Icosahedral and approximant phases in a Mg-Ga-Al-Zn alloy and their electrical resistivities

It has been found in a Mg Ga-Al-Zn alloy that an icosahedral phase produced by melt-spinning transforms to the 1/1 cubic approximant of the icosahedral phase at 653 K and successively to the 2/1 cubic approximant at around 668 K upon heating. Structural relations of the two approximant phases to the icosahedral phase are discussed, in the framework of the projection scheme, on the basis of X-ray diffraction data.Electrical resistivities have been measured from 4·2 K to 280 K for single-phase samples of the icosahedral and approximant phases. The icosahedral phase and the 2/1 approximant one show similar behaviour, in which the resisitivity is ∼ 120 μω2 cm at 4-2 K and the temperature coefficient is negative. In contrast, the 1/1 approximant phase shows a relatively smali resistivity value of ∼ 60 μω cm at 4-2 K and a positive temperature coefficient. Changes in the resistivity accompanied by the phase transformations have been confirmed by measuring the resistivity upon heating the melt-spun sample up to above the transformation temperatures.