• PDF / 1,178,037 Bytes
• 7 Pages / 612 x 792 pts (letter) Page_size
• 76 Downloads / 350 Views

DOWNLOAD

REPORT

---

Thermal transport properties of decagonal quasicrystals and their approximants Petar Popčević1, Ante Bilušić1,2, Kristijan Velebit1 and Ana Smontara1 1 Institut za fiziku, Bijenička 46, 10000 Zagreb, Croatia 2 Faculty of Science, University of Split, Nikole Tesle 12, 21000 Split, Croatia ABSTRACT Transport properties (thermal conductivity, electrical resistivity and thermopower) of decagonal quasicrystal d-AlCoNi, and approximant phases Y-AlCoNi, o-Al13Co4, m-Al13Fe4, mAl13(Fe,Ni)4 and T-AlMnFe have been reviewed. Among all presented alloys the stacking direction (periodic for decagonal quasicrystals) is the most conductive one for the charge and heat transport, and the in/out-of-plane anisotropy is much larger than the in-plane anisotropy. There is a strong relationship between periodicity length along stacking direction and anisotropy of transport properties in both quasicrystals and their approximants suggesting a decrease of the anisotropy with increasing number of stacking layers. INTRODUCTION Since their discovery in 1982 by D. Shechtman [1], quasicrystals attract great attention due to their unique atomic structure and very interesting physical properties that result from it. They are mostly ternary alloys usually built on the basis of aluminum and transition metals. According to their crystal structure we distinguish two classes of quasicrystals: icosahedral and polygonal quasicrystals. In icosahedral quasicrystals [2], atoms are packed in clusters with icosahedral symmetry possessing quasiperiodic ordering along all three spatial directions. Among polygonal quasicrystals, we distinguish octagonal [3], decagonal [4] and dodecagonal [5] quasicrystals possessing quasiperiodic eightfold, tenfold and twelvefold symmetry axes, respectively, while they are periodically ordered along these symmetry axes. A possibility to grow crystals of decagonal phase of exceptional quality [6] makes them a good candidate for studying physical distinctions of periodic and quasiperiodic orderings on the same specimen. Besides that, a class of complex metallic alloys called approximants to the decagonal quasicrystals proved to be very useful in the task. Approximant phases are alloys possessing local atomic arrangements very similar to those in quasicrystals but retaining periodicity, which makes them an ordinary subject of theoretical investigation. It is well known that the degree of anisotropy of the transport properties of polygonal quasicrystals depends on the number of the quasiperiodic layers along one periodic unit [7]. Prior measurements of the electrical resistivity, thermopower [8] and thermal conductivity [9] have provided the motivation to thoroughly investigate the composition dependent transport properties (electrical resistivity (ρ), thermopower (S) and thermal conductivity (κ)) of decagonal quasicrystals and their approximants. EXPERIMENT In this study we investigated several approximant phases to the decagonal quasicrystals. Their structure can be viewed as stacking of pseudotenfold layers along the direction that