The effects of various transition metal dopants on the electrical and thermal transport properties of Fe1-xMxSi alloys (M= Co, Ir, Os) are reported. The maximum thermoelectric figure of merit ZTmax is improved from 0.007 at 60 K for pure FeSi to ZT = 0.08 at 100 K for 4% Ir doping. A comparison of the thermal conductivity data among Os, Ir and Co doped alloys indicates strong electron-phonon coupling in this compound. Because of this interaction, the common approximation of dividing the total thermal conductivity into independent electronic and lattice components (κTotal = κelectronic + κlattice) fails for these alloys. The effects of grain size on thermoelectric properties of Fe0.96Ir0.04Si alloys are also reported. The thermal conductivity can be lowered by about 50% with little or no effect on the electrical resistivity or Seebeck coefficient. This results in ZTmax = 0.125 at 100 K, still about a factor of five too low for solid-state refrigeration applications.
The simplified bandstructure introduced by Mazurenko et al to model FeSi is used to analyze the singlet semiconductor to ferromagnetic metal transition in the isoelectronic isostructural alloys, FeSi$_{1-x}$Ge$_x$. The complex bandstructure of the alloy is replaced by an alternating chain of doubly and singly degenerate atoms to represent Fe and Si/Ge respectively. The former(latter) form narrow(broad) bands with a substantial hybridization between them. A substantial onsite repulsion including a Hund's rule coupling is introduced on the Fe sites. The mean field phase diagram contains a first …
We report electron tunneling spectroscopy studies on single crystalline FeSi sample performed for the case of homogeneous tunnel junction contacts and for the case of counter electrodes made from Pt-Rh alloy. Our results reveal that while the tunneling spectroscopy in the configuration with Pt-Rh tip is preferably sensitive to the d-partial density of states and to the indirect energy gap, the FeSi-FeSi type of tunnel junction yields spectroscopic information on the c-partial density of states and on the direct gap in FeSi.
Solid solution between nonmagnetic narrow gap semiconductor FeSi and diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with long-range helical magnetic ordering, for a wide range of intermediate concentration. We report various interesting magnetic properties of these alloys, including low temperature re-entrant spin-glass like behaviour and a novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya interaction in the magnetic response of these non-centrosymmetric alloys is discussed.
In this work, we have investigated the electronic structure and thermoelectric properties of quaternary heusler alloy, FeRuTiSi, using first principle DFT tools implemented in WIEN2k and BoltzTraP code. Electronic structure calculations using TB-mBJ potential shows appearance of flat band at the conduction band edge, thus electron in conduction band have the large effective mass (me*), and therefore mainly contribute for negatively large value of Seebeck coefficient (S). This alloy has indirect band gap of 0.59 eV, and shows the n-type transport behavior. Under the constant relaxation time app…
Analysis on very detailed measurements of resistivity ($ ρ$) and thermoelectric power (S) of magnetic impurity (Co) substituted iron silicide (FeSi) has been presented in this report. The impurity valence electrons of Co dominate the whole physical properties at low temperatures below 35 K, below the critical concentration x$_{c}$. The negative thermopower and the positive slope in the resistivity at low temperatures are exotic and show that the system is not entirely insulator below the critical concentration of MIT (x$_{c}$). So, due to the external impurity electrons, the system's magnetic …
To understand the unexpectedly high thermoelectric performance observed in the thin-film Heusler alloy Fe$_2$V$_{0.8}$W$_{0.2}$Al, we study the magnon drag effect, generated by the tungsten based impurity band, as a possible source of this enhancement, in analogy to the phonon drag observed in FeSb$_2$. Assuming that the thin-film Heusler alloy has a conduction band integrating with the impurity band, originated by the tungsten substitution, we derive the electrical conductivity $L_{11}$ based on the self-consistent t-matrix approximation and the thermoelectric conductivity $L_{12}$ due to mag…
On the basis of density functional theory and semi-classical Boltzmann theory, we have investigated the structural, elastic, electronic, optical and thermoelectric properties of 18--valence electron count rhodium based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The absence of imaginary frequencies in the phonon dispersion curve for these system verifies that they are structurally stable. RhTiP is ductile in nature, while others are brittle. The alloys are found to be semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. Our calculations suggest these mate…
We investigate the high temperature thermoelectric properties of Heusler alloys Fe2-xMnxCrAl (0<x<1). Substitution of 12.5% Mn at Fe-site (x = 0.25) causes a significant increase in high temperature resistivity (\r{ho}) and an enhancement in the Seebeck coefficient (S), as compared to the parent alloy. However, as the concentration of Mn is increased above 0.25, a systematic decrement in the magnitude of both parameters is noted. These observations have been ascribed (from theoretical analysis) to a change in band gap and electronic structure of Fe2CrAl with Mn-substitution. Due to absence of …
Ternary half Heusler alloys are under intense investigations recently towards achieving high thermoelectric figure-of-merit (ZT). Of particular interest is the ZrNiPb based half Heusler (HH) alloy where an optimal value of ZT = 0.7 at 773 K has been achieved by co-doping Sn and Bi at Pb site. In this work, we identify an excellent ZT of 1.3 in ZrNi1+xPb0.38Sn0.6Bi0.02 (x= 0.03, at 773 K) composite alloy. This is achieved by synergistic modulation of electronic as well as thermal properties via introduction of minor phase of full Heusler (FH) in the HH matrix through compositional tuning approa…
Here, we have investigated the thermoelectric properties of FeMnScGa alloy by combined use of full potential linearized augmented plane-wave (FP-LAPW) method and Boltzmann transport theory implemented in Wien2K and BoltzTraP code, respectively. Using the TB-mBJ potential, half-metallic nature is clearly observed with energy band gap of ~0.41 eV for down spin channel. Transport coefficients in 200-1000 K temperature range are investigated under the constant relaxation time approximations (tau=10-14 s). Total contributions to the Seebeck coefficients from up and dn-spin channels are estimated by…
Regularities and features in the behavior of electrical and magnetic properties of Co$_2$FeZ (Z = Al, Si, Ga, Ge, Sn, Sb) half-metallic ferromagnetic Heusler alloys
本文测量 Co$_2$FeZ 系列 Heusler 合金的电阻率、磁化和 Hall 效应，揭示其随 Z 元素原子序数变化的电磁关联及不同温区的电阻散射规律。
We report measurements of the thermoelectric power (TEP) for a series of Pb(1-x)Tl(x)Te crystals with x = 0.0 to 1.3%. Although the TEP is very large for x = 0.0, using a single band analysis based on older work for dilute magnetic alloys we do find evidence for a Kondo contribution of 11 - 18 uV/K. This analysis suggests that Tk is ~ 50 - 70 K, a factor 10 higher than previously thought.
Pt-induced semimetallic transport and enhanced thermoelectric response in the half-Heusler alloy YNi_{0.5}Pt_{0.5}Bi
Indian Institute of Technology Delhi（印度德里理工学院）；Harbin Institute of Technology（哈尔滨工业大学）；Chalmers University of Technology（查尔姆斯理工大学）；Damanhour University（达曼胡尔大学）；Max-Planck-Institut für Chemische Physik fester Stoffe（马克斯·普朗克固体化学物理研究所）；Tohoku University（东北大学）
We analyze the thermal transport properties of the Falicov-Kimball model concentrating on locating regions of parameter space where the thermoelectric figure-of-merit ZT is large. We focus on high temperature for power generation applications and low temperature for cooling applications. We constrain the static particles (ions) to have a fixed concentration, and vary the conduction electron concentration as in the binary-alloy picture of the Falicov-Kimball model. We find a large region of parameter space with ZT>1 at high temperature and we find a small region of parameter space with ZT>1 at …
We report thermoelectric properties of Ir$_{1-x}$Rh$_x$Te$_2$ ($0 \leqslant x \leqslant 0.3$) alloy series where superconductivity at low temperatures emerges as the high-temperature structural transition ($T_s$) is suppressed. The isovalent ionic substitution of Rh into Ir has different effects on physical properties when compared to the anionic substitution of Se into Te, in which the structural transition is more stable with Se substitution. Rh substitution results in a slight reduction of lattice parameters and in an increase of number of carriers per unit cell. Weak-coupled BCS supercondu…
Thermoelectric transport and current noise through a multilevel Anderson impurity: Three-body Fermi-liquid corrections in quantum dots and magnetic alloys
