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Auxetics in spinels.

Auxetic materials laterally expand under uniaxial tension or laterally shrink under uniaxial compression. This unusual material property offers important advantages based on tunable material density, improved fracture resistance, hardness, shear modulus, shock and sound absorption, and so on. Possible applications for which auxetic behavior can be beneficially utilized range from strain amplifiers, optical pressure sensors, and tunable molecular sieves, and in the fields of nanotechnology and biomedicine for the development of, for example, artificial veins and muscles. In functional oxide materials the so-called molecular auxetic behavior is extremely rare. Now, in work with major potential consequences for the understanding of such materials, Professor M. Valant and co-workers have discovered this behavior in the Co[Fe.sub.2][O.sub.4] spinel structure. A Co[Fe.sub.2][O.sub.4] epitaxial thin film under compressive axial strain also reduces its cell dimensions in the transverse direction with a Poisson's ratio of -0.85; the hingelike honeycomb network in the spinel structure is identified as being responsible for this negative Poisson's ratio.

M. Valant et al., Adv. Funct. Mater. DOI: 10.1002/adfm.200901762
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Title Annotation:Materials Views
Author:Miller, Adrian
Publication:Plastics Engineering
Article Type:Brief article
Geographic Code:1USA
Date:Apr 1, 2010
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