Transport Property Studies on Icosahedral Systems: Rapidly Quenched Al-V, Al-Mn, and Al-Fe-Mn.
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TRANSPORT PROPERTY STUDIES ONICOSAHEDRAL SYSTEMS: Al-Mn, AND Al-Fe-Mn. K. V. RAO, N. KARPE, R. MALMHALL*,
RAPIDLY QUENCHED Al-V,
H. U. ASTRUM, AND H. S. CHENt
Dept. o4 Solid State Physics6, Royal Inst. o4 Technology, Stockholm, Sweden. * ASEA Research and Innovation, S-721 78 V&6terAs, Sweden. t Visiting Scientis6t from: AT& T-Befl Laboratorin, Mm'ay Hitt, NJ07974,USA.
ABSTRACT We report the first Hall, and electrical resistivity study on rapidly The Hall coefficient is found to be quenched icosahedral Al-based alloys. negative and remains so for i(Al-Mn) alloys even for higher Mn concentrations. The magnitude and temperature coefficient of the electrical resistivity behaviour in these alloys is similar to those observed for amorphous metallic alloys. Thus, the conduction process in i(Al-based alloys) is essentially electronic but with a carrier mobility an order of magnitude smaller than that known for crystalline aluminium. INTRODUCTION Rapid solidification technology, RST, has opened a new, exciting, and rapidly expanding field of considerable scientific and technological interest. A metallurgist has for the first time a capability to expand over a wider range the manipulation of composition and internal structure of metals. With this new 'molecular switch' totally new alloys with unique combination of properties At higher rates of quenching (106 K/sec) one obtains the are now feasible. amorphous or 'glassy' state which is considered to represent a new state of matter with remarkable mechanical and physical properties. The interpretation of the properties of these metallic glasses poses a particular challenge to the theorist, since the understanding of solids hitherto has been based on crystalRecently, on a rather fundamental line solids with translational invariance. basis there have been some theoretical evidence that the local structure of liquids and metallic glasses can be described as icosahedral [1]. Icosahedral co-ordination shells have been shown [2] to lead naturally to peaks at the appropriate distances in the radial distribution function, even obtaining the 'split-second-peak' structure commonly observed via X-ray scattering in metallic glasses. That crystals can never have five-fold axes of symmetry has been a part of doctrine of crystallography ever since Federov classified the admissible symmetry groups in 1895. Recently, this myth has lost grounds with the identification of icosahedral point group symmetry in the metastable phase of rapidly quenched Al-Mn alloys [3] which argues for long range orientational It now seems quite plausible order but with no translational periodicity. to consider the transformations from gaseous to the liquid to crystalline phases as a continuous change towards lower symmetry, i.e: from a spherical environment of the gas to the icosahedral one in liquid and then to the crystalline environment of a lower symmetry [4]. It is thus natural that most of the theoretical studies on these exciting new class of 'quasicrystals' have focussed on their symmetry properties, si
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