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The symmetry of Fe2O3 and Cr2O3 (monoclinic) is simpler than the official (trigonal) one

What is it about?

Both alpha-Fe2O3 and alpha-Cr2O3 crystals have a special direction [110] which is perpendicular to the hexagonal [001] axis. The rotation by 180 deg. around this special direction [110] is a symmetry operation of the crystal. The monoclinic distortion of alpha-Fe2O3 is described with "positive sign" while that of and alpha-Cr2O3 is described with "negative sign".

Why is it important?

These observations may indicate the existence of some kinds of symmetry in alpha-Fe2O3 and alpha-Cr2O3 crystals which are not yet understood nowadays.

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The following have contributed to this page:
Radoslaw Przenioslo
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