Thermoelectric Response Research Articles

A theoretical investigation of the lead-free double perovskites halides Rb2 XCl6 (X = Se, Ti) for optoelectronic and thermoelectric applications.

In this study, structural, electronic, optical, thermoelectric, and thermodynamics properties of vacancy-ordered double perovskites Rb2 XCl6 (X = Se, Ti) were explored theoretically. The results revealed that Rb2SeCl6 and Rb2 TiCl6 are indirect band gap (Eg ) semiconductors with Eg values of 2.95 eV, and 2.84 eV respectively. The calculated properties (phonons, elastic constant, Poisson's ratio, and Pugh's ratio) revealed that both materials are dynamically and chemically stable and can exhibit brittle (Rb2 SeCl6 ) and ductile (Rb2 TiCl6 ) nature. From the analysis of optical parameters, it was noticed that the refractive index of the materials has a value of 1.5-2.0 where light absorption was found from the visible to the ultraviolet region. The thermoelectric properties determined by using the BoltzTrap code demonstrated that at room temperature, the Figure of merit (ZT) was found to be 0.74 and 0.76 for Rb2 SeCl6 and Rb2 TiCl6 , respectively. Despite a moderate value of ZT in such materials, further studies might explore effective methods for tuning the electronic band gap and improving the thermoelectric response of the material for practical energy production applications.

First-principles analysis of the physical properties of XAcTe2 (X = Li, Na) Heusler alloys for optoelectronic and thermoelectric devices

Materials with diverse properties are in high demand due to their utilization in multipurpose devices. The current work presents the systematical analysis of electronic structure, mechanical, optoelectronic and transport properties of new Heusler XAcTe2 (X = Li, Na) alloys. Density functional theory (DFT) based calculations are carried out first time to compute the physical properties of the alloys. The exchange–correlation potential is solved with modified Becke-Johnson (mBJ) approximation. Structural stability is obtained with ground state optimized lattice parameters, negative formation energy values, and phonon dispersion curves. A brittle nature with an anisotropic character is observed for both alloys. The band structures show a direct bandgap for both alloys, which is also reflected in the density of states. The evaluated optoelectronic response shows the high absorption in the ultraviolet region, confirming their ability to use them in optoelectronic devices. The analysis of thermoelectric parameters shows the high electrical and minimum thermal conductivities for both alloys. The electronic and lattice vibrations dependent high ZT values are achieved for LiAcTe2 and NaAcTe2 alloys. The optoelectronic and thermoelectric responses of the alloys show that they could be promising candidates for use in optoelectronic and renewable energy applications.

Transport and thermoelectric performance of Fluorine functionalized Ge-carbide sheets

Based on density functional theory simulations, GW approximation + BSE and the semi-classical Boltzmann transport theory, electronic ,optical and thermoelectric response of bidimensional fluorinated Ge-carbides are investigated. Three configurations are considered, namely F-CGe, CGe-F, F-CGe-F to explore the effect of both fluorination distribution and coverage. It is shown that the conduction (valence) band is shifted upwards (downwards) when F decorates C-atoms (Ge-atoms) which tunes the gap energy. Furthermore, full fluorination makes CGe sheet better dielectric structure. The maximum reflectivity and absorption reveal that F-CGe-F structure exhibits better optical response, unlike its two counterparts constrained to absorb incident photon energy to the UV region only. The maximum polarization values are found in the visible region for the half fluorinated structure F-CGe and in the UV spectrum for F-CGe-F and CGe-F. The Fluorination also improves the transport properties of CGe which significantly increases its merit factor (ZT) at room temperature. Th three compounds are found to exhibit an ultralow lattice conductivity which leads and a record high ZT up to 0.65, 0.77, and 0.81 at 900 K in CGe-F, F-CGe and F-CGe-F respectively. Our results evaluate the potential of fluorinated CGe sheets as suitable thermoelectric materials at the ambient temperature.

Tailoring the Inherent Magnetism and Thermoelectric Response of Pyrochlore Oxide A2B2O7 (A = Er, B = Ru, Sn, Ge, Pt): A Computational Approach

Tailoring the Inherent Magnetism and Thermoelectric Response of Pyrochlore Oxide A2B2O7 (A = Er, B = Ru, Sn, Ge, Pt): A Computational Approach

Sensitive Room-Temperature Graphene Photothermoelectric Terahertz Detector Based on Asymmetric Antenna Coupling Structure

A highly sensitive room-temperature graphene photothermoelectric terahertz detector, with an efficient optical coupling structure of asymmetric logarithmic antenna, was fabricated by planar micro-nano processing technology and two-dimensional material transfer techniques. The designed logarithmic antenna acts as an optical coupling structure to effectively localize the incident terahertz waves at the source end, thus forming a temperature gradient in the device channel and inducing the thermoelectric terahertz response. At zero bias, the device has a high photoresponsivity of 1.54 A/W, a noise equivalent power of 19.8 pW/Hz1/2, and a response time of 900 ns at 105 GHz. Through qualitative analysis of the response mechanism of graphene PTE devices, we find that the electrode-induced doping of graphene channel near the metal-graphene contacts play a key role in the terahertz PTE response. This work provides an effective way to realize high sensitivity terahertz detectors at room temperature.

Electromagnetic, optical and thermoelectric response of full-Heusler Co2VGe alloy for spintronic and thermoelectric applications: DFT+SOC study

Heusler alloys exhibit diverse functional properties originating from magneto-elastic coupling and attracted significant interest in spintronic applications. We use the full-potential linearized augmented plane wave method to study the electromagnetic, structural, optical and thermoelectric properties of full Heusler Co2VGe alloy. The spin-polarized calculations and the spin-orbit coupling effect (SOC) are carried out to study the properties. The optimization is done in both ferromagnetic and non-magnetic states. The electronic structure shows the full-polarization at the Fermi level and confirms the half-metallic nature of Co2VGe. A band-gap of 0.89eV is achieved in spin-dn states with mBJ and it decreases with SOC up to 0.82eV. The Cobalt-atoms show major contribution to the overall magnetic behavior of the alloy. The optical and the thermoelectric response of Co2VGe are also calculated. In spin-dn states, a high value of Figure of merit i.e. 0.86 is obtained with mBJ and 0.77 with SOC effect at 800 K.

Enhanced thermoelectric and optical response of Ag substituted Cu2O compositions for advanced applications

Cu2O based semiconductor materials are promising candidates for modern electronic devices due to have excellent electronic and optical properties. In this work, pure and Ag doped Cu2O structures were simulated using density functional theory in the framework of wien2k code with generalized-gradient-approximation under full potential linearized augmented plane wave approach. Experimentally, pure and Ag doped Cu2O uniform thin films were successfully fabricated. The morphology and elemental compositions of thin films were investigated using field emission scanning electron microscopy and energy dispersive x-rays spectroscopy, respectively. X-ray diffraction analysis exhibited cubic phase having space-group 224-Pn-3m in all synthesized thin films. Total density of states spectra for Ag containing compositions present overlapping of states at Fermi level. Thermoelectric properties show a significant variation in various parameters with the change in temperature and Ag content in structure. The see-beck coefficient was observed to vary from 0.0002 to 0.00035 Vk−1 for pure and Ag doped Cu2O compositions. The optical parameters like extinction and absorption curves attains maximum values at higher photon energies. The refractive index presents an enhanced transmittance power with the increment in photon energy. The band gap was found to reduce from 2.33 eV to 1.99 eV with Ag doping attributed to the sharp increase in optical conductivity.

Controlled generation and detection of a thermal bias in Corbino devices under the quantum Hall regime

We present an experimental technique to generate and measure a temperature bias in the quantum Hall effect of GaAs/AlGaAs Corbino samples. The bias is generated by injecting an electric current at a central resistive heater, and the resulting radial temperature drop is determined by conductance measurements at internal and external concentric rings. The experimental results agree with the predictions of numerical simulations of the heat flow through the substrate. We also compare these results with previous predictions based on the thermoelectric response of these devices.

Enhanced high-temperature stability of indium tin oxide - Indium oxide thermocouples by two-step annealing

The complex internal structure of the aero-engine and the high-temperature, high-pressure, and high-speed airflow make it difficult to measure the internal temperature. Indium tin oxide (ITO) and In2O3 films have been studied for their application in high-temperature thermocouples and strain gauges. Due to their large Seebeck coefficient and high-temperature stability, ceramic thin-film thermocouples are expected to be used at high-temperature measure. In this paper, ITO-In2O3 thermocouples were fabricated by magnetron sputtering. Besides, the electrical properties of the air-annealed and two-step nitrogen-annealed thermocouples were compared, including the repeatability of thermoelectric response after multiple thermal cycles and the drift rate during the high-temperature duration. The microstructure and electrical conductivity of both the as-deposited and post-annealed ceramic thin films were tested respectively. The result shows that the resitivity and Seebeck coefficient of the thin films annealed in nitrogen is reduced, but the stability at high temperature is greatly improved.

Thermoelectric Performance of n-type Filled Skutterudites RECo4Sb12 Using Rare Earths as Filler Atoms (RE=Nd,Sm,Eu,Yb)

In this work, we perform first-principles calculations based on density functional theory and the semi-classical Boltzmann method to study the structural, mechanical, electronic, and thermoelectric properties of rare Earths filled skutterudites RECo4Sb12 (RE = Nd,Sm,Eu,Yb). It is found that these compounds are n-type semiconductors with high effective mass and narrow bandgap. The main focus here is to investigate the effect of filler rare Earth elements on the thermoelectric response of binary skutterudite CoSb3. In doing so, we compute for each compound the Seebeck coefficient, electrical conductivity, electronic thermal conductivity, and figure of merit in the temperature range from 400 K to 1000 K. The relaxation time and lattice thermal conductivity are calculated as well. Our results reveal that low thermal conductivity and high Seebeck coefficient can be achieved at the same time in RE-filled skutterudites RECo4Sb12, thereby improving their thermoelectric performance which makes them attractive thermoelectric materials at high temperatures.

First principles insights on the structural, mechanical, dynamical, thermoelectric and thermodynamics properties of novel topological (ScSb) semi-metal

In the present report, we have a detailed investigation of the structural, electronic, mechanical, thermoelectric thermodynamic responses of ScSb with external pressure to full potential Linearized augmented Plane-wave technique (FP-LAPW) and semi-classical Boltzmann transport equation based on density functional theory (DFT). Computed the structure of ScSb compound having ground state energy and dynamically stable. Diverse approximations were employed in electronic properties to account for precise exchange and correlation effects. The dynamically and mechanically stability structure is confirmed by the estimation of phonon and elastic constants such as Bulk modulus, Young’s modulus, Poisson's ratio, and shear anisotropy factor. For the transition of carriers from the valence band to conduction, we calculated the electron localized function (ELF), electron, and hole effective mass. Transports properties calculated against temperature, chemical potential, as well as carriers concentrations by employing the external pressure (0GP, 25 GPa, and 40 Gpa) were studied using the semi-classical equation in Boltzmann theory. Thermodynamics properties were computed with external pressure having the variation of temperature in this material which is investigated across a wide temperature range (200–1200 K). Maximum Power factor, electrical conductivity, and thermal conductivity are determined to be 0.3 × 1010 W/mK2s,3 × 1020 (Ω.m.s)-1, and 2.1 × 1015 W/mKs at 300 K against temperature respectively. Because of its non-trivial topological character, this material has a big power factor, which strongly implies that it can operate as a suitable thermoelectric material in the high-temperature zone.

Thermoelectricity in bilayer graphene superlattices

Low-dimensional thermoelectricity is based on the redistribution-accumulation of the electron density of states by reducing the dimension of thermoelectric structures. Superlattices are the archetype of these structures due to the formation of energy minibands and minigaps. Here, we study for the first time the thermoelectric response of gated bilayer graphene superlattices (GBGSLs). The study is based on the four-band effective Dirac Hamiltonian, the hybrid matrix method and the Landauer-Büttiker formalism. We analyze the Seebeck coefficient, the power factor, figure of merit, output power and efficiency for different temperatures and different superlattice structural parameters. We pay special attention to the impact of not only minibands and minigaps on the thermoelectric properties, but also to intrinsic resonances in bilayer graphene structures such as Breit-Wigner, Fano and hybrid resonances. In particular, we analyze the interplay between minibands and Fano resonances as a possible mechanism to improve the thermoelectric response of GBGSLs. We also compute the density of states to know if the redistribution-accumulation of electron states is implicated in the thermoelectric response of GBGSLs.

Probing topological signatures in an optically driven α−T3 lattice

The $\alpha$-$T_3$ lattice, an interpolation model between the honeycomb lattice of graphene($\alpha=0$) and the dice lattice($\alpha=1$), undergoes a topological phase transition across $\alpha=1/\sqrt{2}$ when exposed to a circularly polarized off-resonant light. We study Berry phase mediated bulk magnetic and anomalous thermoelectric responses in order to capture the topological signatures of a driven $\alpha$-$T_3$ lattice. It is revealed that both the Berry curvature and the orbital magnetic moment associated with the flat band change their respective signs across $\alpha=1/\sqrt{2}$. The off-resonant light distorts the flat band near the Dirac points when $0<\alpha<1$ which eventually introduces two distinct well separated forbidden gaps of equal width in the quasienergy spectrum. The orbital magnetization varies linearly with the chemical potential, in the forbidden gaps. The slopes of the linear regions in the orbital magnetization are closely related to the respective Chern numbers on either side of $\alpha=1/\sqrt{2}$. We find that the slope for $\alpha>1/\sqrt{2}$ is approximately two times of that for $\alpha<1/\sqrt{2}$ which essentially indicates a topological phase transition across $\alpha=1/\sqrt{2}$. However, the anomalous Nernst coefficient vanishes when the chemical potential is tuned in the forbidden gaps. The anomalous Hall conductivity in the forbidden gap(s) approaches different quantized values on either side of $\alpha=1/\sqrt{2}$. All these topological signatures can be observed experimentally.

Structural, mechanical, electronic, vibrational and thermoelectric properties of novel double perovskites Ba2MgPdO6 and Ba2MgPtO6 within DFT framework

The first-principles study of novel double perovskites Ba2MgPdO6 and Ba2MgPtO6 has been performed utilizing the concepts of Density Functional Theory (DFT). These materials have been studied for the first time to explore their structural, elastic, electronic, vibrational, thermodynamic and thermoelectric properties. Ba2MgPdO6 and Ba2MgPtO6 possess an FCC (Face centered cubic) crystal structure. The calculated band structure reveals the semiconducting nature of these compounds with the bandgap of 1.18eV and 1.7eV for Ba2MgPdO6 and Ba2MgPtO6 respectively. The elastic stability is predicted based on various calculated mechanical parameters such as Poisson ratio, Bulk modulus and elastic constants. The phonon dispersion curves are analyzed over the high symmetry directions of the Brillouin zone. Phonon vector representation based on Density Functional Perturbation Theory (DFPT) and phonon densities of states indicate the dynamical stability of these compounds. In addition to these properties, the thermoelectric response of Ba2MgPdO6 and Ba2MgPtO6 is investigated with the help of Boltzmann's theory. The figure of merit has been evaluated for both compounds throughout the range from 50 K to 1200 K to analyze their potential for future energy devices. The present study is aimed at providing an overview of many important properties of Ba2MgPdO6 and Ba2MgPtO6 to encourage experimental researchers to synthesize such types of compounds for modern technological devices.

Elastic, electronic, thermal and magnetic investigations of PrX2(X = Fe,Ru) superconductors materials

The structural, elastic, electronic properties, thermal properties and magnetic hyperfine field and thermoelectric response of Laves phase PrFe2 and PrRu2 compounds are researched by using density functional theory via full-potential linear augmented plane waves (FP-LAPW) method within the local orbitals joining the generalized gradient approximation (GGA-PBESol) of exchange-correlation functional as applied in WIEN2k software package. Additionally, the semi-classical Boltzmann theory is utilized to investigate the stress behavior and superconductors applications on magnetic moments of each atom from 0 to 25 GPa for both materials are researched. The GGA-PBESol+U approximation is employed to address the f states of Pr atoms and d states of Fe and Ru atoms. The geometrical analysis of structural parameters is applied. The structural parameters calculated by two approximations are in a good agreement with other results. The calculated elastic constants, Young’s modulus, shear modulus, Poisson’s ratio, sound velocities and Debye temperature are investigated. The thermodynamic properties are calculated by a semi-harmonic Debye model in the pressure range, 0–25 GPa and temperature, 0–1000 K. The partial and total density of states (DOS) are investigated for PrFe2 and PrRu2 compounds. The partial DOS illustrates a hybridized strong at Fermi level. While, the hyperfine magnetic field is determined using two GGA-PBESol and GGA-PBESol+U approximations. Both PrFe2 and PrRu2 have superconducting critical temperatures; 550 K and 580 K, respectively. The comprehensive experimental characterization of PrRu2 is still absent in the literature and superconducting critical-temperature values are favorable with a similar experimental value; 530 K for PrFe2.

Anomalous enhancement of the Nernst effect at the crossover between a Fermi liquid and a strange metal

A strange-metal state appears in many strongly correlated materials, so understanding its nature is a crucial problem in condensed matter physics. This knowledge could provide important insight into high-temperature superconductivity and quantum criticality, but standard Fermi-liquid theory fails in strange metals. Establishing an alternative theory has been a long-standing challenge and fundamental aspects of strange metals—including the nature of their charge carriers—remain elusive. Here we report the observation of a large Nernst response in the strange-metal state in a two-dimensional superconductor 2M-WS2. Specifically, when the system enters the strange-metal state from the Fermi-liquid state, the Nernst coefficient increases to be comparable to the vortex Nernst signal in superconducting cuprates, and it is highly sensitive to carrier mobility. The temperature and magnetic field dependence of the Nernst peak rule out the relevance of both Landau quasiparticles and superconductivity. Instead, the Nernst peak at the crossover indicates a change in carrier entropy when entering the strange-metal state. The presence of such an anomalous Nernst response is further confirmed in other iconic strange metals, suggesting its universality and places experimental constraints on the mechanism of strange metals. The transport behaviour of strange metals is distinct from weakly interacting Fermi liquids. Now, a large thermoelectric response has been shown at the transition between those two states.

Half-metallic behavior Co2YAl (Y= Mo,Tc) compounds

The present manuscript reports structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2MoAl and Co2TcAl full Heusler compounds using first-principle calculations. The full-potential linearized augmented plane wave method within the framework of density functional theory is implemented and WIEN2k code is incorporated in the stable Fm- 3m phase to attain the desired results. The L21 phase is found as the most stable phase for both compounds. The optimized equilibrium lattice parameters in the stable phase are 5.89Å, 5.86Å for Co2MoAl and Co2TcAl respectively. The electronic band structure study proves that both compounds Co2MoAl and Co2TcAl have indirect band gaps of 0.74eV and 0.85eV respectively in majority spin alignment. The half-metallic performance of the present set of compounds is explained by the spin-resolved density of states. The Fermi level at the Brillouin zone point approves the metallic as well as semiconducting behavior. To elucidate the thermodynamical stability of these materials against pressure and temperature by implementing the quasi-harmonic approximation of various parameters like Debye temperature, Gruneisen parameters and specific heat are studied successfully. To know the thermoelectric response, Seebeck coefficient and electrical conductivity are computed using the BoltzTrap code. The thermodynamic profile delivers that the present set of compounds possesses no anomalies with respect to the phase transition or instabilities. The computational study insights that the compounds can be synthesized experimentally and find a route towards spintronic and thermoelectric applicability.

Half-metallic behavior Co2YAl (Y= Mo,Tc) compounds

The present manuscript reports structural stability, half-metallic behavior, thermophysical and thermoelectric properties of Co2MoAl and Co2TcAl full Heusler compounds using first-principle calculations. The full-potential linearized augmented plane wave method within the framework of density functional theory is implemented and WIEN2k code is incorporated in the stable Fm- 3m phase to attain the desired results. The L21 phase is found as the most stable phase for both compounds. The optimized equilibrium lattice parameters in the stable phase are 5.89Å, 5.86Å for Co2MoAl and Co2TcAl respectively. The electronic band structure study proves that both compounds Co2MoAl and Co2TcAl have indirect band gaps of 0.74eV and 0.85eV respectively in majority spin alignment. The half-metallic performance of the present set of compounds is explained by the spin-resolved density of states. The Fermi level at the Brillouin zone point approves the metallic as well as semiconducting behavior. To elucidate the thermodynamical stability of these materials against pressure and temperature by implementing the quasi-harmonic approximation of various parameters like Debye temperature, Gruneisen parameters and specific heat are studied successfully. To know the thermoelectric response, Seebeck coefficient and electrical conductivity are computed using the BoltzTrap code. The thermodynamic profile delivers that the present set of compounds possesses no anomalies with respect to the phase transition or instabilities. The computational study insights that the compounds can be synthesized experimentally and find a route towards spintronic and thermoelectric applicability.

Thermoelectric Response Enhanced by Surface/Edge States in Physical Nanogaps.

Current solid-state thermoelectric converters have poor performance, which typically renders them useless for practical applications. This problem is evidenced by the small figures of merit of typical thermoelectric materials, which tend to be much smaller than 1. Increasing this parameter is then key for the development of functional devices in technologically viable applications that can work optimally. We propose here a feasible and effective design of new thermoelectric systems based on physical gaps in nanoscale junctions. We show that, depending on the type of features, i.e., the character of surface/edge states, on both sides of the gap, it is possible to achieve high figures of merit. In particular, we show that, for configurations that have localized states at the surfaces/edges, which translate into sharp resonances in the transmission, it is possible to achieve large Seebeck coefficients and figures of merit by carefully tuning their energy and their coupling to other states. We calculate the thermoelectric coefficients as a function of different parameters and find non-obvious behaviors, such as the existence of a certain coupling between the localized and bulk states for which these quantities have a maximum. The highest Seebeck coefficients and figures of merit are achieved for symmetric junctions, which have the same coupling between the localized state and the bulk states on both sides of the gap. The features and trends of the thermoelectric properties and their changes with various parameters that we find here can be applied not only to systems with nanogaps but also to many other nanoscale junctions, such as those that have surface states or states localized near the contacts between the nanoscale object and the electrodes. The model presented here can, therefore, be used to characterize and predict the thermoelectric properties of many different nanoscale junctions and can also serve as a guide for studying other systems. These results pave the way for the design and fabrication of stable next-generation thermoelectric devices with robust features and improved performance.

Thermoelectric transport properties of single quantum dot systems in the presence of Majorana states

We present theoretical results for the thermoelectric transport properties in a single quantum dot system side coupled to a Majorana nanowire. The system’s electrical conductivity G , and the fundamental thermoelectric parameters such as the Seebeck coefficient S and thermal conductivity κ are numerically estimated based on a linear response approximation. Our results prove that the Majorana states in the side nanowire play an important role in the system’s thermoelectric response. In particular, a proper choice of the quantum dot — Majorana nanowire tunneling rate ξ and of the Majorana states overlap amplitude ɛ M can provide the appropriate physical environment for the experimental detection of Majorana states via thermoelectrical experimental measurements. • We considered the effects of Majorana states on the thermoelectric response of a single quantum dot system. • We present numerical results for the system electrical conductivity, Seebeck coefficient, thermal conductivity, and figure of merit. • The system thermoelectric response is strongly dependent on the quantum dot — Majorana nanowire tunneling rate ξ and of the Majorana states overlap amplitude ɛ M .