987 .

[9]  Lars Eriksson,et al.  TREOR, a semi-exhaustive trial-and-error powder indexing program for all symmetries , 1985 .

[10]  M. Y. Abyaneh.  Formulation of a general model for nucleation and growth of electrodeposits , 1991 .

[11]  Y. Takeda,et al.  Characteristics of amorphous chromium oxide as a cathode for lithium organic solvent cells , 1985 .

[12]  R. Schöllhorn,et al.  Chromium oxides as cathodes for secondary high energy density lithium batteries , 1977 .

[13]  Y. Takeda,et al.  Chromium oxides as cathodes for lithium cells , 1983 .

[14]  J. Besenhard,et al.  Characteristics of molybdenum oxide and chromium oxide cathodes in primary and secondary organic electrolyte lithium batteries. Part II. Transport properties , 1983 .

[15]  J. Besenhard,et al.  Characteristics of molybdenum oxide and chromium oxide cathodes in primary and secondary organic electrolyte lithium batteries I. Morphology, structure and their changes during discharge and cycling , 1982 .

[16]  Ε. E. Newnham,et al.  Refinement of the a Al2O3, Ti2O3, V2O3 and Cr2O3 structures , 1962 .

[17]  T. A. Hewston,et al.  Magnetic and structural studies of Cr2O5 and Cr3O8 , 1984 .

[18]  A. F. Wells,et al.  Structural Inorganic Chemistry , 1971, Nature.

[19]  L. Ehrenberg,et al.  Formation of Chromium Oxides in the Cr2O3-CrO3 Region at Elevated Pressures up to 4 Kilobar. , 1968 .

[20]  Y. Takeda,et al.  Rechargeable Lithium/Chromium Oxide Cells , 1984 .

[21]  P. Löfgren.  The crystal structure of rubidium tetrachromate, Rb2Cr4O13 , 1973 .

[22]  J. Møller,et al.  The Crystal Structure of KCr3O8. , 1958 .