Electrical and thermal transport properties of icosahedral Al70Pd22.5(Re1−xMnx)7.5 quasicrystals
This work presents measurements of the electrical resistivity (ρ), Seebeck coefficient, and thermal conductivity (κ) of icosahedral Al70Pd22.5(Re1−xMnx)7.5 quasicrystals from 10to300K. A series of quasicrystals was prepared with x=0, 0.1, 0.2, 0.3, 0.5, 0.6, 0.8, and 1.0 to systematically study the effect of substitution. The electrical resistivity increases as the temperature decreases, suggesting a semiconductinglike behavior in these alloys. The room-temperature values of the Seebeck coefficient vary from −5μV∕K to +65μV∕K, showing a significant dependence on the value of x. However, κ exhibits a rather weak composition dependence in the temperature range investigated. The room-temperature dimensionless thermoelectric figure of merit (ZT) of this system is optimized at x=0.1. With further appropriate heat treatments, high ZT is presumably available at elevated temperatures in the Al70Pd22.5(Re0.9Mn0.1)7.5 sample.
Thermal and thermoelectric properties of icosahedral Al62Cu25.5Fe12.5 quasicrystal
Abstract Experimental results on thermal and thermoelectric properties of icosahedral i-Al 62 Cu 25.5 Fe 12.5 quasicrystal in temperature range 4.2–340 K are examined, and comparison with icosahedral i-Al 63 Cu 25 Fe 12 quasicrystal is made. The results of thermoelectric properties can be consistently explained by a two-band model. Although the picture that overlaps with the valence and the conduction bands at Fermi level is responsible for the coexistence of both types of carriers enables us to describe quasicrystals as semi-metals, the situation in which temperature variation of the electrical conductivity is determined by that of carrier density is essentially the same as in the case of normal semiconductor. The phonon thermal conductivity increases monotonically with temperature showing a shallow maximum at about 25 K, followed by a minimum around 70 K, and a subsequent increase. The shallow maximum in phonon thermal conductivity could be interpreted as a crossover from the regime of a dominant scattering on tunneling states of an unspecified nature to the regime where quasiperiodic Umklapp processes are important.
Low-temperature thermal properties of icosahedral Al-Re-Pd
We report measurements of the thermal conductivity λ(T) and the specific heat Cp(T) of icosahedral Al70Re8.6Pd21.4 at low temperatures. Below 1 K, the behaviour of the quasilattice thermal conductivity λph(T) is compatible with the scattering of vibrational excitations involving tunnelling states and grain boundaries. The specific heat Cp(T) contains a small linear contribution γ T. Our λph(T) results indicate that a substantial part of γ T may be attributed to the excitations of tunnelling states. Below 0.4 K Cp(T) increases with decreasing T and at the lowest temperatures it varies as T−2, suggestive of an interaction of the quadrupolar moments of 185Re and 187Re nuclei with the gradient of electric fields induced by their neighbours.