Thermoelectric Material For High Temperature Applications Research Articles

Insight into phase stability and thermoelectric properties of semiconducting iron silicides with manganese substitution: β-Fe1−xMnxSi2 (0≤x≤0.05)

Metal-doped iron silicides (β-FeSi2) are promising thermoelectric materials for high-temperature applications. However, the addition of metal dopants usually causes the formation of secondary metallic phases, resulting in the degradation of thermopower. Here we report the stability of semiconducting β-phase (higher than 95 %) of Mn-doped β-FeSi2 obtained at Mn concentration from 1 % to 5 %, where the samples were prepared through direct arc melting and heat treatment process. The carrier density remarkably increases with Mn content, but the mobility decreases. The electrical resistivity significantly decreases with Mn content. The Seebeck coefficient of Mn-doped samples is improved and stable at high-temperature regions because of the reduction of the bipolar effect and β-phase stability. The thermal conductivity slightly increases with Mn. As a result, the maximum thermoelectric power factor PF = 970 μWm−1K−2 and dimensionless figure of merit ZT = 0.12 at 800 K are obtained in a 3 % Mn-doped sample. The stability of β-phase and the improved carrier density are the origins of enhanced thermoelectric properties, where the Seebeck coefficient is improved, and the electrical resistivity is reduced. Our study provides insight into the importance of phase stability for enhancing thermoelectric transport in Mn-doped β-FeSi2.

Cyclic oxidation behaviour of N-type (Zr,Ti)Ni(Sn,Sb) and P-type (Zr,Ti)Co(Sn,Sb) thermoelectric materials

In this study, the fabricated Hf-free N-type (Zr,Ti)Ni(Sn,Sb) and P-type (Zr,Ti)Co(Sn,Sb) thermoelectric materials were subjected to cyclic oxidation testing at 500 °C for 10, 30, and 50 cycles. The oxidation behaviour of the materials was systematically investigated by evaluating mass gain to study the oxidation kinetics and by analysing surface morphology, phase constitution and elemental distribution to investigate the oxidation mechanism. The results indicated that both of the materials were severely oxidised during the cyclic oxidation testing, and the mass gain followed the parabolic kinetics and the parabolic rate constant (kp) being 0.006165 mg2cm−4s−1 and 0.000109 mg2cm−4s−1 for the N-type and the P-type TE materials, respectively. Alternated multilayers of Ni3Sn4+SnO2+(Zr,Ti)O2 and CoSb + SnO2+Sb2O4+(Zr,Ti)O2 were identified on the surface of the N-type and P-type materials, respectively, after the cyclic testing, which would deteriorate the thermoelectric performance of the materials. The outcome of this study strongly suggests that it is essential to improve the oxidation resistance and the thermal stability of the N-type (Zr,Ti)Ni(Sn,Sb) and P-type (Zr,Ti)Co(Sn,Sb) thermoelectric materials for high-temperature applications.

Role of atypical temperature-responsive lattice thermal transport on the thermoelectric properties of antiperovskites Mg3XN (X = P, As, Sb, Bi)

Antiperovskite materials have garnered significant attention due to their rich array of physical properties. In this study, we undertake a theoretical exploration into the phase stabilities, and the thermal and electronic transport properties of magnesium-based antiperovskite Mg3XN (X = P, As, Sb, and Bi) based on density functional theory (DFT) calculations, aiming at designing promising thermoelectric materials. The Mg3PN and Mg3AsN possess potential lattice distortion and strong quartic anharmonicity associated with the tilting displacement of Mg6N octahedra. After phonon renormalization, the thermal conductivity of Mg3PN and Mg3AsN exhibits relatively subdued temperature responsiveness with T−0.47 and T−0.62, respectively. Of note, the thermal conductivity of Mg3BiN drops the lowest at 900 K because of its distinctive rattle-dominated flat vibrational modes and strong temperature responsiveness with T−0.96, despite having a high initial value. Moreover, the combination of multiple degeneracy pockets and lighter dispersion band edges in Mg3XN ensures high Seebeck coefficient and impressive electronic conductivity, respectively. Ultimately, Mg3BiN achieves the optimal power factor, which also guarantees its excellent thermoelectric performance with the ZT values of 1.03 and 1.01 for n-type and p-type at 900 K, respectively. Our findings shed light on the significant impact of unconventional temperature-responsive lattice thermal conductivity on thermoelectric materials for high-temperature applications.

Effects of isotropic strain on the structure and transport properties of half-Heusler alloy BiBaK: a first-principles investigation.

In this study, using density functional and Boltzmann transport theories, we systematically investigated the effects of tensile and compressive strains on the elastic properties, phonon dispersion relation, electronic structure, and transport properties of the half-Heusler compound BiBaK. We calculated the elastic constants and phonon dispersion curves for BiBaK, which demonstrated its mechanical and thermodynamic stability, respectively, under different isotropic strains. Further, calculations showed that the electronic structure and energy bandgap of BiBaK changed with the application of isotropic strain. A high power factor and low thermal conductivity are key to improving the performance of thermoelectric materials. The figure of merit of BiBaK is 0.6 when it is unstrained and reaches a maximum value of 0.93 at -9% compressive strain and a temperature of 1200 K, indicating that under isotropic compressive strain, BiBaK compounds are efficient thermoelectric materials for high-temperature applications.

Microstructure and thermoelectric properties of pristine and Al-doped ZnO ceramics fabricated by cost-effective and eco-friendly wet chemistry methods

ZnO has potential as a thermoelectric material for high-temperature applications, but its performance is limited by the strong interconnection between electrical and thermal transportation. In this study we proved that ZnO bulk samples produced from cost-effective and environmentally friendly nitrates via ultrasonic spray pyrolysis and modified chemical precipitation methods followed by spark plasma sintering, demonstrate significantly higher thermoelectric performance than those fabricated from commercially available ZnO powder. To further explore the potential of the developed chemical precipitation technique, we synthesized a series of Al-doped samples with a nominal composition of Zn1–xAlxO (x = 0.02, 0.04, 0.06). The substitutuion of Al into the ZnO structure led to two significant effects: (i) a partial substitution of Zn with Al boosts the power factor; (ii) the formation of the ZnAl2O4 spinel phase acting as scattering center for phonons in addition to the mass and strain fluctuations induced by the partial Zn-Al substitution, both leading to the thermal conductivity reduction. As a result, Al doping led to a threefold enhancement of the thermoelectric performance with zT value of ∼0.12 achieved at 1100 K for the Zn0.94Al0.06O sample.

Novel metal oxides with promising high-temperature thermoelectric performance

By performing high-throughput calculations, we have successfully screened out a novel class of metal oxides MTa2O6 (M = Mg, Ca) as promising candidate thermoelectric materials for high-temperature applications.

Computational prediction of the thermoelectric performance of LaZnOPn (Pn = P, As)

State-of-the-art density functional theory is used to demonstrate that LaZnOP and LaZnOAs have great potential as earth-abundant p-type thermoelectric materials for high-temperature applications.

TiO2-SrTiO3 Biphase Nanoceramics as Advanced Thermoelectric Materials.

The review embraces a number of research papers concerning the fabrication of oxide thermoelectric systems, with TiO2−SrTiO3 biphase ceramics being emphasized. The ceramics is particularly known for a two-dimensional electron gas (2DEG) forming spontaneously on the TiO2/SrTiO3 heterointerface (modulation doping), unlike ordinary 2DEG occurrence on specially fabricated thin film. Such effect is provided by the SrTiO3 conduction band edge being 0.40 and 0.20 eV higher than that for anatase and rutile TiO2, respectively. That is why, in the case of a checkered arrangement of TiO2 and SrTiO3 grains, the united 2D net is probably formed along the grain boundaries with 2DEG occurring there. To reach such conditions, there should be applied novelties in the field of ceramics materials science, because it is important to obtain highly dense material preserving small (nanoscale) grain size and thin interface boundary. The review also discusses some aspects of reactive spark plasma sintering as a promising method of preparing perovskite-oxide TiO2−SrTiO3 thermoelectric materials for high-temperature applications.

High temperature thermoelectric properties of laser sintered thin films of phosphorous-doped silicon-germanium nanoparticles

Silicon-germanium (SiGe) is an important thermoelectric material for high-temperature applications. In this study, we show that the Seebeck coefficient of the laser sintered thin films of phosphorous (P)-doped Si80Ge20 nanoparticles increases from -144.9 μV/K at room temperature to -390.1 μV/K at 873 K. The electrical conductivity increases from 16.1 S/cm at room temperature to 62.1 S/cm at 873 K and demonstrates an opposite trend when compared to bulk nanostructured materials. The thermal conductivity from room temperature to 573 K is essentially constant within the measurement error of our system at ∼1.35 W/m⋅K. Therefore, if the thermal conductivity follows a similar temperature dependent trend as reported in past scientific literature, the figure of merit of the thin film Si80Ge20 is estimated to be 0.60 at 873 K which is comparable to a value of ∼1 for bulk nanostructured materials. This result indicates that thin film P-doped SiGe can provide comparable performance with bulk nanostructured SiGe materials by using nanoparticle laser sintering as an easier, quicker, and more cost-effective processing method.

Defect engineering for a markedly increased electrical conductivity and power factor in doped ZnO ceramic

ZnO is a promising thermoelectric material for high-temperature applications; however, the strong correlation between the electrical and thermal transport properties has limited their simultaneous optimization to achieve superior thermoelectric performance. In this work, defect engineering was applied to solve this problem. The results revealed that by eliminating the intrinsic acceptor defects at the grain boundaries, the Schottky barrier disappeared, which led to a huge increase in the Hall mobility. Meanwhile, an increased solid solution of the trivalent dopant Al was achieved to increase the carrier concentration. The increased Hall mobility and carrier concentration gave rise to a maximum electrical conductivity (σ310K) of 1.9 × 105 S m−1, showing a metallic-like behavior. Owing to the ultrahigh σ with moderate Seebeck coefficient, a maximum power factor of 8.2 × 10−4 W m−1 K−2 was obtained at 980 K. Moreover, by introducing large numbers of lattice defects in the grains, the lattice thermal conductivity was simultaneously decreased. Therefore, the multiple-doped ZnO ceramic with defect engineering of both grains and grain boundaries optimized the electrical and thermal transport properties in a relatively independent way which provided a new and effective route to optimize the performance of the ZnO-based thermoelectric materials.

共析Siと酸化鉄の酸化還元反応焼結によるβ-FeSi<sub>2</sub>基コンポジット熱電材料の創製

β-FeSi2 is an ecofriendly thermoelectric material for high-temperature applications. In the present work, we demonstrate the validity of a new proposed fabrication process for composite-type thermoelectric alloys comprising a β-FeSi2 matrix and dispersed SiO2 particles (including Fe2SiO4 particles). The starting materials were single-phase α-FeSi2 alloy powder and Fe2O3 powder. We propose that the following reaction sequence occurs during the sintering process: (1) α-FeSi2 decomposes into β-FeSi2 and Si via the eutectoid reaction, (2) SiO2 is formed by the oxidation of Si, and (3) β-FeSi2 is additionally formed by the solid-phase reaction between eutectoid Si and reduced Fe that is formed by the reduction of Fe2O3. The microstructure of the composite alloys formed by the combined reactions during the sintering process was observed and characterized mainly using scanning transmission electron microscopy in conjunction with energy-dispersive X-ray spectroscopic chemical analyses and X-ray diffraction. The electrical and thermoelectric properties of the composite alloys were measured at temperatures from 300 to 1073 K. High Seebeck coefficient values were observed for n-type Co-doped composite alloys from −150 to −250 μV•K−1 and for p-type Mn-doped alloys from 200 to 500 μV•K−1. The partitioning of the Co and Mn dopants from the α-FeSi2 phase to the β-FeSi2 phase throughout the process is important for controlling the Seebeck coefficient. The electrical resistivity is lowered by the dispersed SiO2 particles that are expected to reduce the lattice thermal conductivity of the composite alloys.

Thermoelectric Properties of High-Doped Silicon from Room Temperature to 900 K

Silicon is investigated as a low-cost, Earth-abundant thermoelectric material for high-temperature applications up to 900 K. For the calculation of module design the Seebeck coefficient and the electrical as well as thermal properties of silicon in the high-temperature range are of great importance. In this study, we evaluate the thermoelectric properties of low-, medium-, and high-doped silicon from room temperature to 900 K. In so doing, the Seebeck coefficient, the electrical and thermal conductivities, as well as the resulting figure of merit ZT of silicon are determined.

Chalcopyrite CuGaTe2: A High‐Efficiency Bulk Thermoelectric Material

CuGaTe(2) with a chalcopyrite structure demonstrates promising thermoelectric properties. The maximum figure of merit ZT is 1.4 at 950 K. CuGaTe(2) and related chalcopyrites are a new class of high-efficiency bulk thermoelectric material for high-temperature applications.