Electronic Part Of Thermal Conductivity Research Articles

Effect of Pressure on Thermoelectric Performance of Half Heusler Compounds

In this work, the density functional theory (DFT) combined with Boltzmann transport equations are used to explore the effect of pressure on the structural, mechanical, thermal, and electronic properties of two half Heusler compounds PdXSn (X = Zr,Hf). The electronic band structure is tuned under pressure which enhances the thermoelectric properties of both compounds. The band gap opens with pressure and its value is 0.91 eV (1.26) for PdZrSn and 0.82 eV (1.16 eV) for PdHfSn at 0GPa (30GPa). The indirect nature does not alter at any pressure. The seebeck coefficient enhances from 900 μV/K to 1161 μV/K for PdZrSn and from 763 μV/K to 1012 μV/K for PdHfSn at pressure 0GPa to 30GPa. Similar trends observed in case of electrical conductivity and electronic part of thermal conductivity. But the lattice thermal conductivity is reduced from15.16 W/mKto 12.51 W/mK for PdZrSn and from 9.53 W/mK to 8.34 W/mK for PdHfSn at 30GPa respectively. Overall, the figure of merit ZT is elevated and attained maximum value of 0.45(0.55) for PdZrSn (PdHfSn) under pressure up to 30GPa.

Investigating the effect of electronic correlation on transport properties and phononic states of Vanadium

In the present work, we have tried to investigate the importance of electronic correlation on transport properties and phononic states of Vanadium (V). The temperature-dependent electrical resistivity (ρ) and electronic part of thermal conductivity (κe) due to electron–electron interactions (EEIs) and electron–phonon interactions (EPIs) are computed. The values of ρ due to EEIs are found to be extremely small in comparison to ρ due to EPIs. For instance, at 300 K, the calculated value of ρ due to EEIs (EPIs) is ∼0.859×10−3 (∼0.20) μΩ m. The magnitudes of κe due to EPIs are found to be in good agreement with the experimental results. These observations indicate the negligible importance of EEIs to these quantities for V. However, at 300 K, the value of Seebeck coefficient (S) at DFT+DMFT level (∼−0.547 μV K−1) is found to be entirely different than at DFT level (∼7.401μV K−1). Also, the DFT+DMFT value of S at 300 K is in good match with the available experimental data (−1.06 μV K−1[1], 1.0 μV K−1[2]). Apart from this, the study of phononic states at DFT and DFT+DMFT level is performed. The obtained phononic band structure and phonon DOS at DFT+DMFT differ to a good extent from that at DFT. The maximum energy of phononic state obtained at DFT (DFT+DMFT) is ∼ 33.83 (∼35.15) meV, where the result of DFT+DMFT is obtained more closer to the experimental data (35.15 [3], 36.98 [4] & 41.77 [5] meV). These results highlight the importance of electronic correlation on S & phononic states of simple correlated V metal.

TRACK: A python code for calculating the transport properties of correlated electron systems using Kubo formalism

Exploring the transport properties of different materials brings new avenue for basic understanding of emergent phenomena and practical applications in many different fields. Here, we report a program named as TRACK (TRAnsport properties for Correlated materials using Kubo formalism) which is written in Python 3 for calculating temperature dependent electrical conductivity, electronic part of thermal conductivity, Seebeck coefficient and Lorenz number. In this code, Kubo linear-response formalism is utilized for computing these parameters using both interacting and non-interacting electronic structure methods. The formula for transport coefficients is accordingly modified to obtain the transport parameters under relaxation time approximation using band-theory. The basic inputs of this program are the structural information, dense k-points sampling in the irreducible part of the Brillouin zone and the information of velocity matrix elements, which can be calculated using third-party ab-initio package. TRACK is expected to calculate the transport properties of different class of materials. The code has been benchmarked by performing calculation on three different types of materials namely Vanadium (V), FeSi and LaCoO3, which are metal, semiconductor and Mott insulator, respectively. The temperature dependent behaviour of the transport coefficients for these materials show fairly good agreement with the corresponding experimental data. Program summaryProgram Title: TRACKCPC Library link to program files:https://doi.org/10.17632/jdt9tfkt4v.1Developer's repository link:https://sourceforge.net/projects/track-code/files/TRACK.zip/downloadLicensing provisions: GPLv3Programming language: Python3External routines/libraries: NumPy, SciPy, TimeNature of problem: Calculating the transport parameters using the Kubo linear-response formalism.Solution method: We present a Python3 open source code for calculating transport coefficients using Kubo formalism. Both interacting and non-interacting electronic structure methodology are possible to be used for computing transport parameters.

First-Principles Investigations of Thermoelectric Behavior of RuCrX (X = Si, Ge, Sn).

The half-Heusler alloys have not only been recognized for spintronic and memory devices but also for thermoelectric applications. In this research work, the detailed study for thermoelectric parameters of RuCrX (X = Si, Ge, Sn) half-Heusler alloys has been carried out by using the pseudopotential approach alongside the Boltzmann transport theory. The RuCrX (X= Si, Ge, Sn) was reported stable in C1 b -type structure by means of energy-volume optimization, elastic stability criteria, positive phonon frequencies in phonon dispersion curves, and formation energies. The all important thermoelectric properties of these alloys have not yet been explored. The thermoelectric properties such as Seebeck coefficient, electronic part of thermal conductivity, electrical conductivity, and power factor have been discussed within a specific temperature range (300-1200 K). The calculated value of the power factor was found to be 5.11 × 1011 W/(m K2 s) for RuCrSi, 3.42 × 1011 W/(m K2 s) for RuCrGe, and 1.85 × 1011 W/(m K2 s) for RuCrSn at 1200 K.

Effect of pressure on structural, electronic dispersion relations, optical and thermoelectric properties of CsNbO3 perovskite for photovoltaic and energy applications

The perovskites have not only been recognized for memory devices and spintronic applications but are equally important for the thermoelectric response calculations. In this research work, the effect of pressure on structural, electronic dispersion curves, optical and thermoelectric parameters of CsNbO3 cubic perovskite have been investigated by using the pseudopotential approach alongside the Boltzmann transport theory. The CsNbO3 was reported stable in simple cubic structure by means of energy-volume optimization and phonon dispersion curves by B. Sabir et. al. CsNbO3 is reported as the direct band gap semiconductor with band gap around 1.95 eV at ambient pressure. Interestingly the band gap decrease with the increase in the pressure. The absence of negative phonon frequency shows the dynamical stability of this material under pressure. The analysis of imaginary part of dielectric response function predicts the utility of this perovskite in high frequency microwave sensors as well as the optoelectronic devices like optical sensors and interconnects. Further, the thermoelectric parameters such as Seebeck coefficient (S), electronic part of thermal conductivity (κe/τ), electrical conductivity (σ/τ) and power factor (PF) have been discussed within a specific temperature and pressure range (300–1200 K) and (10–50 GPa) respectively. The calculated values of power factor and optical constants prove it a potential candidate for thermoelectric and photovoltaic applications.

Experimental and computational approaches to study the high temperature thermoelectric properties of novel topological semimetal CoSi

Here, we study the thermoelectric properties of topological semimetal CoSi in the temperature range 300–800 K by using combined experimental and density functional theory (DFT) based methods. CoSi is synthesized using arc melting technique and the Rietveld refinement gives the lattice parameters of a = b = c = 4.445 Å. The measured values of Seebeck coefficient (S) shows the non-monotonic behaviour in the studied temperature range with the value of ∼−81 μV K−1 at room temperature. The |S| first increases till 560 K (∼−93 μV K−1) and then decreases up to 800 K (∼−84 μV K−1) indicating the dominating n-type behaviour in the full temperature range. The electrical conductivity, σ (thermal conductivity, κ) shows the monotonic decreasing (increasing) behaviour with the values of (12.1 W m−1 K−1) and (14.2 W m−1 K−1) Ω−1 m−1 at 300 K and 800 K, respectively. The κ exhibits the temperature dependency as, κ ∝ T 0.16. The DFT based Boltzmann transport theory is used to understand these behaviour. The multi-band electron and hole pockets appear to be mainly responsible for deciding the temperature dependent transport behaviour. Specifically, the decrease in the |S| above 560 K and change in the slope of σ around 450 K are due to the contribution of thermally generated charge carriers from the hole pockets. The temperature dependent relaxation time (τ) is computed by comparing the experimental σ with calculated σ/τ and it shows temperature dependency of 1/T 0.35. Further this value of τ is used to calculate the temperature dependent electronic part of thermal conductivity (κ e) and it gives a fairly good match with the experiment. Present study suggests that electronic band-structure obtained from DFT provides a reasonably good estimate of the transport coefficients of CoSi in the high temperature region of 300–800 K.

Anab initio study of topological and transport properties of YAuPb

In the last few decades, the study of topological materials has been carried out on an extensive scale. Half-Heusler alloys are well known for their topological behaviours. In this work, we present a detailed study of topological properties of a ternary half-Heusler alloy, YAuPb, using the tight-binding approach. We have calculated some important topological properties which includes—finding nodes and their chiralities, Berry curvature (Ω) and the surface-states. Five pairs of characteristic nodes with equal and opposite chiralities are obtained. Based on the study of these properties, we categorise the material as non-trivial topological semimetal. Besides the topological behaviours, we present a comparative study of temperature dependent transport properties corresponding to the chemical potential (μ) of the Fermi level and the node points. The temperature range chosen for the study is 50–300 K. The results obtained from the calculations of electrical conductivity per unit relaxation time ( σ /τ) and the electronic part of thermal conductivity per unit relaxation time ( κ 0) indicates the conducting nature of the material to both the heat and electricity. At the Fermi level, the value of Seebeck coefficient (S) is found to be ∼−9.07(−35.95) μV K−1 at 50(300) K. The negative value of S indicates the n-type behaviour of the compound. The calculated value of electronic specific heat (Pauli magnetic susceptibility) corresponding to Fermi level is ∼0.03(0.18) × 10−2 J mol−1 K−1 (∼1.21(1.14) × 10−10 m3 mol−1) at 50(300) K. This work suggests that YAuPb is a promising candidate of non-trivial topological semimetals which can be employed in transmission of heat and electricity, and as n-type material within the temperature range of 50–300 K.

The half metallic feature at high temperature of the novel half-Heusler alloys and their [100] oriented layered superlattices: A DFT investigations

Herein, we have investigated by means of the DFT calculations the magneto-electronic properties and thermoelectric responses of the novel half-Heusler NbFe(Mn)Sn compounds and their layered superlattices growing along [100] direction. The ground-state properties and magnetic stability revealed that the bulk compounds were ferromagnetic materials. The formation energy was determined meticulously and revealed that the studied materials could be synthesized experimentally. The half-metallic ferromagnetism with the presence of the strong p-d hybridization have been strongly confirmed from the magneto-electronic calculations for all the studied materials. The Curie temperature was estimated from the mean field approach, the obtained values exceed the ambient temperature. Furthermore, the thermoelectric response was evaluated and categorized the investigated compounds as a good thermoelectric materials due to the high figure of merit, large Seebeck coefficient and low electronic part of thermal conductivity. The curve of spin polarization (SP) as a function of temperature divulged that the 100% SP was conserved at high temperature for NbFeSn and superlattice materials. The phonon dispersion was calculated in order to examine the dynamic stabilities of the studied materials. The present detailed study made these materials as a potential candidates for spintronic thermoelectric devices.

Thermoelectric power properties of Ge doped PbTe alloys

In this work, stoichiometric Pb1−xGexTe (x = 0.0, 0.03, 0.06, 0.09, 0.12) crystalline alloys were synthesized using the monotonical temperature melting technique. The synthesized alloys were examined using x-ray diffraction and scanning electron microscope. It was revealed that the crystal structure in all samples is a cubic phase of PbTe. In terms of Seebeck coefficient and electrical conductivity, thermoelectric measurements were carried out in the temperature range of 83–373 K. The Seebeck coefficient of the compounds showed a positive sign, which refers to p-type conduction. The thermoelectric power factor (PF) was studied as a function of temperature, with different amounts of Ge content (x). The highest PF was recorded for the highly Ge-doped samples at higher temperatures (373 K). The maximum PF was observed at 3.2 × 102 µW/m K2 for the sample with x = 0.09, which is quite high for the studied compounds. The electronic part of thermal conductivity was calculated using the Wiedemann-Franz law. A noticeable reduction of this thermal conductivity was detected due to stronger point defect scattering introduced by Ge doping. The reduction in the electronic thermal conductivity can led to a considerable enhancement in the thermoelectric figure of merit.

Fractional exponents of electrical and thermal conductivity of vanadium intercalated layered 2H-NbS2 bulk crystal

Intercalation of transition metal dichalcogenides (TMDs) by 3d or 4d transition metal elements are of considerable interest as the intercalated atoms can finely tune the physical and chemical properties of host TMDs. On addition, these intercalation complexes show interesting magnetic property and displays anomalous transport behavior at the magnetic ordering temperature. Here, we have synthesized and measured transport properties of single crystal vanadium intercalated Niobium Di-sulphide. At 300 K, electrical resistivity and thermal conductivity of V $$_{0.3}$$ NbS $$_{2}$$ is found to be $$\sim $$ 10 $$^{-6}$$ $$\Omega $$ m and 36 W m $$^{-1}$$ K $$^{-1}$$ respectively. Unlike phonon scattering, the spin scattering is found to affect both electrical and phonon conduction at low temperature. The electrical resistivity at temperature $${T} < 45\,\hbox {K}$$ follows $$T^{3/2}$$ behavior, whereas the electronic part of thermal conductivity shows exponent of 0.8. Using steady-state method, the temperature dependent lattice part of thermal conductivity shows exponents of 0.5 and − 0.5 at $${T} < 45\,\hbox {K}$$ and $${T} > 45\,\hbox {K}$$ respectively. Moreover, the peak of the total thermal conductivity also overlaps with the magnetic transition temperature, indicating the participation of spin dependent phonon dynamics below 45 K.

Prediction of a new quaternary Heusler alloy within a good electrical response at high temperature for spintronics applications: DFT calculations

AbstractLately, the Heusler alloys have been gained an enormous technological attention due to their half‐metallic ferromagnets (HMFs) behavior making them technologically promising for spintronics devices. Herein, we have investigated by means of the linearized augmented plane wave method within full potential for determining several physical properties of the new hypothetical Ti‐based quaternary Heusler alloy RhZrTiAl. The ground‐state properties and magnetic stability revealed that the compound was ferromagnetic material and crystallizes in Type I structure. The formation energy and transition pressure from stable to metastable phase were determined meticulously and revealed that the studied compound, has a stable structure at high pressure, could be synthesized experimentally. The elastic constants and the related mechanical properties were investigated and divulged that this compound was stable against any elastic deformations, which classified it as an anisotropic ductile material. The HMF behavior, with the presence of the strong p‐d hybridization, has been strongly confirmed from the magneto‐electronic calculations. Furthermore, the thermoelectric response was evaluated and categorized the investigated compound as a good thermoelectric material due to the high figure of merit, large Seebeck coefficient and low electronic part of thermal conductivity. The curve of DOS as a function of temperature divulged that the half metallic behavior was conserved at high temperature. The present detailed study made this compound as a potential candidate for spintronics thermoelectric devices.

Thermoelectric properties of YSb: A first-principles approach

The electronic and thermoelectric properties of YSb have been investigated using Full Potential Linearized Augmented Plane wave method (FP-LAPW) based on density functional theory (DFT) in combination with semi-classical Boltzmann transport equation. The exchange and correlation effects have been taken into account by generalized gradient approximation (GGA) within Perdew-Burke-Ernzerhof (PBE) parameterization. The calculated elastic constants such as Bulk modulus, Young modulus, Poisson’s ratio and shear anisotropy factor confirm the mechanical stability of this compound. Boltzmann transport equations were used for the calculation of electronic part of thermoelectric transport parameters such as Seebeck coefficient, Power factor, electrical conductivity and electronic part of thermal conductivity as a function of chemical potential. The temperature dependence of thermoelectric properties of this material at pressure ∼12 GPa is studied over wide range of temperature (200–1200 K). The calculated value of power factor, electrical conductivity and thermal conductivity at T = 1200 K are found to be 65.92 × 1010 W K−2 cm−1 sec−1, 2.90 × 1020 S cm−1sec−1 and 0.97 × 1016 W m−1K−1 sec−1, respectively. The large value of power factor which is due to its non-trivial topological nature strongly suggests that this material can act as a good thermoelectric material in high temperature region.

Thermoelectric properties of heavy fermion CeRhIn5 using density functional theory combined with semiclassical Boltzmann theory.

Experimental evidences show that Ce-based compounds can be good candidates for thermoelectric applications due to their high thermoelectric efficiencies at low temperatures. However, thermoelectric properties have been studied less than the other properties for CeRhIn5, a technologically and fundamentally important compound. Thus, we comprehensively investigate the thermoelectric properties, including the Seebeck coefficient, electrical conductivity, electronic part of thermal conductivity, power factor and electronic figure of merit, by a combination of quantum mechanical density functional and semiclassical Boltzmann theories, including relativistic spin–orbit interactions using different exchange–correlation functionals at temperatures T ≤ 300 K for CeRhIn5 along its a and c crystalline axes. The temperature dependences of the thermoelectric quantities are investigated. Our results reveal a better Seebeck coefficient, electrical conductivity, power factor and thermoelectric efficiency at T ≪ 300, in agreement with various other Ce-based compounds, when a high degree of localization is considered for the 4f-Ce electrons. The Seebeck coefficient, power factor and thermoelectric efficiency are made more efficient near room temperature by decreasing the degree of localization for 4f-Ce electrons. Our results also show that the thermoelectric efficiency along the a crystalline axis is slightly better than that of the c axis. We also investigate the effects of hydrostatic pressure on the thermoelectric properties of the compound at low and high temperatures. The results show that the effects of imposing pressure strongly depend on the degree of localization considered for 4f-Ce electrons.

Thermal transport studies on charge density wave materials LaPt2Si2 and PrPt2Si2

We measured the thermal properties of polycrystalline samples of LaPt2Si2 and PrPt2Si2 using thermopower (S) along with thermal conductivity (κ) in the temperature range 10 K–300 K. Significant anomalies related to charge density waves (CDW) around 112 K and 88 K respectively have been observed in in both systems. Analysis of thermopower by a two band model suggests that the observations are consistent with a reduction of electron charge density. A change in slope accompanied by a drop in the value of thermal conductivity has been observed around TCDW in case of LaPt2Si2. Analysis of thermal conductivity of this material suggests that the CDW mainly affects electronic contribution to thermal transport. Only a slight change of slope has been detected in temperature dependent thermal conductivity in the case of PrPt2Si2 around TCDW, while its resistivity shows a clear anomaly which shows that electronic part of thermal conductivity is mainly influenced by the CDW in this case also. It is interesting to note that the lattice contribution to thermal conductivity remains unaffected by the CDWs in both materials.

Temperature dependent electronic transport in concentrated solid solutions of the 3d -transition metals Ni, Fe, Co and Cr from first principles

An approach previously developed for the calculation of transport coefficients via the Mott relations is applied to the calculation of finite temperature transport properties of disordered alloys---electrical resistivity and the electronic part of thermal conductivity. The coherent-potential approximation is used to treat chemical disorder as well as other sources of electron scattering, i.e., temperature induced magnetic moment fluctuations and lattice vibrations via the alloy analogy model. This approach, which treats all forms of disorder on an equal first-principles footing, is applied to the calculation of transport properties of a series of fcc concentrated solid solutions of the $3d$-transition metals Ni, Fe, Co, and Cr. For the nonmagnetic alloys ${\mathrm{Ni}}_{0.8}{\mathrm{Cr}}_{0.2}$ and ${\mathrm{Ni}}_{0.33}{\mathrm{Co}}_{0.33}{\mathrm{Cr}}_{0.3}$, the combined effects of chemical disorder and electron-lattice vibrations scattering result in a monotonic increase in the resistivity as a function of temperature from an already large, $T=0$, residual resistivity. For magnetic ${\mathrm{Ni}}_{0.5}{\mathrm{Co}}_{0.5},{\mathrm{Ni}}_{0.5}{\mathrm{Fe}}_{0.5}$, and ${\mathrm{Ni}}_{0.33}{\mathrm{Fe}}_{0.33}{\mathrm{Co}}_{0.33}$, the residual resistivity of which is small, additional electron scattering from temperature induced magnetic moment fluctuations results in a further rapid increase of the resistivity as a function of temperature. The electronic part of the thermal conductivity in nonmagnetic ${\mathrm{Ni}}_{0.8}{\mathrm{Cr}}_{0.2}$ and ${\mathrm{Ni}}_{0.33}{\mathrm{Co}}_{0.33}{\mathrm{Cr}}_{0.33}$ monotonically increases with temperature. This behavior is a result of the competition between a reduction in the conductivity due to electron-lattice vibrations scattering and temperature induced increase in the number of carriers. In the magnetic alloys, electron scattering from magnetic fluctuations leads to an initial rapid decrease in thermal conductivity until this is overcome by an increasing number of carriers at temperatures slightly below the Curie temperature. Similar to the resistivity above ${T}_{C}$, the electronic parts of the thermal conductivities are close to each other in all alloys studied.

Structural, electronic and thermoelectric properties of bulk and monolayer of Sb2Se3 under high pressure: By GGA and mBJ approaches

The effects of high pressure on the structural, electronic and thermoelectric properties of Sb2Se3 have been studied by using FP-LAPW method combined with Boltzmann transport theory. The variation of lattice constants, band structure, density of states, seebeck coefficient, electrical conductivity, electronic part of thermal conductivity and figure of merit (ZT) with pressure (up to 45.2 GPa) are calculated. Our results show that Sb2Se3 has a direct band gap of 1.43 eV in the bulk structure and it has an indirect band gap of 0.4 eV in the monolayer structure, at zero pressure. Increasing pressure led to a decrease in the band gap value and the nature of the band gap shifts from direct to the indirect. With the increase in pressure, the seebeck coefficient, electrical conductivity and electronic part of thermal conductivity increase and ZT decreases. The maximum ZT of 1.12 was achieved at 800 K, n = 1019 per cm−3 for n -type doping. Hence, Sb2Se3 is a good candidate for thermoelectric applications. The obtained results are in close agreement with the experimental results.

Thermoelectric properties of AgSbTe2 from first-principles calculations

The structural, electronic, and transport properties of AgSbTe2 are studied by using full-relativistic first-principles electronic structure calculation and semiclassical description of transport parameters. The results indicate that, within various exchange-correlation functionals, the cubic Fd3¯m and trigonal R3¯m structures of AgSbTe2 are more stable than two other considered structures. The computed Seebeck coefficients at different values of the band gap and carrier concentration are accurately compared with the available experimental data to speculate a band gap of about 0.1–0.35 eV for AgSbTe2 compound, in agreement with our calculated electronic structure within the hybrid HSE (Heyd-Scuseria-Ernzerhof) functional. By calculating the semiclassical Seebeck coefficient, electrical conductivity, and electronic part of thermal conductivity, we present the theoretical upper limit of the thermoelectric figure of merit of AgSbTe2 as a function of temperature and carrier concentration.

Thermal conductivity and viscosity of liquid CdTe: A theoretical study

Cadmium telluride (CdTe) is a widely used semiconductor, having applications as gamma-ray detector as well as excellent photorefractive and electrooptic characteristics in the infrared. It is also used as a substrate for HgCdTe for the detection of infrared radiation. These applications generally require large high-quality crystals containing minimum quantities of defects such as grain boundaries, dislocations, and residual impurities. In this work, the authors estimate the temperature-dependent thermal conductivity and liquid CdTe, as well as the kinematic viscosity of CdTe and several other liquid semiconductors at melting. Both of these properties are necessary inputs in models of crystal growth. To estimate the viscosity, and the molecular contribution to the thermal conductivity, they use both a hard-sphere model in combination with a transformed Debye formula. The electronic part of thermal conductivity is calculated from the Wiedemann-Franz law.