Constant Scattering Time Approximation Research Articles

Modeling and simulation of multifaceted properties of X2NaIO6 (X = Ca and Sr) double perovskite oxides for advanced technological applications.

In this study, the authors have investigated the structural, optoelectronic, thermoelectric, and thermodynamic properties of Ca2NaIO6 and Sr2NaIO6 double perovskite oxides. Both materials exhibit semiconductor behavior with direct band gaps (Eg) of 0.353eV and 0.263eV, respectively. Optical parameters like absorption coefficient α(ω), reflectivity R(ω), dielectric constants, and refractive index have been calculated. The most notable absorption peaks are identified at 5.52eV (equal to 108.33 × 104cm-1) in the case of Ca2NaIO6 and at 11.16eV (equivalent to 118.17 × 104cm-1) for Sr2NaIO6. These findings suggest a promising outlook for applications in optoelectronics. Moreover, their commendably low thermal conductivity and a high figure of merit, particularly at low temperatures (100K), indicate their effectiveness as thermoelectric materials. This analysis underscores that these materials hold potential as suitable candidates for n-type doping, making them well-suited for use in thermoelectric devices. Studying thermal properties, including thermal expansion, bulk modulus, acoustic Debye temperature, entropy, and heat capacity, contributes to understanding the materials' thermodynamic stability. The titled materials are dynamically stable. The analysis of these double perovskite materials highlights their potential across various technological applications due to their advantageous structural, electronic, optical, and transport properties, offering new possibilities in material science and technology development. The study utilized the full potential linearized augmented plane wave (FP-LAPW) method in conjunction with density functional theory within the WIEN2k simulation code. This approach is widely recognized as one of the most dependable methods for evaluating the photovoltaic characteristics of semiconducting perovskites. The thermoelectric properties were ascertained using the rigid band approach and the constant scattering time approximation, both implemented in the BoltzTraP computational code.

Dirac dispersions, lattice dynamics and thermoelectric properties of quaternary Heusler alloys LiMgXY(X = Pt, Pd, Au; Y= Sb, Sn)

This manuscript reports the structural, mechanical, electronic, and thermoelectric properties of the LiMgYZ system Y = t, Pd, Au; Z = Sb, Sn) computed within the first-principle density functional theory combined with semi-classical Boltzmann transport equations. Comparing the relative energetic stability of type-I, type-II, and type-III atomic arrangement of basis atoms, the type-I arrangement is found to be the most stable among these. The lattice dynamics also confirm that the type-I phase is stable for all the studied alloys except LiMgAuSn. It is interesting to note that the electronic band structure of these materials exhibits the Dirac point. The temperature-dependent transport coefficients of these materials have been calculated within semi-classical Boltzmann transport formalism within constant scattering time approximation (CSTA). The number of states at the Fermi level has successfully depicted the behavior of electrical conductivity. Among all the studied alloys, LiMgPtSb shows the highest temperature coefficient of resistivity which indicates that this material can be a good candidate for temperature sensing applications.

Spin-orbit coupling locked robust thermoelectric performance of SrTe: A comparison with CaTe

We have investigated the pressure dependence of structural, electronic and transport properties of cubic CaTe and SrTe using density functional theory. By employing semi-classical Boltzmann-transport-formalism their transport properties are computed within constant scattering time approximation. Without spin–orbit-coupling (SOC), one finds multiple Dirac points along various directions around the M point in the Brillouin zone. SOC opens up gaps at all points except one Dirac point along the M-R direction. We have also explored the effect of isotropic compressive strain on thermoelectric properties. The effect of SOC is prominent for SrTe results into enhanced electrical conductivity by 20 times and power factor by almost 25 times. Doping of charge carriers results in improvedZT of CaTe. However, in SrTe only electron type doping is beneficial for improving ZT. We find thatSrTe is robust 3D Dirac material with promising thermoelectric performance. Specifically, SOC results in robust thermoelectric properties against strain and temperature changes.

Thermoelectric and Piezoelectric Properties in Half-Heusler Compounds TaXSn (X = Co, Rh and Ir) Based on Ab Initio Calculations

In this paper, we report a theoretical study of the structural, electronic, thermoelectric and piezoelectric properties of TaXSn (X = Co, Rh and Ir) half-Heusler compounds crystallizing with cubic MgAgAs-type structure. We have made a quantitative evaluation of thermoelectric figure of merit (ZT) and the electromechanical coupling coefficient (k14) of these compounds. Accordingly, we intend to combine the first-principles band structure calculations using (DFT)-based FP-LAPW approach and the semi-classical Boltzmann transport theory within constant scattering time approximation (CSTA) to interpret and predict the thermoelectric performance (ZTe) without the lattice thermal conductivity as a function of the chemical potential at various temperatures. Further, to obtain a reasonable estimate for (ZT) with the intrinsic lattice thermal conductivity, we have calculated the relaxation time (τ) at various temperatures using Bardeen–Shockley theory. Finally, for predicting piezoelectric coefficients, we have employed the modern theory of polarization as provided by density-functional perturbation theory (DFPT) based on plane waves and pseudo-potentials (PP-PW). Our key result is that these half-Heusler semiconductors are attractive for practical applications in energy-harvesting technology, which has a high (ZT) and (k14) of 0.89 and 0.25, respectively, at room temperature.

Electronic Structure and Transport Properties of La<sub>2</sub>Zr<sub>2</sub>O<sub>7</sub> Pyrochlore from First Principles

The first principle calculation as well as the Boltzmann transport calculation have been employed to study the high temperature electronic transport properties of pyrochlore La2Zr2O7. Combing constant scattering time approximation and experiment data, the electronic thermal conductivity and electron concentration are calculated as a function of temperature. The electronic thermal conductivity is 2.6×10-4 W/(m.s) at 1270K and 7.2×10-3 W/(m.s) at 1770K. The electron concentration increase rapidly with when the temperature is above 1600K.

Thermoelectric properties of n-type SrTiO3

We present an investigation of the thermoelectric properties of cubic perovskite SrTiO3. The results are derived from a combination of calculated transport functions obtained from Boltzmann transport theory in the constant scattering time approximation based on the electronic structure and existing experimental data for La-doped SrTiO3. The figure of merit ZT is modeled with respect to carrier concentration and temperature. The model predicts a relatively high ZT at optimized doping and suggests that the ZT value can reach 0.7 at T = 1400 K. Thus ZT can be improved from the current experimental values by carrier concentration optimization.

Interesting pressure dependence of power factor in BiTeI

We investigate pressure dependence of electronic structures and thermoelectric properties in BiTeI by using a modified Becke and Johnson exchange potential. Spin–orbit coupling (SOC) effects are also included due to giant Rashba splitting. Thermoelectric properties are illuminated through solving Boltzmann transport equations within the constant scattering time approximation. The calculated energy band gap of 0.36 eV agrees well with the experimental value of 0.38 eV. As the pressure increases, the energy band gap first decreases, and then increases. The Rashba energy has the opposite trend with the energy band gap. SOC has obvious detrimental influence on the power factor in both n-type and p-type doping. For low doping concentration, the power factor has the same trend with the energy band gap with increasing pressure, but shows a monotonic changing trend in high doping. It is found that the pressure can induce a significantly enhanced power factor in high n-type doping, which can be understood as pressure leading to two-dimensional-like density of states in the conduction bands. These results suggest that BiTeI may be a potential candidate for efficient thermoelectricity in n-type doping by pressure, turning an ordinary insulator into a topological insulator.

Electronic structure and thermoelectric properties of (Mg2X)2 / (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices from first-principle calculations

To identify thermoelectric materials containing abundant, low-cost and non-toxic elements, we have studied the electronic structures and thermoelectric properties of (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) superlattices with state-of-the-art first-principles calculations using a modified Becke and Johnson (mBJ) exchange potential. Our results show that (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 are semi-metals using mBJ plus spin-orbit coupling (mBJ + SOC), while (Mg2Si)2/ (Mg2Ge)2 is predicted to be a direct-gap semiconductor with a mBJ gap value of 0.46 eV and mBJ + SOC gap value of 0.44 eV. Thermoelectric properties are predicted by through solving the Boltzmann transport equations within the constant scattering time approximation. It is found that (Mg2Si)2/ (Mg2Ge)2 has a larger Seebeck coefficient and power factor than (Mg2Ge)2/ (Mg2Sn)2 and (Mg2Si)2/ (Mg2Sn)2 for both p-type and n-type doping. The detrimental influence of SOC on the power factor of p-type (Mg2X)2/ (Mg2Y)2 (X, Y = Si, Ge, Sn) is analyzed as a function of the carrier concentration, but there is a negligible SOC effect for n-type. These results can be explained by the influence of SOC on their valence and conduction bands near the Fermi level.

Band Structures and Transport Properties of Half-Heusler Compounds Nb<i>M</i>Sb (<i>M</i> = Fe, Ru)

The band structures and transport properties of Half-Heusler compounds NbFeSb and NbRuSb were studied using ab initio calculations and the Boltzmann transport equation with constant scattering time approximation (CSTA). Both compounds were identified as good p-type thermoelectric materials because of the combination of heavy and light bands in the valence band maximum (VBM). The Seebeck coefficients for NbRuSb were lower than that for NbFeSb; while the electrical conductivities for NbRuSb were little higher than that for NbFeSb. Consequently, the power factors in the p-type regimes for both compounds were similar at a given temperature. NbFeSb and NbRuSb could be efficient materials for thermoelectric generators based on the results in the present investigation.

Importance of spin–orbit coupling in power factor calculations for half-Heusler ANiB (A = Ti, Hf, Sc, Y; B[dbnd]Sn, Sb, Bi)

We investigate the spin–orbit coupling (SOC) effects on the electronic structures and semi-classic transport coefficients of half-Heusler ANiB (A = Ti, Hf, Sc, Y; BSn, Sb, Bi) by using generalized gradient approximation (GGA). Calculated results show that SOC splits the valence bands at high symmetry Γ point, and modifies the outline of Γ-centered valence bands, which has remarkable effects on the electron transport properties. Thermoelectric properties are performed through solving Boltzmann transport equations within the constant scattering time approximation. It is found that the compounds containing Sn atom have larger power factor in p-type doping than ones in n-type doping, and it is just the opposite for compounds containing Sb and Bi elements. The SOC has obvious detrimental influence on power factor in p-type doping, while has a negligible effect in n-type doping. These can be understood by considering the effects of SOC on the valence bands and conduction bands. The maximum power factors (MPF) are extracted in n-type and p-type doping with GGA and GGA + SOC, and the MPF at 300 K with SOC is predicted to be about 4.25%∼ 44.13% smaller than that without SOC in the case of p-type doping for ANiB (A = Ti, Hf, Sc, Y; BSn, Sb, Bi). Therefore, it is crucial to consider SOC effects for theoretical analysis in the case of p-type doping in half-Heusler compounds composed of heavy elements.

Electronic and thermoelectric properties of InN studied using ab initio density functional theory and Boltzmann transport calculations

The thermoelectric properties of indium nitride in the most stable wurtzite phase (w-InN) as a function of electron and hole concentrations and temperature were studied by solving the semiclassical Boltzmann transport equations in conjunction with ab initio electronic structure calculations, within Density Functional Theory. Based on maximally localized Wannier function basis set and the ab initio band energies, results for the Seebeck coefficient are presented and compared with available experimental data for n-type as well as p-type systems. Also, theoretical results for electric conductivity and power factor are presented. Most cases showed good agreement between the calculated properties and experimental data for w-InN unintentionally and p-type doped with magnesium. Our predictions for temperature and concentration dependences of electrical conductivity and power factor revealed a promising use of InN for intermediate and high temperature thermoelectric applications. The rigid band approach and constant scattering time approximation were utilized in the calculations.

Anisotropy and high thermopower of LaOBiS2

Transport properties of LaOBiS2 are studied using the Boltzmann theory in the constant scattering time approximation, the input to which are derived from the ab-initio calculations with spin–orbit interactions included. By virtue of the materials chemical bonding and band structure, strong anisotropy in the transport is observed, which also have non-symmetric behavior with respect to carrier type. With thermopower being in few hundreds μV/K, and LaO layers being charge inactive, it could be well anticipated that the thermal conductivity would be significantly suppressed along the crystallographic c-axis. We argue LaOBiS2 as a potential oxide thermoelectric material for high temperature applications. Further optimization of the materials properties in terms of “p” and “n” type conduction could also be accomplished via Sr and F doping, respectively, following the discovery of its isoelectronic counterpart SrFBiS2.

Electronic and thermoelectric properties of RuIn3−xAx(A=Sn,Zn)

Recently, we reported [M. Wagner et al., J. Mater. Res. 26, 1886 (2011)] transport measurements on the semiconducting intermetallic system RuIn3 and its substitution derivatives RuIn_{3-x}A_{x} (A = Sn, Zn). Higher values of the thermoelectric figure of merit (zT = 0.45) compared to the parent compound were achieved by chemical substitution. Here, using density functional theory based calculations, we report on the microscopic picture behind the measured phenomenon. We show in detail that the electronic structure of the substitution variants of the intermetallic system RuIn_{3-x}A_{x} (A = Sn, Zn) changes in a rigid-band like fashion. This behavior makes possible the fine tuning of the substitution concentration to take advantage of the sharp peak-like features in the density of states of the semiconducting parent compound. Trends in the transport properties calculated using the semi-classical Boltzmann transport equations within the constant scattering time approximation are in good agreement with the former experimental results for RuIn_{3-x}Sn_{x}. Based on the calculated thermopower for the p-doped systems, we reinvestigated the Zn-substituted derivative and obtained ZnO-free RuIn_{3-x}Zn_{x}. The new experimental results are consistent with the calculated trend in thermopower and yield large zT value of 0.8.