Neumann bands

Microstructural examinations revealed deformation twins (Neumann bands) in metal grains at wasted surfaces. The surfaces in these areas have a jagged, undercut profile. 

In BCC structures, the twin plane is (112) and the twinning shear is in the direction [llT]. The only common example of such twins is in a-iron (ferrite) deformed by impact, where they occur as extremely narrow twin bands called Neumann bands. It should be noted that, in cubic lattices, both 112 and 111 reflection twinning produce the same orientation relationship however, they dilfer in the interatomic distances produced, and an FCC lattice can twin by reflection on 111 with less distortion than on 112, while for the same reason 112 is the preferred plane for BCC lattices. 

A. Hunsche and P. Neumann Quantitative measurement of persistent slip band profiles and crack initiation. Acta metallurgica, 34(2) 207-217, 1986. 

Dienes Y, Durben S, Karpati T, Neumann T, Englert U, Nyulaszi L, Baumgaitner T (2007) Selective tuning of the band gap of pi-conjugated dithieno[3,2-b 2, 3 -d]phospholes toward different emission colors. Chem Eur J 13 7487... 

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