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.
Electrical and thermal transport properties of intermetallic RCoGe2 (R = Ce and La) compounds
To investigate the electronic structure of the intermetallic compound CeCoGe2, we performed electrical resistivity (ρ), Seebeck coefficient (S), and thermal conductivity (κ) measurements in a temperature range of 10–300 K. For comparison, the non-magnetic counterpart LaCoGe2 is also studied. It is found that CeCoGe2 exhibits a broad maximum in the S(T) near 75 K, at which the sudden drop in the ρ(T) is observed. Temperature-dependent electrical resistivity and the Seebeck coefficient of CeCoGe2 can be described well by a two-band model, which reveals the signature of Kondo scattering in CeCoGe2. On the other hand, a typical metallic-like behavior is seen in the non-magnetic LaCoGe2 from the ρ(T) and S(T) studies. Analysis of the thermal conductivity indicates that the electronic contribution dominates thermal transport above 100 K in both CeCoGe2 and LaCoGe2. In addition, it is found that the variation in low-temperature lattice thermal conductivity of CeCoGe2 as compared to that of LaCoGe2 is most likely due to the phonon-point-defect scattering.
Variable-range hopping and the hall coefficient in Si:As
Abstract Conductivity and Hall measurements were made on Si:As samples on the barely-insulating side of the metal-insulator transition. Both conductivity and Hall coefficient obey variable-range hopping behavior ( ln σ ∝-( T 0 / T ) 1/4 and ln R H ∝( T 0 H / T ) 1/4 , with the quantity (T 0H /T 0 ) 1/4 equal to 0.63±0.02 in the limit of low magnetic field at the critical concentration, N c . This is the first experimental verification of the theoretical predictions of Gruenewald et. al. for R H in the variable-range hopping regime. (T 0H /T 0 ) 1/4 decreases somewhat with both increasing field and decreasing donor density. The prefactor for the Hall coefficient gives a value for lim (1/NeR H ) as N→N C consistent with the corresponding results in this system on the metallic side of the transition.