TY - JOUR
T1 - The crystal structure of Cr8O21 determined from powder diffraction data: Thermal transformation and magnetic properties of a chromium-chromate-tetrachromate
AU - Norby, P.
AU - Nørlund Christensen, A.
AU - Fjellvåg, H.
AU - Nielsen, M.
PY - 1991
Y1 - 1991
N2 - 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) Å, α = 106.36(1), β = 95.73(1) and γ = 77.96(1)°) and was refined in the space group P1. 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.
AB - 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) Å, α = 106.36(1), β = 95.73(1) and γ = 77.96(1)°) and was refined in the space group P1. 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.
KW - Materialers atomare struktur og egenskaber
U2 - 10.1016/0022-4596(91)90193-L
DO - 10.1016/0022-4596(91)90193-L
M3 - Journal article
SN - 0022-4596
VL - 94
SP - 281
EP - 293
JO - Journal of Solid State Chemistry
JF - Journal of Solid State Chemistry
IS - 2
ER -