Small-angle neutron scattering of alkali metals at moderate uniaxial pressure and low temperature

This paper reports on the development of a cryostat for neutron small-angle scattering experiments on alkali metals under uniaxial compression in a temperature range from 5 K to room temperature. The investigation was motivated by earlier observations of 'premartensitic' anomalies in metallic lithium and potassium which seem to suggest that nuclei of a low-temperature phase might be generated in the undercooled bcc structure either by cooling alone or by additional mechanical deformation. Cooling to 120 K in lithium and to 5 K in potassium, respectively, without applied load produced only very slight changes in the SANS patterns. However, after uniaxial compression of 3% at these temperatures anisotropic scattering patterns developed, suggesting the formation of small particles embedded in the bcc matrix whose orientation is related to the deformation direction.