engleski

High pressure study of transport properties of CMA

An important question, in the field of giant- unit-cell complex metallic alloys (CMA), is which of the two coexisting physical length scales, the large (defined by the crystal periodicity) or the short (characterized by the distances between icosahedraly ordered atoms), plays the dominant role in determining the electrical properties of those materials [1]. An inside to this problem can be achieved by applying external hydrostatic pressure to the material sample and measure the temperature dependence of the electrical resistivity. Because the pressure brings the atoms closer, the overlap of the atomic potentials increases and the potential barriers between neighboring atoms are reduced. Consequently, one expects the enhancement of the electrical conductivity due to the reduction of the inter-atomic distances. In order to check this assumption, we conducted resistivity measurements on the A75Pd20Fe2 sample varying pressures from 1bar to 18 kbar, in the temperature range 4-300K. The sample was mounted into a self-clamped pressure cell, using petroleum as the pressure medium. The pressure was monitored in situ by a calibrated InSb pressure gauge. The relative change in volume  V as a function of the pressure change  p is estimated by evaluating  V/V =  p/E, where E is the material’ s elastic modulus. For a typical metal E is of the order 100 GPa, yielding  V/V 2% at 18 kbar. We observe that the resistivity drops significantly with pressure (from  300K (1bar) = 306µ ; ;  cm to  300K (17.8kbar) =284µ ; ;  cm. This is 7 % relative to the p=1bar value, whereas this reduction amounts to 8.5 % at 4 K). This behavior is consistent with the consideration that the resistivity of a CMA material is governed by the smaller of the two coexisting physical length scales. It can be thus concluded that the inter-atomic distances determine the electrical properties of CMA’ s, which is also valid for regular metals and alloys.

transport properties; pressure; complex metallic alloys

This work was supported in part by the 6th Framework EU Network of Excellence 'Complex Metallic Alloys' (Contract No. NMP3-CT-2005- 500140).