Electrical Properties of Ag-In-(Yb,Ca) Quasicrystals and Their Approximants
- PDF / 363,238 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 103 Downloads / 214 Views
LL7.9.1
Electrical Properties of Ag-In-(Yb,Ca) Quasicrystals and Their Approximants Daisuke Tetsuka, Ryuji Tamura and Shin Takeuchi Department of Materials Science and Technology, Tokyo University of Science, Noda, Chiba 278-8510, Japan ABSTRACT We report the electrical resistivity of the ternary Ag-In-(Yb,Ca) quasicrystals (QCs) together with those of their 1/1 and 2/1 cubic approximants. The temperature coefficient of the resistivity (TCR) is negative and nearly the same for the QCs and the 2/1 approximants suggesting that the coherence length of the conduction electrons in the QCs is comparable to the lattice parameter of the 2/1 approximants, i.e., ~2.5 nm. On the other hand, both positive and negative values of TCR are observed for the 1/1 approximants depending on the annealing temperature. Taking into consideration the occurrence of positive TCR in the binary Cd-(Yb,Ca) 1/1 approximant, the latter phenomenon suggests that the negative TCR of the ternary 1/1 approximants is due to chemical disorder between Ag and In, and the chemical disorder is possibly reduced when annealed at low temperatures.
INTRODUCTION The ternary icosahedral (i) Cd-Ag-(Yb,Ca) quasicrystals (QCs) found by Guo et al. [1] are obtained by replacing Cd of the binary Cd-(Yb,Ca) QCs [2,3] by the same atomic concentration of Ag and In. These new ternary QCs are of great interest with respect to their electronic transport since the binary QCs exhibit peculiar electrical properties [4,5], and comparison between the binary and the ternary QCs of similar atomic structure has now become possible. It is expected that the replacement of Cd by Ag and In may introduce chemical disorder on the Cd site of the binary Cd-(Yb,Ca) QCs and the electrical resistivity may be very sensitive to the introduction of such disorder. In addition, disorders are likely to increase in equilibrium at elevated temperatures and for this reason the resistivity of the ternary Ag-In-(Yb,Ca) QCs might be also sensitive to the annealing condition such as the annealing temperature. In this paper, we will present the electrical resistivity of the ternary Ag-In-(Yb,Ca) QCs as a function of temperature and discuss the influence of annealing, i.e., equilibrium disorders, on the electronic transport. The results of their related crystalline approximants such as 1/1-1/1-1/1 and 2/1-2/1-2/1 approximants will be also presented for comparison, and the difference of the
LL7.9.2
electronic transport will be discussed in terms of the approximation degree. EXPERIMENTAL DETAILS High-purity elements Ag(99.999wt.%), In(99.999wt.%), Yb(99.9wt.%) and Ca(99.99wt.%) were alloyed in an arc-furnace at nominal compositions of Ag42In42(Yb,Ca)16 and Ag43In43(Yb,Ca)14 in order to obtain QCs and 1/1-1/1-1/1 approximants, respectively. For the 2/1-2/1-2/1 approximant, a single phase was obtained at nominal compositions Ag42.5In42.5Ca15 and Ag42.25In42.25Yb15.5. Furthermore, Ag42In42Yb8Ca8 and Ag43In43Yb7Ca7 alloys were prepared in order to investigate the effect of partial chemical disorder on the elec
Data Loading...
