Lead and tin chalcogenides have been studied widely due to their promising thermoelectric (TE) properties. Further enhancement in their TE efficiency has been reported upon the reduction of the dimension, which is an important feature in modern device fabrications. Using density functional theory combined with the Semi-classical Boltzmann transport theory, we studied the structural, electronic and TE properties of two-dimensional (2D) MX (M = Sn, Pb; X = S, Te) monolayers. Spin-orbit coupling was found to have significant effects on their electronic structure, particularly for the heavy compounds. Structural optimization followed by phonon transport studies prevailed that the rectangular (γ-) phase is energetically the most favorable for SnS and SnTe monolayers, whereas the square structure is found the most stable for PbS and PbTe monolayers. Our results are in good agreement with previous studies. These 2D materials exhibit high Seebeck coefficients and power factors along with low lattice thermal conductivities, which are essential features of good TE materials. The maximum figure of merits (ZT) of 1.04, 1.46, 1.51 and 1.94 are predicted for n-type SnS, SnTe, PBS and p-type PbTe monolayers respectively at 700 K, which are higher than their bulk ZT values. Hence, these monolayers are promising candidates for TE applications.
The layered Bi-chalcogenide compounds have been drawing much attention as a new layered superconductor family since 2012. Due to the rich variation of crystal structure and constituent elements, the development of new physics and chemistry of the layered Bi-chalcogenide family and its applications as functional materials have been expected. Recently, it was revealed that the layered Bi chalcogenides can show a relatively high thermoelectric performance (ZT = 0.36 in LaOBiSSe at ~650 K). Here, we show the crystal structure variation of the Bi-chalcogenide family and their thermoelectric propert…
In-plane thermal conductivity of the thermoelectric layered cobalt oxides has been measured using the Harman method, in which thermal conductivity is obtained from temperature gradient induced by applied current. We have found that the charge reservoir block (the block other than the CoO$_2$ block) dominates the thermal conduction, where a nano-block integration concept is effective for material design. We have further found that the thermal conductivity shows a small but finite in-plane anisotropy between $a$ and $b$ axes, which can be ascribed to the misfit structure.
Inspired by the recent first-principles calculations showing the high thermoelectric performance of layered pnictogen chalcogenides, we experimentally characterise the crystal structure and high-temperature transport properties of the layered antimony selenides REOSbSe2 (RE = La, Ce). The crystal structure of REOSbSe2 was the tetragonal P4/nmm space group, consisting of alternate stacks of SbSe2 and REO layers. These two compounds were n-type semiconductors. The optical band gaps of LaOSbSe2 and CeOSbSe2 were evaluated to be 1.0 and 0.6 eV, respectively. The room-temperature thermal conductivi…
Layered-antiferromagnetic compound CuCrS2 has been prepared by different methods. The analysis of X-ray diffraction patterns of different samples gave significant amount of vacancy-disorder of Cr-atoms within the layers. Extended period of sintering above 9000C increases the transfer of Cr-atoms to the interstitial sites between the layers. This disorder has marginal effect on the Antiferromagnetic properties. The electrical conductivity is increased and the thermoelectric power remains positive and quite high between 150-400\muV/K in the paramagnetic state around room temperature with increas…
Experimental results have shown that the quaternary compound Cu2ZnSnSe4 is an excellent thermoelectric material. This inspires us to seek the other quaternary compounds with similar chemical formula to Cu2ZnSnSe4 as thermoelectric materials. In this paper, we use the first-principle method to systematically explore the electronic and phonon structures, mechanical, thermal and thermoelectric properties of p- and n-type Ag2XYSe4 (X=Ba, Sr; Y=Sn, Ge). It is found that the ZT maximum for n-type Ag2SrGeSe4 can reach up to 1.22 at 900 K, and those for p-type Ag2SrSnSe4, Ag2SrGeSe4 and Ag2BaSnSe4 can…
Thermoelectric power generation has been recognized as one of the most important technologies, and high-performance thermoelectric materials have long been pursued. However, because of the large number of candidate materials, this quest is extremely challenging, and it has become clear that a firm theoretical concept from the viewpoint of band-structure engineering is needed. In this study, we theoretically demonstrate that pnictogen-dichalcogenide layered compounds, which originally attracted attention as a family of superconductors and have recently been investigated as thermoelectric materi…
Although SbSe2-based layered compounds have been predicted to be high-performance thermoelectric materials and topological materials, most of these compounds obtained experimentally have been insulators so far. Here, we present the effect of Bi substitution on the thermoelectric properties of SbSe2-based layered compounds NdO0.8F0.2Sb1-xBixSe2 (x = 0-0.4). The room temperature electrical resistivity is decreased to 8.0 * 10^-5 ohmm for x = 0.4. The electrical power factor is calculated to be 1.4 * 10^-4 W/mK^2 at 660 K, which is in reasonable agreement with combined Jonker and Ioffe analysis. …
We predict high thermoelectric efficiency in the layered perovskite La$_2$Ti$_2$O$_7$, based on calculations (mostly ab-initio) of the electronic structure, transport coefficients, and thermal conductivity in a wide temperature range. The figure of merit $ZT$ computed with a temperature-dependent relaxation time increases monotonically from just above 1 at room temperature to over 2.5 at 1200 K, at an optimal carrier density of around 10$^{20}$ cm$^{-3}$. The Seebeck thermopower coefficient is between 200 and 300 $μ$V/K at optimal doping, but can reach nearly 1 mV/K at low doping. Much of the …
Thermoelectricity is a promising avenue for harvesting energy but large-scale applications are still hampered by the lack of highly-efficient low-cost materials. Recently, Fe$_2YZ$ Heusler compounds were predicted theoretically to be interesting candidates with large thermoelectric power factor. Here, we show that under doping conditions compatible with thermoelectric applications, these materials are prone to an unexpected magnetic instability detrimental to their thermoelectric performance. We rationalize the physics at the origin of this instability, provide guidelines for avoiding it and d…
We report the synthesis and thermoelectric transport properties of As-doped layered pnictogen oxyselenides NdO0.8F0.2Sb1-xAsxSe2 (x < 0.7), which are predicted to show high-performance thermoelectric properties based on first-principles calculation. The crystal structure of these compounds belongs to the tetragonal P4/nmm space group (No. 129) at room temperature. The lattice parameter c decreases with increasing x, while a remains almost unchanged among the samples. Despite isovalent substitution of As for Sb, electrical resistivity significantly rises with increasing x. Very low thermal cond…
Nanostructured materials have emerged as an alternative to enhance the figure of merit (ZT) of thermoelectric (TE) devices. Graphene exhibits a high electrical conductivity (in-plane) that is necessary for a high ZT; however, this effect is countered by its impressive thermal conductivity. In this work TE layered devices composed of electrochemically exfoliated graphene (EEG) and a phonon blocking material such as poly (3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS), polyaniline (PANI) and gold nanoparticles (AuNPs) at the interface were prepared. The figure of merit, ZT, of each…
The unique structure of Zintl phase makes it an ideal system to realize the concept of phonon-glass and electron-crystal in the thermoelectric community. In this work, by combining first-principles calculations and Boltzmann transport theory for both electrons and phonons, we demonstrate that the ZT value of Zintl compound KSnSb can reach ~2.6 at 800 K. Such extraordinary thermoelectric performance originates from the large Seebeck coefficient due to multi-valley band structures and particularly very small lattice thermal conductivity caused by mixed-bond characteristics.
The electronic and transport properties of the half-Heusler compound LaPtSb are investigated by performing first-principles calculations combined with semi-classical Boltzmann theory and deformation potential theory. Compared with many typical half-Heusler compounds, the LaPtSb exhibits obviously larger power factor at room temperature, especially for the n-type system. Together with the very low lattice thermal conductivity, the thermoelectric figure of merit (ZT) of LaPtSb can be optimized to a record high value of 2.2 by fine tuning the carrier concentration.
Improving the thermoelectric efficiency is one of the greatest challenges in materials science. The recent discovery of excellent thermoelectric performance in simple orthorhombic SnSe crystal offers new promise in this prospect [Zhao et al. Nature 508, 373 (2014)]. By calculating the thermoelectric properties of orthorhombic IV-VI compounds GeS,GeSe,SnS,and SnSe based on the first-principles combined with the Boltzmann transport theory, we show that the Seebeck coefficient, electrical conductivity, and thermal conductivity of orthorhombic SnSe are in agreement with the recent experiment. Impo…
We have performed systematic density functional calculations and evaluated thermoelectric properties, See- beck coefficient and anomalous Nernst coefficient of half-Heusler comounds CoMSb(M=Sc, Ti, V, Cr, and Mn). The carrier concentration dependence of Seebeck coefficients in nonmagnetic compounds are in good agreement with experimental values. We found that the half-metallic ferromagnetic CoMnSb show large anomalous Nernst effect originating from Berry curvature at the Brillouin zone boundary. These results help to understanding for the mechanism of large anomalous Nernst coefficient and giv…
In order to improve the thermoelectric performance of TiCoSb we have substituted 50% of Ti equally with Zr and Hf at Ti site and Sb with Sn and Se equally at Sb site. The electronic structure of Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 is investigated using the full potential linearized augmented plane wave method and the thermoelectric transport properties are calculated on the basis of semi-classical Boltzmann transport theory. Our band structure calculations show that Ti0.5Zr0.25Hf0.25CoSn0.5Se0.5 has semiconducting behavior with indirect band gap value of 0.98 eV which follow the empirical rule of 18…
We present a study of the electronic properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.589 eV and 0.538 eV, respectively and are in agreement with the available experimental data. To compare the thermoelectric properties of the different compounds we calculate their thermopower using Mott's law and show, as expected experimentally, that the substituted telluride…
The electronic and transport properties of CuInTe2 chalcopyrite are investigated using density functional calculations combined with Boltzmann theory. The band gap predicted from hybrid functional is 0.92 eV, which agrees well with experimental data and leads to relatively larger Seebeck coefficient compared with those of narrow-gap thermoelectric materials. By fine tuning the carrier concentration, the electrical conductivity and power factor of the system can be significantly optimized. Together with the inherent low thermal conductivity, the ZT values of CuInTe2 compound can be enhanced to …
We analyze the anisotropic electrical and thermal transport measurements in single crystals of In2Te5 belonging to monoclinic space group C12 c1 with the temperature gradient applied parallel and perpendicular to the crystallographic c-axis of the crystals. The thermal conductivity along the c-axis thermal conductivity parallel was found to smaller by a factor of 2 compared to the thermal conductivity along the direction perpendicular to the c-axis over the entire temperature range. In contrast, the Seebeck coefficient along the c-axis parallel was found to be higher than its value along the d…
We report the structural, mechanical, electronic, optical, thermoelectric properties and spectroscopic limited maximum efficiency (SLME) of oxide double perovskite structure Ba2SbNbO6 and Ba2SbTaO6 compounds. All the investigations were performed through the first-principles density functional theory (DFT). The obtained values for the elastic constants reveal the mechanical stability of the studied compounds. The calculated data of bulk modulus (B), shear modulus (G), and Young's modulus (E) for Ba2SbTaO6 are found to be greater than those of Ba2SbNbO6. The ratio of Bulk to shear ratio (B/G) s…
Crystallographic data and thermoelectric properties (from 240 K up to 380 K) of Yb3Co4Ge13, Yb3Co4Sn13 compounds and Yb2CeCo4Ge13 and Yb2.3La0.7Co4Ge13 solid solutions are reported. The Seebeck coefficients, electric resistance and thermal conductivity increase monotonically with increasing temperature from 240 to 380 K for all the compounds. The Seebeck coefficient is S = 14 - 27 μV//K for Yb3Co4Sn13, and S = -21 -- -12 μV/K for Yb3Co4Ge13. The substitution of Yb for cerium or lanthanum in Yb3Co4Ge13 shifts the Seeebeck coefficient to positive values. The Yb3Co4Sn13 has a maximal ZT parameter…
Half-Heusler compounds usually exhibit relatively higher lattice thermal conductivity that is undesirable for thermoelectric applications. Here we demonstrate by first-principles calculations and Boltzmann transport theory that the BiBaK system is an exception, which has rather low thermal conductivity as evidenced by very small phonon group velocity and relaxation time. Detailed analysis indicates that the heavy Bi and Ba atoms form a cage-like structure, inside which the light K atom rattles with larger atomic displacement parameters. In combination with its good electronic transport propert…
We have investigated the systematic transport properties of the layered 112-type cobaltite LaBaCo2O5.5 by means of electrical resistivity, magnetoresistance, electroresistance and thermoelectric measurements in various conditions. In order to understand the complex conduction mechanism of LaBaCo2O5.5, the transport data have been analyzed using different theoretical models. The system shows semiconductor-semiconductor like transition (TSC) around 326K, corresponding to ferromagnetic transition and in the low temperature region resistivity data follows the Motts variable range hopping model. In…
Polycrystalline sample of the new layered superconductor Bi4O4S3 is successfully synthesized by solid-state reaction method by using Bi, S and Bi2O3 powders with one step reaction. The superconducting transition temperature (Tconset=4.5 K), the zero resistance transition temperature (Tc0=4.07 K) and the diamagnetic transition temperature (4.02 K at H=10 Oe) were confirmed by electrical transport and magnetic measurements. Also, our results indicate a typical type II-superconductor behavior. In addition, a large thermoelectric effect was observed with a dimensionless thermoelectric figure of me…
High-throughput calculations are a very promising tool for screening a large number of compounds in order to discover new useful materials. Ternary intermetallic are thus investigated in the present work to find new compounds potentially interesting for thermoelectric applications. The screening of the stable non-metallic compounds required for such applications is obtained by calculating their electronic structure by DFT methods. In a first part, the study of the density of states at the Fermi level of well-known chemical elements and binary compounds allows to empirically optimize the select…
The discovery of Heusler alloys has revolutionized the research field of intermetallics due to the ease with which one can derive potential candidates for multifunctional applications. During recent years, many half Heusler alloys have been investigated for their thermoelectric properties. The f electron based rare earth ternary half Heusler compound DyPdBi has its f energy levels located close to the Fermi energy level. Other research efforts have emphasized that such materials have good thermoelectric capabilities. We have explored using first principles the electronic band structure of DyPd…
The copper silver selenide has two phases: the low-temperature semimetal phase (α-CuAgSe) and high-temperature phonon-glass superionic phase (\b{eta}-CuAgSe). In this work, the electric transport and thermoelectric properties of the two phases are investigated. It is revealed that the \b{eta}-CuAgSe is a p-type semiconductor and exhibits low thermal conductivity while the α-CuAgSe shows metallic conduction with dominant n-type carriers and low electrical resistivity. The thermoelectric figure of merit zT of the polycrystalline \b{eta}-CuAgSe at 623 K is ~0.95, suggesting that superionic CuAgSe…
We found that whisker crystals of Mo-doped Nb4SiTe4 show high thermoelectric performances at low temperatures, indicated by the largest power factor of 70 microW cm-1 K-2 at 230-300 K, much larger than those of Bi2Te3-based practical materials. This power factor is smaller than the maximum value in the 5d analogue Ta4SiTe4, but is comparable to that with a similar doping level. First principles calculation results suggest that the difference in thermoelectric performances between Nb and Ta compounds is caused by the much smaller band gap in Nb4SiTe4 than that in Ta4SiTe4, due to the weaker spi…
We have investigated the thermoelectric properties of the novel layered bismuth chalcogenides LaOBiS2-xSex. The partial substitution of S by Se produced the enhancement of electrical conductivity (metallic characteristics) in LaOBiS2-xSex. The power factor largely increased with increasing Se concentration. The highest power factor was 4.5 uW/cmK2 at around 470 deg. C for LaOBiS1.2Se0.8. The obtained dimensionless figure-of-merit (ZT) was 0.17 at around 470 deg. C in LaOBiS1.2Se0.8.
It is generally assumed in the thermoelectric community that the lattice thermal conductivity of a given material is independent of the electronic properties. This perspective is however questionable since the electron-phonon coupling could have certain effects on both the carrier and phonon transport, which in turn will affect the thermoelectric properties. Using SiGe compound as a prototypical example, we give an accurate prediction of the carrier relaxation time by considering scattering from all the phonon modes, as opposed to the simple deformation potential theory. It is found that the c…
Recently SnSe compound was reported to have a peak thermoelectric figure-5 of-merit (ZT) of 2.62 at 923 K, but the ZT values at temperatures below 750 K are relatively low. In this work, the electronic structures of SnSe are calculated using the density functional theory, and the electro- and thermo-transport properties upon varying chemical potential (or carrier density) are evaluated by the semi-classic Boltzmann transport theory, showing that the calculated ZT values along the a10 and c-axes below 675 K are in agreement with reported values, but that along the b-axis can be as high as 2.57 …
LaOBiPbS$_3$ is a kind of pnictogen-dichalcogenide layered compounds, which have recently been experimentally investigated as thermoelectric materials owing to their low thermal conductivity and high controllability of constituent elements. However, thermoelectric performance of LaOBiPbS$_3$ is at present not very high and that of its analogous compounds remains to be unknown. In this study, we theoretically investigate thermoelectric properties of 24 possible variations of the constituent elements in LaOBiPbS$_3$ from the viewpoint of the electronic structure. We find that some compounds can …
We explore the structural, electronic, mechanical and thermoelectric properties of a new half Heusler compound, HfPtPb which is all metallic heavy element and has been recently been proposed to be stable [Nature Chem 7 (2015) 308]. In the present work, we employ density functional theory and semiclassical Boltzmann transport equations with constant relaxation time approximation. The mechanical properties such as Shear modulus, Young modulus, elastic constants, Poisson ratio, and shear anisotropy factor are investigated. The elastic and phonon properties reveal that this compound is mechanicall…
Half-Heusler phases (space group F43m, C1b) have recently captured much attention as promising thermoelectric materials for heat-to-electric power conversion in the mid-to-high temperature range. The most studied ones are the RNiSn-type half-Heusler compounds, where R represents refractory metals Hf, Zr, and Ti. These compounds have shown a high-power factor and high-power density, as well as good material stability and scalability. Due to their high thermal conductivity, however, the dimensionless figure of merit (zT) of these materials has stagnated near 1 for a long time. Since 2013, the ve…
By using ab initio electronic structure calculations here we report the three new full Heusler alloys which are possessing very good thermoelectric behavior and expected to be synthesized in the laboratories. These are Fe2 ScP, Fe2 ScAs and Fe2 ScSb compound. First two compounds are indirect band gap semiconductors and the last one shows semimetallic ground state. The value of band gap of Fe2 ScP and Fe2 ScAs is 0.3 and 0.09 eV, respectively. These compounds show the presence of flat conduction bands along Γ - X-direction suggesting for the large electron like effective mass and promising for …
Determining defect types and concentrations remains a big challenge of semiconductor materials science. By using ab-initio thermal conductivity calculations we reveal that Ni/vacancy antisites, and not the previously claimed Sn/Zr antisites, are the dominant defects affecting thermal transport in half-Heusler compound ZrNiSn. Our calculations correctly predict the thermal conductivity dependence with temperature and concentration, in quantitative agreement with published experimental results. Furthermore, we find a characteristic proportionality between phonon-antisite scattering rates and the…
We investigate the thermoelectric properties of CaAl$_2$Si$_2$-type Zintl phase compounds $AB_2X_2$ ($A$ = Mg, Ca, Sr, Ba, $B$ = Mg, Zn, Cd, and $X$ = P, As, Sb) using first principles band calculations within the Boltzmann transport theory assuming the constant relaxation time approximation. We introduce the effective degree of valley degeneracy $n_{TE}$ to focus on the relationship between the thermoelectric properties and the multivalley character of the electronic band structure around the Fermi level. We also introduce a quantity $γ_{TE}$, which takes into account $n_{TE}$ and anisotropy …
Stacking-dependent thermoelectric transport in layered Sc_2Si_2Te_6 from first principles
Key Laboratory of Advanced Materials and Devices for Post-Moore Chips, Ministry of Education, University of Science and Technology Beijing（教育部先进后摩尔芯片器件重点实验室，北京科技大学）；School of Mathematics and Physics, University of Science and Technology Beijing（北京科技大学数理学院）
Half-Heusler compounds have emerged as promising thermoelectric materials that offer huge compositional space to tune their thermoelectric performance. A class of stable half Heusler compounds formed from elements of three specific groups in the periodic table viz. X$_{p}$X$'_{1-p}$Y$_{q}$Y$'_{1-q}$Z$_{r}$Z$'_{1-r}$ (with X, X$'$= Ti, Zr, Hf, Y, Y$'$ = Ni, Pd, Pt and Z, Z$'$ = Ge, Sn, Pb and p, q, r = 0, 0.25, 0.75 and 1) via various stoichiometric isoelectronic elemental substitution at the X, Y and Z sites respectively is investigated. Intelligent filters are employed at each step of our hig…
We present a study of the thermodynamic and physical properties of Tl5Te3, BiTl9Te6 and SbTl9Te6 compounds by means of density functional theory based calculations. The optimized lattice constants of the compounds are in good agreement with the experimental data. The electronic density of states and band structures are calculated to understand the bonding mechanism in the three compounds. The indirect band gap of BiTl9Te6 and SbTl9Te6 compounds are found to be equal to 0.256 eV and 0.374 eV, respectively. The spin-orbit coupling has important effects on the electronic structure of the two semi…
In the present work, we report the experimental thermopower ($α$) data for ZnV$_{2}$O$_{4}$ compound in the high temperature range 300-600 K. The value of $α$ is found to be $\sim$184 and $\sim$126 $μ$V/K at $\sim$300 and $\sim$600 K, respectively. The temperature dependent behavior of $α$ is almost linear in the measured temperature range. To understand the large and positive $α$ value observed in this compound, we have also investigated the electronic and thermoelectric properties by combining the \textit{ab-initio} electronic structures calculations with Boltzmann transport theory. Within t…
High-Tc Cu oxides consist of the alternating stack of the superconductive CuO2 layer and the block layer, such as Bi2Sr2O4 or La2-xSrxO2. By changing the block layer, we can change their physical properties, such as transition temperature Tc. The thermoelectric Co oxides have a similar layered structure composed of the conductive CoO2 layer and the blocking layer. Thus, we propose that their thremoelectric properties can be finely tuned by modifying the block layer.
A finite electronic band gap is a standard filter in high-throughput screening of materials using density functional theory (DFT). However, because of the systematic underestimation of band gaps in standard DFT approximations, a number of compounds may incorrectly be predicted metallic. In a more accurate treatment, such materials may instead appear as low band gap materials and could e.g. have good thermoelectric properties if suitable doping is feasible. To explore this possibility, we performed hybrid functional calculations on 1093 cubic materials listed in the MaterialsProjects database w…
We have performed a comprehensive set of first principles calculations to study the structural, elastic, electronic, magnetic and transport properties of new quaternary Heusler compounds CoZrMnX (X =Al, Ga, Ge, In). The results showed that all the quaternary Heusler compounds were stable in Type(I) structure. CoZrMnX are elastically stable and relatively hard materials. CoZrMnAl, CoZrMnGa, and CoZrMnIn are found to be ductile and CoZrMnGe is brittle in nature. The calculated Debye temperatures of all compounds are relatively high. The electronic structure calculations reveal that CoZrMnAl is n…
Current thermoelectric (TE) materials often have low performance or contain less abundant and/or toxic elements, thus limiting their large-scale applications. Therefore, new TE materials with high efficiency and low cost are strongly desirable. Here we demonstrate that, SiS and SiSe monolayers made from non-toxic and earth-abundant elements intrinsically have low thermal conductivities arising from their low-frequency optical phonon branches with large overlaps with acoustic phonon modes, which is similar to the state-of-the-art experimentally demonstrated material SnSe with a layered structur…
Half-Heusler (HH) alloys have attracted considerable interest as promising thermoelectric (TE) materials in the temperature range around 700 K and above, which is close to the temperature range of most industrial waste heat sources. The past few years have seen nanostructuing play an important role in significantly enhancing the TE performance of several HH alloys. In this article, we briefly review the recent progress and advances in these HH nanocomposites. We begin by presenting the structure of HH alloys and the different strategies that have been utilized for improving the TE properties o…
Type-I clathrate compounds have attracted a great deal of interest in connection with the search for efficient thermoelectric materials. These compounds constitute networked cages consisting of nano-scale tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the group 1 or 2 elements in the periodic table are encaged as the so-called rattling guest atom. It is remarkable that, though these compounds have crystalline cubic-structure, they exhibit glass-like phonon thermal conductivity over the whole temperature range depending on the states of rattling guest atoms in the tet…
In the present study, the structural, electronic, optical and thermoelectric properties of two isostructural chalcogenide materials, NaInS2 and NaInSe2 with hexagonal symmetry (R-3m) have been studied using the first principles method. A very good agreement has been found between our results with the available experimental and theoretical ones. The studied materials are semiconducting in nature as confirmed from the electronic band structure and optical properties.The strong hybridizations among s orbitals of Na, In and Se atoms push the bottom of the conduction band downward resulting in a na…
Identifying Highly Deformable van der Waals Layered Chalcogenides with Superior Thermoelectric Performance Using Deformability Factors and Interpretable Machine Learning
Layer-structured materials are often considered to be good candidates for thermoelectric materials, because they tend to exhibit intrinsically low thermal conductivity as a result of atomic interlayer interactions. The electrical properties of layer-structured materials can be easily tuned using various methods, such as band modification and intercalation. We report TiNBr, as a member of the layer-structured metal nitride halide system MNX (M = Ti, Zr, Hf; X = Cl, Br, I), and it exhibits an ultrahigh Seebeck coefficient of 2215 $μV/K$ at 300K. The value of the dimensionless figure of merit, ZT…
Perovskite compounds have the potential to harvest solar energy as well as exploit the thermoelectric potential of a number of available materials. Here, we present the electronic, structural, thermoelectric, and optical properties of Cs2AgSbX6 (X = Cl, Br, I) perovskite with the help of the density functional theory (DFT). The WC-GGA approximation was used to calculate the structural parameters. All these compounds crystalize in a cubic unit cell with lattice constant increasing from 10.65 Å (Cl) to 11.14 Å (Br) to 11.86 Å (I). The mBJ-functional shows a semiconducting nature for these compou…
We have explored the mechanical, electronic, optical and thermoelectric properties of p-type half-Heusler compound BaAgP for the first time using density functional theory based calculations. The mechanical and dynamical stability of this compound is confirmed by studying the Born stability criteria and phonon dispersion curve, respectively. It is soft, ductile and elastically anisotropic. The atomic bonding along a-axis is stronger than that along c-axis. The calculated electronic structure reveals that the studied compound is an indirect band gap semiconductor. The analysis of charge density…
Half-Heusler compounds (space group Fm3m) has garnered increasing attention in recent years in the thermoelectric community. Three decades ago, refractory RNiSn half-Heusler compounds (R represents refractory metals such as Hf, Zr, Ti) were found to be narrow-gap semiconductors with large Seebeck coefficients in 100s of micro-volt per Kelvin. Today, half-Heusler (HH) compounds have emerged as promising thermoelectric materials in the intermediate temperature range (400-800oC). HH materials are endowed with good thermal stability and scalability. Thermoelectric n-p modules based on HH materials…
Half Heusler (HH) thermoelectric alloys provide a wide platform to choose materials with non-toxic and earth abundant elements. This article presents an ab-initio theoretical evaluation of electrical and thermal transport properties of three Bismuth-based most promising thermoelectric alloys, selected out of 54 stable HH compounds. These are brand new compounds which are recently proposed to be stable (Nature Chem. 7, 308 (2015)) and may have interesting properties. The calculated band structure of the three compounds, namely HfRhBi, ZrIrBi and ZrRhBi, served as a hint for their promising ther…
In topological n-type thermoelectrics based on $Bi_{2}Te_{3}$ with atomic substitutions Bi $\rightarrow$ In, Te $\rightarrow$ Se, S, the morphology and the surface states of Dirac fermions on the interlayer (0001) surface of van der Waals were studied by scanning tunneling microscopy and spectroscopy (STM/STS) techniques. By the STM method, the dark and light spots on the surface were found, which intensities depend on the composition and thermoelectric properties of solid solutions. The observed surface morphology features in the solid solutions are explained by distortions of surface electro…
