The study of thermal and thermoelectric properties of quasicrystals, especially icosahedral phases, is of considerable interest in the context of searching for new materials with unique characteristics. Quasicrystals with aperiodic but long-range order exhibit properties different from traditional crystalline materials, which makes them promising for use in various fields, including thermoelectrics and thermal insulation. This work is devoted to the study of thermal conductivity, thermopower and electrical conductivity of the icosahedral quasicrystal Al62Cu25.5Fe12.5.
Experimental studies were conducted on Al62Cu25.5Fe12.5 samples obtained by melt quenching followed by annealing to form an icosahedral phase. Thermal conductivity was measured by a stationary method, thermoelectric power by a differential method, and electrical conductivity by a four-probe method in a wide temperature range.
Thermal and thermoelectric characteristics of the icosahedral quasicrystal i-AlCu25.5Fe12.5 were studied in the temperature range from 4.2 to 340 K. The obtained data were compared with similar characteristics of the icosahedral quasicrystal i-Al63Cu25Fe12.
The presented results for thermoelectric properties are in good agreement with the two-band model. Despite the fact that the presence of the valence band and the conduction band near the Fermi level causes the simultaneous presence of charge carriers of both signs, which allows classifying quasicrystals as semimetals, the temperature dependence of electrical conductivity is determined by the density of charge carriers, similar to a conventional semiconductor.
The phonon thermal conductivity exhibits a monotonic increase with temperature, characterized by a small maximum near 25 K, followed by a minimum at about 70 K and a further increase. The minor maximum in the phonon thermal conductivity can be interpreted as a transition from dominant scattering by tunnel states of unknown nature to a regime where quasi-periodic Umklapp processes play a significant role.
The results showed that the icosahedral quasicrystal Al62Cu25.5Fe12.5 has low thermal conductivity, comparable to that of amorphous materials. This is due to the complex structure of the quasicrystal, which leads to strong phonon scattering. The thermopower of the sample has a positive sign and linearly depends on temperature, indicating p-type conductivity. The value of the thermopower is large enough, which makes this material promising for use in thermoelectric devices. Electrical conductivity exhibits a semiconductor character with an activation energy corresponding to the energy gap near the Fermi level.
The obtained results indicate that the icosahedral quasicrystal Al62Cu25.5Fe12.5 is an interesting material for thermoelectric applications due to its low thermal conductivity and relatively high thermoelectric power. Further studies aimed at optimizing the composition and structure of the material can lead to the creation of efficient thermoelectric energy converters.
Author: A Bilušić , A Smontara , JC Lasjaunias , J Ivkov , Y Calvayrac
Institute: Institute of Physics, HR-10001, P.O. Box 304, Zagreb, Croatia, Centre for Ultra-Low Temperature Research, Laboratory associated with the Joseph Fourier University, CNRS, 38042 Grenoble, France, cCECM-CNRS, 15 rue G, Urbain, 94407 Vitry-sur-Seine, France