Low-Temperature Thermodynamic and Thermal-Transport Properties of Decagonal Al65Cu20Co15
| Autor: | E. Felder, M. A. Chernikov, K. Edagawa, U. Gubler, Andrea Bianchi, H. R. Ott |
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| Rok vydání: | 1996 |
| Předmět: | |
| Zdroj: | Physical Review Letters. 77:1071-1074 |
| ISSN: | 1079-7114 0031-9007 |
| DOI: | 10.1103/physrevlett.77.1071 |
| Popis: | Decagonal quasicrystals share structural properties of periodically and quasiperiodically structured matter. They are periodic along the tenfold symmetry axis and quasiperiodic in the plane perpendicular to it. Since the recent discovery of thermodynamically stable decagonal quasicrystals in the Al-Cu-Co and Al-Ni-Co systems [1,2], it has become possible to study properties of both periodically and quasiperiodically structured matter along different directions of one single sample. The growth of fairly large single grains has been reported for Al-Cu-Co and Al-Ni-Co decagonal quasicrystals [2,3], which is of primary importance for reliable investigations of the anisotropic behavior. For decagonal quasicrystals in these systems, strong anisotropies of electrical- [4] and thermal- [5] transport properties, and also of the optical conductivity [6] have experimentally been established. Below we describe our results of measurements of the specific heat CpsT d and of the thermal conductivities l p sT d and l q sTd along the periodic direction and along a direction in the quasiperiodic plane, respectively, of high-quality single-grained samples of decagonal AlCu-Co in varying temperature ranges between 0.06 and 105 K. This set of data contains information on the specific heat, to our knowledge not investigated before for decagonal quasicrystals. It also extends the temperature range of previous investigations of thermal-transport properties in these materials [5] by more than 2 orders of magnitude, thus providing evidence for the conceptually different lattice conduction of heat via l p sTd and l q sT d, defined above. The ingot with a nominal composition Al65Cu20Co15 was synthesized from 99.999% pure aluminum, 99.9985% pure copper, and 99.997% pure cobalt by arc melting suitable amounts of the constituents to a single piece and remelting it several times. The resulting ingot was remelted again at 1100 ‐ C in an alumina crucible sealed under vacuum inside a silica ampoule, cooled to 920 ‐ C at the rate 2 ‐ C per h, annealed at 920 ‐ C for 24 h, and subsequently cooled to room temperature. Faceted decaprisms up to 1.5 mm in diameter and up to 6 mm in length were cut from the ingot using spark erosion. Two decaprisms with approximate dimensions 2.9 3 1.5 3 0.4 and 2.0 3 0.6 3 0.4 mm 3 have been selected for our experiments. Their naturally formed facets were polished to remove possible surface contaminations. A high degree of quasicrystalline order was confirmed by electron diffraction experiments. Laue photographs taken on both samples have confirmed that they are single grains. The smaller sample has been used for measurements of the thermal conductivity l p sT d along the tenfold symmetry axis, while the larger grain has been used for measuring l q sT d along a direction in the quasiperiodic plane and also for the specific heat CpsT d measurements. The thermal conductivity lsT d was measured using a standard steady-state heat-flow technique monitoring the temperature gradient along the sample. The specific heat CpsTd was measured using a conventional relaxation-type method. The temperatures in the range between 0.06 and 1 K were reached using a dilution refrigerator, and we used 3 He and 4 He cryostats for temperatures between 0.35 and 3 K, and above 1.5 K, respectively. Figure 1(a) shows the complete set of our results of the specific heat CpsTd measured in the temperature range between 1.5 and 17 K, plotted on logarithmic scales. Our CpsTd data between 1.5 and 4.5 K, shown in Fig. 1( b) as CpyT vs T 2 , are well fitted by |
| Databáze: | OpenAIRE |
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