Thermoelectric Properties of MnSi1.74-1.75:Ge&lt;i&gt;m&lt;/i&gt; Prepared by Solid-State Reaction and Hot Pressing

Half-Heusler (HH) thermoelectric materials are promising for mid- to high-temperature applications, and MNiSn (M = Ti, Zr, Hf) is a representative n-type HH alloy. In general, the M sites are mixed with isoelectronic elements Ti, Zr, and Hf, to lower the lattice thermal conductivity, and the Sn sites are doped with Sb to adjust the electron concentration. However, Hf is a rare element in earth’s crust, and the volatility of Sb makes it difficult to maintain the initial Sb amount during material synthesis. In this study, as an alternative, Ta was added in the M sites along with the host elements Ti and Zr to produce Hf-free Zr0.6-xTi0.4TaxNiSn alloys (0 ≤ x ≤ 0.04), and the effects of Ta doping on the thermoelectric properties were analyzed. The electrical conductivity of Zr0.6-xTi0.4TaxNiSn increased with Ta content, and the electron concentration increased almost linearly, reaching 5.6 × 1020 cm -3 at x = 0.04. By adding Ta, the maximum power factor also increased by approximately 17% to 3.94 × 10-3 W m-1K-2 at x = 0.02. The lowest lattice thermal conductivity (κlat) was observed at x = 0.02, reaching approximately 1.9 W m-1K-1 at 723 K, but overall, a dramatic decrease in κlat was not observed with Ta doping in Zr0.6-xTi0.4TaxNiSn. This is probably due to the existing effect of Zr/Ti mixing at the M sites, which enhances phonon scattering. A maximum figure of merit (zT) of 0.91 was obtained in Zr0.58Ti0.4Ta0.02NiSn at 873 K, which is a high value for ZrNiSn-based Hf-free HH materials. In conclusion, Ta doping is a viable method to replace Sb doping in ZrNiSn-based HH alloys.

Section: 서 론unclassified

Thermoelectric Properties of Ta-doped Zr0.6-xTi0.4TaxNiSn n-type Half-Heusler Materials

Joo¹,

Son²,

Jang³

et al. 2022

“…With the increasing demand for sustainable energy and the rapid increase in the use of mobile devices, energy harvesting, which is the process of capturing/storing ambient energy (heat, light, vibration, etc.) and converting it into electrical energy, has received growing attention [1][2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Bytizite Cu3SbSe3: Solid-State Synthesis and Thermoelectric Performance

Lee¹,

Kim²

2023

Bytizite (Cu3SbSe3 ) has attracted interest as a promising thermoelectric material because of its ultralow thermal conductivity; however, there are few experimental studies. This study investigated the optimal processing conditions for the synthesis of Cu3SbSe3 using mechanical alloying (MA) and hot pressing (HP). The MA powder exhibited an orthorhombic Cu3SbSe3 phase, which remained even after HP. However, secondary phases of permingeatite (Cu3SbSe4) and berzelianite (Cu1.78Se) were also identified in the X-ray diffraction patterns. Thermal analysis revealed that the MA powder and HP compacts exhibited a large endothermic peak near 727 K, which corresponds to the melting point of Cu3SbSe3 . Dense compacts with a relative density higher than 99% were obtained at HP temperatures above 573 K. Microstructural and elemental analyses confirmed the presence of the secondary phase Cu3 SbSe4 in the matrix of Cu3SbSe3 . However, the Cu1.78Se phase could not be observed. All specimens exhibited an electrical conductivity of (0.66–1.06) × 10 3 Sm-1, a Seebeck coefficient of 324–376 µVK-1, and a power factor of 0.09–0.11 mWm-1K-2 at 623 K. The thermal conductivity was lower than 0.7 Wm-1K-1 in the measured temperature range, mainly due to the phonon scattering caused by the lone-pair electrons of Sb. A dip in thermal conductivity was observed at 423 K, which was possibly caused by the order-disorder transition of bytizite. The dimensionless figure of merit ZT increased with increasing temperature, and the maximum ZT was 0.16 at 623 K.

“…The recent interest in ecofriendly power sources is inspiring research on waste heat recovery via thermoelectric generation. Among the promising thermoelectric materials for mid-to-high temperature applications, including skutterudites [1][2][3] and silicides [4][5][6], half-Heusler (HH) materials have attracted considerable attention because they show major advantages, such as high performance, mechanical robustness, and thermal stability [7][8][9]. NbFeSbbased HH compounds have recently been intensively investigated, and improved thermoelectric performances (TEPs) have been observed in the materials doped with Ti [10][11][12] and Hf [13,14].…”

Section: Introductionmentioning

confidence: 99%

Effects of V Alloying on Thermoelectric Properties of NbFeSb Half-Heusler Materials Codoped with Ti, Zr, and Sn

Joo¹,

Jang²,

Son³

et al. 2022

NbFeSb-based alloys are promising p-type half-Heusler materials with excellent thermoelectric performance, thermal stability, and naturally abundant constituent elements. Alloying and doping are powerful techniques for enhancing the thermoelectric properties of half-Heusler materials. This study experimentally investigated the effects of V alloying in NbFeSb codoped with Ti, Zr, and Sn. As the V content increases, the electrical conductivity of Nb0.8−xVxTi0.15Zr0.05FeSb0.98Sn0.02 (x = 0, 0.05, 0.1, 0.2, and 0.3) decreases monotonically because of a simultaneous reduction in carrier concentration and mobility, reducing the power factor up to −39% from 4.13 (x = 0) to 2.52 mW m−1K−2 (x = 0.3) at 298 K. Moreover, the lattice thermal conductivity decreases with increasing x by as much as −40% at the maximum V content of x = 0.3, demonstrating that V addition considerably enhances phonon scattering even in the presence of substitutional dopants Ti, Zr, and Sn. The differences in the mass and size of V and Nb atoms cause a substantial decrease in lattice thermal conductivity. According to our study, the addition of a small V content to Hf-free NbFeSbbased alloys can improve their thermoelectric properties, and a maximum dimensionless figure of merit zT of 0.89 was obtained in Nb0.75V0.05Ti0.15Zr0.05Sn0.98Sb0.02 at 973 K.