Synthesis of FeVSb1−xSex Half-Heusler Alloys via Mechanical Alloying and Evaluation of Transport and Thermoelectric Properties (original) (raw)
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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.
Thermoelectric Properties of Mn-Doped FeVSb Half-Heusler System Synthesized via Mechanical Alloying
Transactions on Electrical and Electronic Materials, 2018
Mn-doped FeVSb half-Heusler alloys were synthesized via a mechanical alloying process and consolidated by vacuum hot pressing. The microstructure and phase transformation of all the samples were examined by XRD and SEM. Thermoelectric properties such as the Seebeck coefficient, electrical conductivity and thermal conductivity were investigated in the moderate temperature range from 300 to 973 K. The negative value of both the Seebeck and Hall coefficients confirms the presence of n-type conductivity. The Seebeck coefficient increased with an increasing doping amount, but the electrical conductivity decreased, owing to decreasing carrier concentration. The thermal conductivity found in this experiment was quite high, possibly due to bipolar diffusion of the electronic band energy. The maximum value of the dimensionless figure of merit was achieved using a relatively high value of the Seebeck coefficient and a significantly higher value of electrical conductivity. The maximum value of ZT was observed for Fe 0.996 Mn 0.004 VSb at 468 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.
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.
Enhanced te performance of fevsb1-xsnx half-heusler matrices using zirconia vial
Journal of Ceramic Processing Research, 2020
Thermoelectric and transport properties of FeVSb1-xSnx (0.015<x<0.055) alloys were studied with respect to types of vials (zirconia and stainless steel), Sn contents and temperature. The results were compared with the previously studied samples synthesized by using stainless-vial. All the designated compositions in current work were prepared via a mechanical alloying process using a zirconia vial. Vacuum hot pressing was conducted to consolidate the mechanically alloyed powders. F43m symmetry was being confirmed from the Rietveld refinement pattern. The phase transitions during the milling process and vacuum hot processing were investigated and the results exhibited near single half-Heusler phases with a minor portion of the second phase within the matrix. The Second phase might play a role to reduce thermal conductivity. Electrical conductivity exhibited semi-metallic behavior in all the temperature range. Carrier concentrations are found to be decreased with the increasing Sn contents and the FeVSb0.955Sn0.045 specimen showed the ZT max of 0.23 at 757 K.
Journal of Physics D: Applied Physics, 2014
By using ab initio electronic structure calculations here we report the three new full Heusler alloys which are possessing very good thermoelectric behavior and expected to be synthesized in the laboratories. These are Fe2ScP, Fe2ScAs and Fe2ScSb compound. First two compounds are indirect band gap semiconductors and the last one shows semimetallic ground state. The value of band gap of Fe2ScP and Fe2ScAs is 0.3 and 0.09 eV, respectively. These compounds show the presence of flat conduction bands along Γ-X-direction suggesting for the large electron like effective mass and promising for very good thermoelectric behavior of the compounds. At 200 K, the Seebeck coefficients of Fe2ScP, Fe2ScAs and Fe2ScSb compounds are-770,-386 and-192µV/K, respectively. The maximum power factor (P F) is expected for the n-type doping in these materials. The heavily doped Fe2ScP and Fe2ScAs have P F >60 for a wide temperature range, which is comparable to the PF of Bi2Te3-a well known and one of the best commercially used thermoelectric material. Present work suggests the possible thermoelectric applicability of these materials in a wide temperature range.
Journal of Physics: Energy, 2021
Half-Heusler (HH) alloys are an important class of thermoelectric materials that combine promising performance with good engineering properties. This manuscript reports a variable temperature synchrotron x-ray diffraction study of several TiNiSn- and VFeSb-based HH alloys. A Debye model was found to capture the main trends in thermal expansion and atomic displacement parameters. The linear thermal expansion coefficient α(T) of the TiNiSn-based samples was found to be independent of alloying or presence of Cu interstitials with α av = 10.1 × 10−6 K−1 between 400 and 848 K. The α(T) of VFeSb and TiNiSn are well-matched, but NbFeSb has a reduced α av = 8.9 × 10−6 K−1, caused by a stiffer lattice structure. This is confirmed by analysis of the Debye temperatures, which indicate significantly larger bond force constants for all atomic sites in NbFeSb. This work also reveals substantial amounts of Fe interstitials in VFeSb, whilst these are absent for NbFeSb. The Fe interstitials are link...
Huge power factor in p-type half-Heusler alloys NbFeSb and TaFeSb
Journal of Physics: Materials, 2019
NbFeSb is a promising thermoelectric material which according to experimental and theoretical studies exhibits a high power factor of up to 10 mW m−1 K−2 at room temperature and ZT of 1 at 1000 K. In all previous theoretical studies, κ latt is calculated using simplified models, which ignore structural defects. In this work, we calculate κ latt by solving the Boltzmann transport equation and subsequently including the contributions of grain boundaries, point defects and electron–phonon interaction. The results for κ latt and ZT are in excellent agreement with experimental measurements. In addition, we investigate theoretically the thermoelectric properties of TaFeSb. The material has recently been synthesised experimentally, thus confirming the theoretical hypothesis for its stability. This encourages a full-scale computation of its thermoelectric performance. Our results show that TaFeSb is indeed an excellent thermoelectric material which has a very high power factor of 16 mW m−1 ...