High-temperature Thermoelectric Devices Research Articles

Lone-pair electron-induced low lattice thermal conductivity and excellent thermoelectric performance of AuX (X = S, Se, Te) monolayers

We present a detailed study on the phonon thermal transport and thermoelectric (TE) properties of gold monochalcogenide AuX (X = S, Se, Te) monolayers via first-principles calculations and the Boltzmann transport theory. At room temperature, the calculated lattice thermal conductivity (κl) values in the x-direction (y-direction) were determined to be 12.66 (3.59), 6.06 (1.23), and 3.02 (0.40) W/(m·K) for the AuS, AuSe, and AuTe monolayers, respectively. The analysis of scattering matrix elements and anharmonic scattering rates suggested that the presence of strong bond anharmonicity leads to low κl values. This anharmonicity was induced by the nonlinear electrostatic repulsive force between lone-pair electrons (LPEs) surrounding the chalcogen atom and adjacent bonding electron. Furthermore, the AuS monolayer exhibited the highest bond anharmonicity among the three monolayers. This can be attributed to the reduced strength of the electrostatic repulsive force when electronegativity decreased from S to Se and Te. Although the AuS monolayer exhibited the strongest bond anharmonicity, its κl was still the largest, demonstrating that among the factors that influence κl, harmonic factors have a greater effect than anharmonic parameters. When the atomic mass was increased, the phonon frequencies, phonon group velocities, and κl decreased. Benefiting from low κl induced by LPEs, the maximum ZT values of p-type doped AuSe and AuTe monolayers exceeded 1.0 and 2.0 at T = 800 K, respectively. These results not only confirmed that the introduction of LPEs can reduce the lattice thermal conductivity and enhance the TE performance of 2D materials, but also demonstrated the promising potential of the 2D AuX family for applications in high-temperature TE devices.

A systemic study on Thallium based 3D halide perovskite with enhanced figure of merit

First principles calculations are carried out to explore structural, elastic, electronic, charge density and thermoelectric properties of TlZnX3 (X = F, Cl, Br and I) 3D halide cubic perovskites within the Generalized Gradient Approximation (GGA) through Quantum Espresso code. The elastic coefficients (C11, C12 and C44) and elastic modulii such as Young’s modulus, bulk modulus, shear modulus reveals that stiffness is higher in TlZnF3. Additionally using Pugh’s ratio and Cauchy’s pressure TlZnF3 is classified as ductile whereas TlZnX3 (X = Cl, Br and I) are classified as brittle materials. Phonon dispersion curve proves the dynamic stability of TlZnF3. The band structures of TlZnX3 (X = F, Cl and Br) and TlZnI3 shows semiconducting and metallic nature respectively. Due to replacement of halide ion the indirect band gap of TlZnX3 (X = F, Cl and Br) decreases from 3.82 eV, 1.39 eV and 0.37 eV as the size of the anion increases. Using the Boltztrap code, thermoelectric parameters are analysed at temperatures of 400 K, 600 K and 800 K and chemical potential provides insight about optimal dopant. Large Seebeck Coefficient combined with ultra low thermal conductivity results in a high figure of merit for TlZnF3 that satisfies industry standards (ZT ≈ 1). Together, these outcomes highlights that these Thallium based halide perovskite are reliable materials for high temperature thermoelectric devices.

Interfacial reaction and thermoelectric properties of Sr0.9La0.1TiO3 ceramic diffusion bonding joints with different electrode layers

n-Sr0.9La0.1TiO3 ceramic and Al2O3 substrate were welded by vacuum diffusion bonding with different electrode layers. Some intermetallic compounds could be observed at the interface when silver foil and nickel foil were applied as electrode layers. There was no obvious reaction product at the interface of joints when copper foil was employed as electrode layer. The joints fabricated using copper electrode layer showed the highest shear strength of 10.23 MPa. Furthermore, the thermoelectric properties of Sr0.9La0.1TiO3-20 wt %Ti/Cu joint were not significantly lower than that of intrinsic Sr0.9La0.1TiO3-20 wt %Ti thermoelectric material. In particular, the power factor value of Sr0.9La0.1TiO3-20 wt %Ti/Cu joint could reach 0.77 mW m−1 K−2 at 515 °C, which was 1.06 times that of intrinsic Sr0.9La0.1TiO3-20 wt %Ti thermoelectric material. After being aged in a vacuum environment at 675 °C for 15 days, the contact resistance of the SLT/Cu joint increased from 4.68 μΩ cm2 to 10.12 μΩ cm2, while the shear strength decreased from 10.23 MPa to 8.01 MPa. These results suggest that the interfacial properties, as characterized by contact resistance and shear strength, remained relatively stable and did not weaken significantly. The joints with copper electrode layer can meet the requirements of high-temperature application, which is beneficial to the production of high-temperature thermoelectric devices.

Properties of the double half-heusler alloy ScNbNi2Sn2 with respect to structural, electronic, optical, and thermoelectric aspects

In the current work, the structural, electronic, thermoelectrics, and optical characteristics of the double half Heusler (DHH) ScNbNi2Sn2 compound are reported for the first time using density functional theory (DFT). The computed band structures show typical semiconductor behavior with an indirect bandgap (0.47 eV) using EV-GGA approximation. We also investigated the optical properties such as the dielectric function, optical conductivity, refractive index. Boltzmann's semiclassical theory attempts to explain a simulation concept in the BoltzTrap software, and the findings were presented and analyzed in terms of electrical conductivity, electronic and lattice thermal conductivities, the Seebeck coefficient, and the Figure of merit over a 50 K–1000 K temperature range. At room temperature, with a low magnitude of lattice thermal conductivity (κL) (5.30776 W/m. K) and a maximum value of the merit factor (ZT) is 0.64 at 900 K for ScNbNi2Sn2 compound is observed. These findings suggest that our material may be a viable option for use in high-temperature thermoelectric devices. We calculated (S, (σ/τ), (ke/τ)) along the x, y, and z axes utilizing the EV-GGA method. We found out that our compound is thermoelectrically anisotropic. We have also studied in EV-GGA the effect of the carrier concentration on the Seebeck coefficnet at T = 600 K. The maximum value of S is 356.9905 μV/K with n=3.04×1019Cm−3 within GGA and EV-GGA respectively.

Theoretical determination of superior high-temperature thermoelectricity in an n-type doped 2H-ZrI2 monolayer.

Two-dimensional materials with a competitive figure of merit zT are extremely desirable for the fabrication of thermoelectric modules. In the present work, we systematically evaluated the thermoelectricity of monolayer 2H-ZrI2 through first-principles calculations and semiclassical Boltzmann transport theory. Apart from its all-round structural stability and feasibility of experimental preparation, the semiconducting material with a moderate indirect bandgap of 1.07 eV at the HSE06 level exhibits an acceptable lattice thermal conductivity κL of 6.69 W m-1 K-1 at 900 K contributed dominantly by acoustic modes. The four-phonon scattering is found to exert a minor effect on the κL of the monolayer. Moreover, a quite large power factor of up to 147.89 mW m-1 K-2 can be achieved due to the conduction band valley degeneracy near the Fermi level. These transport coefficients eventually give rise to a significant optimal n-type zT value as high as 3.57 at 900 K at a certain experimentally achievable electron doping concentration. Our study demonstrates the potential application of monolayer 2H-ZrI2 in high-temperature thermoelectric devices.

Electron-phonon coupling, bipolar effects, and thermoelectric performance of the CuSbS2 monolayer.

The thermoelectric performance of the CuSbS2 monolayer is determined using the relaxation times obtained from electron-phonon coupling calculations and the transport properties of phonons and electrons. Based on the fully relaxed structure, the lattice thermal conductivity and the electronic transport coefficients are evaluated by solving the Boltzmann transport equation for phonons and electrons under relaxation time approximation, respectively. The tendencies of the transport coefficients depending on the carrier concentrations and temperatures are studied to understand the thermoelectric performance. Based on the bipolar effect, the transport coefficients and intrinsic carrier concentrations, we determined the dimensionless figure of merit ZT in the 300-800 K range. The results demonstrate that the CuSbS2 monolayer should be an p-type semiconductor, and the maximum ZT of 1.36 is obtained, indicating that the monolayer is a good candidate for high-temperature thermoelectric devices. Substantial bipolar effects are observed, and the ones in the x-direction are stronger in comparison to those in the y-direction, which is responsible for the smaller ZT in the x-direction.

Scrutinized the inherent spin half-metallicity and thermoelectric response of f-electron-based RbMO3 (M = Np, Pu) perovskites: a computational assessment

In the hunt for novel materials, we present self-consistent ab initio simulations of the structural stability, electronic profile, and transport properties of f-electron-based RbMO3 (M = Np, Pu) perovskites within the context of density functional theory. The structural stability and thermodynamic concerns are fixed by relaxing the crystal structure and computing the energy of formation, respectively. Furthermore, the decisive physical features of given materials have been outlined using the optimised lattice constant retrieved from structural optimizations. The ground state magnetic phase stability is ascertained by minimizing Birch Murnaghan's equation of state in distinct magnetic phases, upholding the ferromagnetic phase (FM) as the ground state magnetic phase, which is further backed by positive Curie Wiess constant values. To specify the electronic structure, a mix of the two approximations GGA and GGA + mBJ has been executed, both of which assert the half-metallic character, culminating in 100% spin polarisation at the Fermi level. The study of the magnetic moment and Curie temperature of each material has further been assessed in the present study. Apart from half-metallicity, the thermoelectric response of the present materials is quantified by exploring the chemical potential dependency of several transport parameters like Seebeck coefficient, electrical and thermal conductivity, power factor, etc. Moreover, the thermoelectric competence has been tested using a zT calculation, adapting values of 1.01 and 0.987 at 300 K for RbNpO3 and RbPuO3, respectively. The high electronic zT at encompassing temperatures uncovers the significant utility of these materials in both low-and high-temperature thermoelectric device applications. In essence, the comprehensive survey of these alloys could certainly open up their possibilities in spintronics, thermoelectric, and solid-state (RTG) device applications.

First-principles study of anti-perovskites Ca4Pn2O (Pn = As, Sb, Bi) as a potential optical material

Anti-perovskite materials have potential applications in solid-state batteries, high-temperature thermoelectric devices and optical devices. In the current work, through the first principle calculations, we find that Anti-perovskites Ca4Pn2O (Pn = As, Sb, and Bi) have the gradually decreased band gaps of 2.078, 1.885 and 1.688 eV (HSE06 method), respectively due to the gradually increased covalent components of Ca–O and Ca-Pn (As, Sb, Bi) bonds with the increasing atomic numbers of As, Sb and Bi. The effective carrier masses of Ca4Pn2O (Pn = As, Sb, Bi) intrinsic semiconductors are small, and decrease in the principal directions. The large absorption coefficients and small effective carrier masses promise Ca4Pn2O (Pn = As, Sb, Bi), especially Ca4Bi2O, to be p-type visible light-absorbing semiconductor materials. The Raman spectra of Ca4Pn2O (Pn = As, Sb, and Bi) contain the double degenerate mode Eg and single mode A1g while the infrared spectra contain the double degenerate mode Eu and single modes A2u and B1u. This work provides valuable information for future research on Ca4Pn2O (Pn = As, Sb, Bi) anti-perovskites.

Structure induced modification on thermoelectric and optical properties by Mg doping in CuCrO2 nanocrystals

P-type semiconductors draw special attention because of its application in high-temperature thermoelectric devices and sensors. Oxide materials showing a negative temperature coefficient of resistance at high-temperatures make them good substitutes as one leg of the devices. Proper doping makes CuCrO2 a potential P-type semiconductor for TE application. The study incorporate Mg2+ for Cr3+ site in delafossite CuCrO2 crystal lattice. High-temperature solid-state reaction route has been chosen for the synthesis CuCrMgO2, by taking appropriate proportion of Cu2O, Cr2O3, and MgO. The structural studies were done by XRD, Raman analysis, FTIR, and SEM. CuCrMgO2 pellets with a thickness of 2 mm and a diameter of 13 mm were prepared for thermoelectric studies. By varying doping percentages, considerable changes in conductivity were observed. The highest conductivity of 1149.42 S/m was obtained for 1.5 wt% sample at 600 °C. It was observed that the electrical conductivity increased with the increase of doping percentages while the Seebeck coefficient decreased, which led to a maximum increase of 1.95 times in the power factor of CuCrO2. The maximum power factor of 1.2153 × 10−4 W/mK2 was calculated for 0.5 wt% doped sample at 600 °C. The electronic spectroscopic studies at ambient conditions reveal weak absorbance in the wavelength range of 300–400 nm for all samples. It is also found that increased absorbance, and direct optical band gap variation between 3.35 and 3.44 eV with doping.

The effects of Ba0.85Ca0.15Zr0.1Ti0.9O3 addition on the phase, microstructure, and thermoelectric properties of Ca3Co4O9 ceramics

ABSTRACT In this work, the influences of Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) addition on phase, microstructure, and thermoelectric properties of Ca3Co4O9 (CCO) were investigated. (1-x)CCO-(x)BCZT ceramics where x= 0, 0.003, 0.005, and 0.010 were fabricated successfully via a conventional solid-state sintering at 1,223 K for 24 h. The substitution of BCZT introduced the chemical defects (, , ) in CCO ceramic, which increased charge carrier concentration and enhanced the electrical conductivity. The presence of Ca3Co2O6 phase and Co3+ improved the Seebeck coefficients of CCO ceramic. The thermal conductivity of CCO ceramic decreased when BCZT was added. The addition of BCZT at x = 0.010 promoted the highest thermoelectric power factor (PF~235 μW/mK2), and the highest figure of merit (ZT~0.5) at 800 K, which presents this ceramic an alternative p-type oxide thermoelectric for a high-temperature thermoelectric device.

Half-metallic and thermoelectric properties of Sr2EuReO6

Structural parameters, electronic band structure, half-metallic and thermoelectric properties of Sr2EuReO6 compound materials are investigated. The computations are performed using density-functional calculations within the generalized gradient approximation. Electronic results show half-metallic nature with majority spin channels as metallic and minority spin channels as semi-conducting. Magnetic moment calculated within GGA + U was found equal to 8.00 μB. The half metallicity is attributed by the double-exchange interaction mechanism via the Re(5d)–O(2p)–Eu(4f) hybridization. Boltzmann theory is employed to check the thermoelectric response, where Seebeck coefficient of 297.97 μVK−1, electrical conductivity of 44.96 × 1019 Ω−1m−1s−1 and lattice thermal conductivity of 5.94 × 1015 W/mK−1s−1 is seen. The thermoelectric efficiency measured through ZT calculation with a value of 1 at 300 K, indicating that Sr2EuReO6 can work at low as well as high temperature thermoelectric devices operations. Based on our calculations, Sr2EuReO6 combine both good spintronic and thermoelectric behaviors that may be used in spin injection applications.

Atomistic structure and three-dimensional spatial distribution of oxide clusters along voids in nitride metal/semiconductor superlattices

Epitaxial metal/semiconductor superlattices with atomically sharp interfaces and tunable Schottky barrier heights have attracted significant interest in recent years for thermionic emission-based high-temperature thermoelectric devices, optical hyperbolic metamaterials, hot-electron photocatalysis, and optoelectronic heterostructures for visible-to-terahertz frequency range applications. ZrN/ScN is a demonstration of such epitaxial metal/semiconductor superlattices and exhibits atomically sharp lattice-matched interfaces, albeit with the presence of threading dislocations on MgO substrates. Along with its influence on structural integrity and atomic diffusion, the presence of such defects significantly impacts electron and phonon transport in these metamaterials with carrier trapping, scattering, shunt path, etc. Therefore, an in-depth analysis of the atomistic structure and the composition of such defects is extremely necessary to design devices with improved efficiencies. In this paper, high-resolution scanning transmission electron microscopy and atom-probe tomography are employed to determine the structure and three-dimensional (3D) spatial distribution of oxide defect clusters along the voids in ZrN/ScN superlattices. $\mathrm{Sc}{\mathrm{O}}^{+}$ and $\mathrm{Sc}{\mathrm{O}}^{++}$ ions are found to cluster predominantly along such 3D interface defects with zirconium and scandium atoms surrounding them. Defect regions are also found to be depleted of nitrogen atoms and rich with a high concentration of oxygen. The oxygen content was found to be higher inside the ScN layers compared to ZrN. First-principles modeling analysis verified the clustering of oxygen at high oxygen partial pressure and demonstrated a higher affinity of scandium towards oxygen than for zirconium towards oxygen. These results mark significant progress in understanding the atomic structure and composition of defects in nitride superlattices.

Half-metallic ferromagnetism and thermoelectric properties of vanadium doped Hf1−xVxO2 (x = 0, 0.25, 0.50, 0.75) alloys by first principles perspective

In this work, we have reported the first-principles calculations based on functional theory density on the structural, electronic, magnetic, bonding nature and thermoelectric properties of Hf1-xVxO2 alloys (x = 0, 0.25, 0.50, 0.75). For all the materials, the equilibrium structural parameters like that of lattice constant, bulk modulus and first pressure derivative of bulk modulus have been computed. The band profile and the density of states results demonstrate half-metallic nature for Hf1-xVxO2 alloys (x = 0.25, 0.50, 0.75). The calculated total magnetic moment was 1.0 μB/cell, 2.0 μB/cell, and 3.0 μB/cell, and the partial moment of V or local contribution is 1.08 μB, 1.85 μB, and 2.73 μB, respectively for Hf1-xVxO2 alloys (x = 0.25, 0.50, 0.75). The transport properties such as Seebeck coefficient, thermo power and thermal conductivity are found to have a great variation with V concentration. These alloys may find suitable applications in spintronic materials and in high temperature thermoelectric devices.

Optoelectronic and thermal properties of cubic SiMO3 (M = Sn, Pb) oxides for device application: a first principle study

Cubic perovskites have picked up a potential intrigued by the researchers for their wide-ranging applications within the field of optoelectronic and thermoelectric devices. The research work illustrated in this article mainly emphases on the theoretical study of silicon-based perovskites SiMO3 (M = Sn, Pb) for which density functional theory centered on the first principle technique within the full-potential linearized augmented plane wave method and generalized gradient approximation is utilized within the WIEN2k code. The examined materials are stable in the cubic phase, which is affirmed by its structural properties. The examined results reveal that SiSnO3 and SiPbO3 have indirect bandgap values 0.7 eV and 0.9 eV respectively and showing semiconducting behavior. Also, the optical parameters of the examined compounds have been investigated in expressions of dielectric functions, extinction coefficient, refractive index, reflectivity, absorption coefficient, and energy loss factor. Both materials are sensitive to ultraviolet light in the electromagnetic spectrum perceived by the optical properties. The transparency and maximum reflectivity to the definite energies and the proof of Penn’s model indicates that the compounds are more practicable for optical device applications. Lastly, the thermoelectric properties are estimated by elucidating the Boltzmann transport equation. The outcomes of thermal properties tell that SiSnO3 and SiPbO3 have ZT of 0.58 and 0.59, respectively. The p-type conductivity of the studied perovskite materials discloses on the basis of a positive Seebeck coefficient. Both compounds work at their best at 800 K, proposing high-temperature thermoelectric device applications.

A promising thermoelectric response of fully compensated ferrimagnetic spin gapless semiconducting Heusler alloy Zr2MnAl at high temperature: DFT study

In recent times, Heusler compounds have emerged as potential candidates for spintronics and thermoelectric materials owing to their interesting properties such as gapless semiconducting nature with fully compensated ferrimagnetic behavior, 100% spin polarization with high mobility of charge carriers and better thermoelectric figure of merit. Motivated by this fact, we have carried out a systematic theoretical investigation of structural, electronic, magnetic, thermoelectric and lattice dynamical properties of spin gapless Heusler alloy Zr2MnAl within the frame work of density functional theory based first principle calculation. Our ground state total energy calculations confirms the structural stability of antiferromagnetic phase of Zr2MnAl over ferromagnetic phase, which is in agreement with previous study. The positive value for Cauchy’s pressure (C12–C44) predicts ductile nature of the material. The band structure calculation reveals indirect band gap in spin down channel and zero band gap in spin up channel of valence and conduction bands confirming the spin gapless semiconducting nature of the compound. The real frequency of phonon modes throughout the Brillouin zone confirms the structural and dynamical stability of antiferromagnetic phase of Zr2MnAl, which is reported for the first time as per our knowledge. Calculated Seebeck coefficient in spin up and spin down channel reveals that the Zr2MnAl behaves as both n and p type thermoelectric materials with better output efficiency. The calculated thermoelectric figure of merit of 1.4 at 800 K, favors use of an alloy in recovery of waste heat at higher temperature and thermoelectric spin generators. The comprehensive analysis of various chemical potential dependent thermoelectric coefficients for enhancing thermoelectric performance for the material has been carried out. The obtained results propose Zr2MnAl as a potential candidate for high temperature thermoelectric devices. Higher optical gap in the phonon dispersive curve is responsible for decrease in lattice thermal conductivity with temperature, resulting in enhancement in thermoelectric figure of merit.

Structural, electronic, optical and thermoelectric investigations of antiperovskites A3SnO (A = Ca, Sr, Ba) using density functional theory

Density functional theory study of the structural, electrical, optical and thermoelectric behaviors of very less investigated anti-perovskites A3SnO (A = Ca, Sr, Ba) is performed with FP-LAPW technique. The A3SnO exhibit narrow direct band gap, in contrast to the wide indirect band gap of the respective perovskites. Hence, indirect to direct band gap transformation can be realized by the structural transition from perovskite to anti-perovskite. The p-p hybridization between A and O states result in the covalent bonding. The transparency and maximum reflectivity to the certain energies, and the verification of the Penn's model indicate potential optical device applications. Thermoelectric behaviors computed within 200–800 K depict that Ca3SnO exhibits good thermoelectric performance than Ba3SnO and Sr3SnO, and all three operate at their best at 800 K suggesting high temperature thermoelectric device applications.

Phonon wave effects in the thermal transport of epitaxial TiN/(Al,Sc)N metal/semiconductor superlattices

Epitaxial single crystalline TiN/(Al,Sc)N metal/semiconductor superlattice metamaterials have generated significant interest in recent years for their potential applications in high temperature thermoelectric devices, optical hyperbolic metamaterials in the visible and near infrared-spectral range, and as candidates for solar-thermophotovoltaics and high temperature electronic materials. While significant progress in their structural, mechanical, and optical properties has been made, in-depth analysis and detailed understanding of their thermal transport mechanism remain to be addressed. In this article, we show that in short-period epitaxial, lattice-matched TiN/(Al,Sc)N metal/semiconductor superlattices, thermal transport is dominated by phonon wave effects as the wavelengths of phonons that carry significant amounts of heat become comparable to the superlattice period thickness. Due to the increasing contribution of such phonon wave-modes, the cross-plane thermal conductivity at short-periods increases with decreasing period thicknesses resulting in a distinct minimum of thermal conductivity at a period thickness of about 4 nm at room temperature. Thermal conductivity of the superlattices also decreases with an increase in the temperatures due to Umklapp scattering, which supports the wave-nature of the phonon transport mechanism. These results show that the lattice-matched, epitaxial TiN/(Al,Sc)N metal/semiconductor superlattices behave as an effective medium with respect to phonon transport at short-periods, and the wave-nature of phonon dominates the heat conduction mechanism at such length scales.

Photocatalytic and thermoelectric properties of Cu2MnSnS4 nanoparticles synthesized via solvothermal method

Flower-like Cu2MnSnS4 nanoparticles were synthesized by the solvothermal method for the first time. X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM) show that pure Cu2MnSnS4 exhibit flower-like structure and the thickness of the petal is about 40nm. The degradation rate of methylene blue(MB) with under visible-light irradiation is about 85%, indicating a promising candidate for effective visible-light photocatalyst to treating the waste water treatment. The high electrical conductivity(σ) and large Seebeck coefficient(S) were obtained, the values are 33.75Sm−1 and 464.88μVK−1 at 675K, respectively. The novel thermoelectric properties of Cu2MnSnS4 might be useful for high-temperature thermoelectric devices using earth abundant materials.

Thermal Stability Study from Room Temperature to 1273 K (1000 °C) in Magnesium Silicide

Doped magnesium silicide has been identified as a promising and environmentally friendly advanced thermoelectric material in the temperature range between 500 K and 800 K (227 °C and 527 °C). Besides the plethora of magnesium silicide thermoelectric advantages, it is well known for its high sensitivity to oxidation. Oxidation is one of the primary instability mechanisms of degradation of high-temperature Mg2Si thermoelectric devices, as in the presence of O2, Mg2Si decomposes to form MgO and Si. In this work, commercial magnesium silicide in bulk form was used for thermal stability study from room temperature to 1273 K (1000 °C). Various techniques such as DTA-TG, PXRD, and FTIR have been applied. Moreover, the application of thermoluminescence (TL) as an effective and alternative probe for the study of oxidation and decomposition has been exploited. The latter provides qualitative but very helpful hints toward oxidation studies. The low-detection threshold of thermoluminescence, in conjunction with the chemical composition of the oxidation byproducts, consisting of MgO, Mg2SiO4, and SiO2, constitute two powerful motivations for further investigating its viable use as proxy for instability/decomposition studies of magnesium silicide. The partial oxidation reaction has been adopted due to the experimental fact that magnesium silicide is monitored throughout the heating temperature range of the present study. Finally, the role of silicon dioxide to the decomposition procedure, being in amorphous state and gradually crystallizing, has been highlighted for the first time in the literature. Mg2Si oxidation takes place in two steps, including a mild oxidation process with temperature threshold of 573 K (300 °C) and an abrupt one after 773 K (500 °C). Implications on the optimum operational temperature range for practical thermoelectric (TE) applications have also been briefly discussed.

Synthesis and characterization of Sr2TiMO6 (M = Fe,Co) double perovskites for high temperature thermoelectric applications

ABSTRACTThe prospects of double perovskites based materials as the candidate for high temperature thermoelectric materials were investigated. Among the various complex perovskites, SrTiO3 based oxides had shown great potential for thermoelectric applications. In the current investigation, Sr2TiMO6 (M = Fe, Co) based double perovskites were synthesized using conventional solid-state route. The oxide samples were then investigated for their crystal structure (single phase) and morphology by XRD and SEM, respectively. Thermopower or Seebeck coefficient (S) and electrical conductivity (σ) of these oxide samples were measured simultaneously in the temperature range from 300 K to 1125 K. Large thermopower was obtained for these oxides in the wide range of temperature. Furthermore, thermoelectric power factor (S²σ) of these oxides were calculated to explore their potential for use in the high temperature thermoelectric devices.