Thermoelectric Properties of Mn-Doped FeVSb Half-Heusler System Synthesized via Mechanical Alloying (original) (raw)
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Journal of Electronic Materials, 2019
Se-doped half-Heusler compositions, FeVSb 1Àx Se x (0.03 £ x £ 0.15), were fabricated by mechanical alloying followed by vacuum hot pressing. The goal of this synthesis was to explore the effect of Se doping on the thermoelectric and transport properties of FeVSb system. A near single half-Heusler phase was found to form; however, a second phase of FeSb 2 couldn't be avoided in this process. N-type conduction was confirmed and Se acted as a donor for the FeVSb system. Lattice thermal conductivity also considerably decreased after Se doping. The absolute value of Seebeck coefficient is increased to a maximum of 126 lVK À1 at 956 K for x = 0.12, which may help to increase the figure of merit (ZT) of the FeVSb system. The figure of merit is improved by Se doping, and the improvement is possibly owing to the combined effect of fine grain structure, increased effective mass and phonon scattering at the grain boundaries. A maximum ZT of 0.27 was achieved for FeVSb 0.88 Se 0.12 at 847 K.
Transactions on Electrical and Electronic Materials, 2018
In the current work, we tried to investigate and compare the thermoelectric performance of the FeVSb 1−x Sn x (x = 0.0-0.05) half-Heusler system. The elemental mixture was formulated and subjected to mechanical alloying, and subsequently consolidated using vacuum hot pressing. X-ray diffractometry analysis was used to observe phase transition during the process, and scanning electron microscopy was utilized for microstructure analysis. After vacuum hot pressing, a near single phase of FeVSb 1−x Sn x (x = 0.0-0.05) was observed with small portions of second phases. The vacuum hot-pressed samples were analyzed to study the thermoelectric properties as a function of temperature up to 980 K. The n-type conduction was confirmed from Seebeck and Hall coefficients in the test range. In addition, the electrical conductivity showed combined conduction behavior in the test range, while the thermal conductivities showed abnormal behavior. Mass fluctuation scattering and changing in carrier concentration might have taken place during doping. The Seebeck coefficient and electrical conductivity of the system also decreased after doping. Dimensionless figure of merit values were calculated and compared with the results of analogue studies. The maximum ZT value was obtained for x = 0.01 at 553 K.
Transport and thermoelectric properties of Hf-doped FeVSb half- Heusler alloys
Journal of Alloys and Compounds, 2020
Nearly single-phase FeVSb half-Heusler alloys with fine grains were obtained by induction melting followed by mechanical alloying (MA), spark plasma sintering (SPS) and annealing process. Hf as a heavy element was used as dopant to present point defects aiming at decreasing the material's thermal conductivity during phonon scattering. Thermoelectric properties of the FeV 1Àx Hf x Sb samples (0.0 x 0.3) were investigated as a function of temperature in a range from 300 to 600 K. Microstructure investigations showed that grain size decreases with increasing the level of Hf doping (x). Seebeck coefficient of the parent FeVSb compound showed negative sign which refers to n-type conduction. Interestingly, the sign has changed to positive with introducing Hf in the FeVSb lattice at different concentrations (x ! 0.1), which is due to one less valence electron in Hf as compared to V. The difference between the host atom (V) and the impurity atom (Hf) in terms of mass and size has resulted in a mass fluctuation and consequently a disorder scattering. The absolute value of the Seebeck coefficient |S| of the FeVSb system was measured at 110 mV/K, while the thermal conductivity value was obtained at 10.46 Wm À1 K À1 near room temperature. A maximum power factor of 1.07 mWm À1 K À2 at 420 K was recorded. The thermal conductivity decreased rapidly upon Hf doping due to increased point defect scattering caused by Hf introducing to the FeVSb system. A maximum ZT value of 0.08 at 573 K for FeV 0.9 Hf 0.1 Sb was recorded in this study.
Electronic Materials Letters, 2018
The thermoelectric and transport properties of Ti-doped FeVSb half-Heusler alloys were studied in this study. FeV 1−x Ti x Sb (0.1 < x < 0.5) half-Heusler alloys were synthesized by mechanical alloying process and subsequent vacuum hot pressing. After vacuum hot pressing, a near singe phase with a small fraction of second phase was obtained in this experiment. Investigation of microstructure revealed that both grain and particle sizes were decreased on doping which would influence on thermal conductivity. No foreign elements pick up from the vial was seen during milling process. Thermoelectric properties were investigated as a function of temperature and doping level. The absolute value of Seebeck coefficient showed transition from negative to positive with increasing doping concentrations (x ≥ 0.3). Electrical conductivity, Seebeck coefficient and power factor increased with the increasing amount of Ti contents. The lattice thermal conductivity decreased considerably, possibly due to the mass disorder and grain boundary scattering. All of these turned out to increase in power factor significantly. As a result, the thermoelectric figure of merit increased comprehensively with Ti doping for this experiment, resulting in maximum thermoelectric figure of merit for FeV 0.7 Ti 0.3 Sb at 658 K.
Optimizing the thermoelectric performance of FeVSb half-Heusler compound via Hf-Ti double doping
• Electrical conductivity was improved due to optimizing the carrier concentration. • A reduction in thermal conductivity was achieved due to point defect scattering. • Significant enhancement in thermoelectric figure of merit (zT) was achieved. • The highest zT value at T = 873 K was achieved for Fe(V 0.8 Hf 0.2) 0.8 Ti 0⋅2 Sb sample. • Lower thermal conductivity is attributed to the Hf-Ti dual-doping. A R T I C L E I N F O Keywords: Thermoelectric performance Half-heusler alloys Hf-Ti dual-doping Disorder scattering parameters Phonon scattering Lattice thermal conductivity A B S T R A C T FeVSb-based half-Heusler (HH) compound has recently been identified as promising medium-high temperature thermoelectric (TE) materials for power generation applications. In this study, enhanced thermoelectric performance of Fe(V 0.8 Hf 0.2) 1-x Ti x Sb (x = 0.0, 0.2, 0.4, 0.5, 0.6) HH alloys by Hf-Ti dual-doping was reported studied in a temperature range from 100 to 900 K. A high content of Ti doping not only optimized the carrier concentration but also reduced the lattice thermal conductivity, which all contribute to high zT. As a result, a zT value was increased by ~20% at 873 K for Fe(V 0.8 Hf 0.2) 0.8 Ti 0.2 Sb compound. Hf-Ti dual doping significantly reduced the lattice thermal conductivity due to enhanced point defect scattering which is mainly attributed to mass fluctuations. Hence, suppressed the material's total thermal conductivity. A reduction of ~20% was obtained for the Fe(V 0.8 Hf 0.2) 0.8 Ti 0.2 Sb sample, compared with the single Hf-doped FeVSb sample and of ~80% compared to FeVSb at room temperature.
Acta Materialia, 2017
A re-investigation of phase equilibria, crystal structure and homogeneity region of the Half-Heusler (HH) phase in the ternary system Nb-Fe-Sb at 600 °C has solved controversies in the literature confirming the version of Melnyk et al. ([1] J. Phase Equilibria 20(2) (1999) 113-118). For the first time transport properties of Half-Heusler (HH) compounds NbFeSb and Nb 0.85 M 0.15 FeSb (M = Ti, Zr, Hf) were studied in the full temperature range from 4.2 to 823 K. The semiconducting material NbFeSb has an electronic structure close to a metal-to-insulator transition, which leads to changes of the conductivity type with the composition as well as with increasing temperature. Ti, Zr and Hf doped NbFeSb alloys show metallic behavior and were confirmed to be high ZT p-type thermoelectric materials. Surprisingly, the lattice thermal conductivity for the Zr-doped composition was found to be higher than those of the Ti-and Hf doped materials; this effect can be explained in terms of mass and strain field fluctuations. For the first time we report experimental information on thermal expansion coefficients, specific heat and elastic moduli for these p-type compounds. The mechanical properties show a good compatibility with those previously reported for n-type HH alloys.
Introduction of resonant states and enhancement of thermoelectric properties in half-Heusler alloys
Physical Review B, 2011
The inclusion of small concentrations of vanadium (less than 1%) was found to produce a substantial increase in the Seebeck coefficient of polycrystalline n-type half-Heusler alloys based on Hf 0.75 Zr 0.25 NiSn. Some degree of vanadium-induced thermopower enhancement was found to be present even at temperatures as high as 800 K. Electrical resistivity values of the vanadiumdoped samples, on the other hand, exhibited only modest increases, thereby resulting in a 120% increase in the thermoelectric power factor of Hf 0.75 Zr 0.25 NiSn above room temperature. Such augmentation of the Seebeck coefficient, however, was diminished at all measured temperatures with the addition of a sufficient quantity of antimony to dope this class of compounds optimally. These observations are discussed in terms of carrier concentration, mobility, effective mass, and calculations of the effective gap size. When taken in conjunction with low temperature heat capacity measurements, these results indicate an increase in the density of states at the Fermi level that is consistent with the resonant state phenomena investigated earlier by theoretical work on semiconductors.
Thermoelectric properties of Fe2TiAl Heusler alloys
Journal of Alloys and Compounds, 2004
Electric properties D 8000 Thermoelectric Properties of Fe 2 TiAl Heusler Alloys.-The influence of partial substitution of Fe or Ti by Ni, Co, or Cr in Fe2TiAl on the thermoelectric properties is studied. In the Heusler single-phase region the Seebeck coefficient decreases when a fourth elements are introduced. The maximum and minimum Seebeck coefficients are 50 µV/K for Fe2(Ti0.6Cr0.4)Al and-34 µV/K for (Fe0.2Co0.8)2TiAl, respectively. The electric conductivities are metallic judged by their temperature dependency. The characteristic semiconducting behavior of the Fe2VAl Heusler alloy due to a pseudo gap in the density of state is not observed in the substituted Fe2TiAl alloys.-(SUZUKI*, R.
Development of Thermoelectric Half-Heusler Alloys over the Past 25 Years
Crystals
Half-Heusler alloys are among the most promising thermoelectric materials. In the present review, thermoelectric properties (at 300 K and 800 K) of more than 1100 compositions from more than 220 publications between 1998 and 2023 were collected and evaluated. The dependence of the peak figure of merit, ZTmax, of p- and n-type half-Heusler alloys on the publishing year and the peak temperature is displayed in several figures. Furthermore, plots of ZT vs. the electrical resistivity, the Seebeck coefficient and the thermal conductivity at 300 K and 800 K are shown and discussed. Especially thermal conductivity vs. power factor leads to a good overview of ZT. For both p- and n-type individually separated into systems, ZTs and peak ZTs in dependence on the composition are displayed and discussed. This overview can help to find the ideal half-Heusler alloy for practical use.
Conventional Half-Heusler Alloys Advance State-of-the-Art Thermoelectric Properties
arXiv (Cornell University), 2022
Half-Heusler phases have garnered much attention as thermally stable and non-toxic thermoelectric materials for power conversion in the mid-to-high temperature domain. The most studied half-Heusler alloys to date utilize the refractory metals Hf, Zr, and Ti as principal components. These alloys can quite often achieve a moderate dimensionless figure of merit, ZT, near 1. Recent studies have advanced the thermoelectric performance of half-Heusler alloys by employing nanostructures and novel compositions to achieve larger ZT, reaching as high as 1.5. Herein, we report that traditional alloying techniques applied to the conventional HfZr-based half-Heusler alloys can also lead to exceptional ZT. Specifically, we present the well-studied p-type Hf0.3Zr0.7CoSn0.3Sb0.7 alloys, previously reported to have a ZT near 0.8, resonantly doped with less than 1 atomic percent of metallic Al on the Sn/Sb site, touting a remarkable ZT near 1.5 at 980 K. This is achieved through a significant increase in power factor, by ~65%, and a notable but appreciably smaller decrease in thermal conductivity, by ~13%, at high temperatures. These favorable thermoelectric properties are discussed in terms of a local anomaly in the density of states near the Fermi energy designed to enhance the Seebeck coefficient, as revealed by firstprinciples calculations, as well as the emergence of a highly heterogeneous grain structure that can scatter phonons across different length scales, effectively suppressing the lattice thermal conductivity. Consequently, the effective mass is significantly enhanced from ~ 7 to 10me within a single parabolic band model, consistent with the result from first-principles calculations. The discovery of high ZT in a commonly studied half-Heusler alloy obtained through a conventional and non-complex approach opens a new path for further discoveries in similar types of alloys. Furthermore, it is reasonable to believe that the present study will reinvigorate effort in the exploration of high thermoelectric performance in conventional alloy systems.