DFT based study on structural stability and transport properties of Sr3AsN: A potential thermoelectric material

Antiperovskite materials are well known for their high thermoelectric performance and gained huge research interest. Here, we report the structural stability and transport properties of Sr$_3$AsN from a precise first-principles study. The calculated equilibrium lattice parameters are in a good agreement with the available data. We find that Sr$_3$AsN is a mechanically, energetically and dynamically stable at ambient condition. Our calculated electronic structure indicates that it is a direct bandgap semiconductor, with a value ~1.2 eV. Sr-4d and N-2p orbitals mainly formulate the direct bandgap. This antiperovskite possesses a high Seebeck coefficient. Although its lattice thermal conductivity is comparatively low, electronic thermal conductivity is very high. The calculated maximum TE figure of merit is 0.75 at 700 K, indicating that it is a potential material for thermoelectric applications.Comment: 22 pages, 11 figure

High Seebeck coefficient and ultra-low lattice thermal conductivity in Cs2InAgCl6

The elastic, electronic and thermoelectric properties of indium-based double-perovskite halide, Cs2InAgCl6 have been studied by first principles study. The Cs2InAgCl6 is found to be elastically stable, ductile, anisotropic and relatively low hard material. The calculated direct bandgap 3.67 eV by TB-mBJ functional fairly agrees with the experimentally measured value 3.3 eV but PBE functional underestimates the bandgap by 1.483 eV. The relaxation time and lattice thermal conductivity have been calculated by using relaxation time approximation (RTA) within the supercell approach. The lattice thermal conductivity (\k{appa}l) is quite low (0.2 Wm-1K-1). The quite low phonon group velocity in the large weighted phase space, and high anharmonicity (large phonon scattering) are responsible for small \k{appa}l. The room temperature Seebeck coefficient is 199 {\mu}VK-1. Such high Seebeck coefficient arises from the combination of the flat conduction band and large bandgap. We obtain power factors at 300K by using PBE and TB-mBJ potentials are ~29 and ~31 mWm-1K-2, respectively and the corresponding thermoelectric figure of merit of Cs2BiAgCl6 are 0.71 and 0.72. However, the maximum ZT value obtained at 700K is ~0.74 by TB-mBJ potential. The obtained results implies that Cs2InAgCl6 is a promising material for thermoelectric device applications.Comment: 19 pages. arXiv admin note: text overlap with arXiv:1801.0370

Extraordinary thermoelectric performance of ABaX compared to Bi2_2Te3_3

Thermoelectric materials can generate electricity directly utilizing heat and thus, they are considered to be eco-friendly energy resources. The thermoelectric efficiency at low temperatures is impractically small, except only a few bulk materials (Bi$_2$Te$_3$ and its alloys). Here, I predict two new thermoelectric materials, LiBaSb and NaBaBi, with excellent transport properties at low-medium temperature by using the first-principles method. The relatively low density of states near Fermi level, highly non-parabolic bands, and almost two times wider bandgap of NaBaBi lead to almost two times higher anisotropic power factor at 300K than that of Bi2Te3. On the other side, almost similar phonon density of states and anharmonicity of NaBaBi cause almost identical lattice thermal conductivity (but it is much higher in LiBaSb). These effects make it a superior thermoelectric material, with a predicted cross-plane (in-plane) ZT ~2 (~1) at 300 K for both n- and p-type carriers, even higher (~2.5 for p-type) at 350K. On the other hand, the isotropic maximum ZT of NaBaBi is ~1.2 and 1.6 at 350K for n and p-type carriers, respectively. However, LiBaSb is less suitable for low-temperature TE applications, because of its relatively wider bandgap and high lattice thermal conductivity

First-principles prediction of phonon-mediated superconductivity in XBC (X= Mg, Ca, Sr, Ba)

From first-principles calculations, we predict four new intercalated hexagonal $X$BC ($X$=Mg, Ca, Sr, Ba) compounds to be dynamically stable and phonon-mediated superconductors. These compounds form a LiBC like structure but are metallic. The calculated superconducting critical temperature, $T{_c}$, of MgBC is 51 K. The strong attractive interaction between $\sigma$-bonding electrons and the B${_{1g}}$ phonon mode gives rise to a larger electron-phonon coupling constant (1.135) and hence high $T_c$; notably, higher than that of MgB$_2$. The other compounds have a low superconducting critical temperature (4-17 K) due to the interaction between $\sigma$-bonding electrons and low energy phonons (E${_{2u}}$ modes). Due to their energetic and dynamic stability, we envisage that these compounds can be synthesized experimentally.Comment: 7 pages, 6 figure

Composite beam analogy fracture model (CBAFM) : a non-linear fracture mechanics model for concrete

The main objective of this dissertation is to develop a simple non-linear fracture mechanics model for the determination of fracture mechanics parameters for concrete, such as fracture process zone length (rp), critical fracture energy release rate (Gic), critical stress intensity factor (KO and fracture energy (GF). The fracture process zone (FPZ) is modeled as a damaged non-elastic cohesive band where the extent of damage due to microcracking varies from no damage at the boundary of FPZ to complete crack surface separation at the notch or macro-crack tip. The proposed method can predict theoretically both the pre-peak and post-peak load versus crack mouth opening displacement (P-CMOD) and load versus load point deflection (P-δ) behaviors for a three point bend (3-PB) single-edge notch (SEN) beam. To apply this method, one only needs to measure peak load (Pu) and corresponding crack mouth opening displacement (CMODu) of a 3-PB SEN beam, and cylinder compressive strength. This method does not require post-peak load-deflection or CMOD data. Furthermore, it does not require information as to the unloading characteristics of a beam. The testing machine need not be very stiff. This makes the testing procedure greatly simplified and makes it suitable not only for the testing laboratory but also for work sites where a closed-loop testing machine is not available. A microcomputer based simple numerical model is also developed based on the proposed fracture model. This model is verified by comparison with numerous experimental results as well as with other available methods from the literature

First-principles prediction of extraordinary thermoelectric efficiency in superionic Li2SnX3(X=S,Se)

Thermoelectric materials create an electric potential when subject to a temperature gradient and vice versa hence they can be used to harvest waste heat into electricity and in thermal management applications. However, finding highly efficient thermoelectrics with high figures of merit, zT$\geq$1, is very challenging because the combination of high power factor and low thermal conductivity is rare in materials. Here, we use first-principles methods to analyze the thermoelectric properties of Li$_2$Sn$X_3$ ($X$=S,Se), a recently synthesized class of lithium fast-ion conductors presenting high thermal stability. In p-type Li$_2$Sn$X_3$, we estimate highly flat electronic valence bands that render high Seebeck coefficients exceeding 400 ${\mu}$VK$^{-1}$ at 700K. In n-type Li$_2$Sn$X_3$, the electronic conduction bands are slightly dispersive however the accompanying weak electron-acoustic phonon scattering induces high electrical conductivity. The combination of high Seebeck coefficient and electrical conductivity gives rise to high power factors, reaching a maximum of 4 mWm$^{-1}$K$^{-2}$ in p-type Li$_2$SnS$_3$ and 8 mWm$^{-1}$K$^{-2}$ in n-type Li$_2$SnSe$_3$ at 300 K. Likewise, the thermal conductivity in Li$_2$Sn$X_3$ is low as compared to conventional thermoelectric materials, 2-5 Wm$^{-1}$K$^{-1}$ at room temperature. As a result, we estimate a maximum zT = 1.05 in p-type Li$_2$SnS$_3$ at 700 K and an extraordinary 3.07 (1.5) in n-type Li$_2$SnSe$_3$ at the same temperature (300 K). Our findings of huge zT in Li$_2$Sn$X_3$ suggest that lithium fast-ion conductors, typically employed as electrolytes in solid-state batteries, hold exceptional promise as thermoelectric materials.Comment: 21 Page

First-principles prediction of Structural Stability and Thermoelectric Properties of SrGaSnH

Thermoelectric materials based on earth-abundant and non-toxic elements are very useful in cost-effective and eco-friendly waste heat management systems. The constituents of SrGaSnH are earth-abundant and non-toxic, thus we have chosen SrSnGaH to study its structural stability and thermoelectric properties by using DFT, DFPT, and semi-classical Boltzmann transport theory. Our elastic and phonons calculations show that the compound has good structural stability. The electronic structure calculation discloses that it is an indirect bandgap (0.63 eV by mBJ+SOC) semiconductor. Light band hole effective mass leads to higher electrical conductivity along x-axis than that of along z-axis. On the other side, the weak phonon scattering leads to high lattice thermal conductivity ~10.5 W m-1K-1 at 300 K. Although the power factor (PF) is very high along the x-axis (above 10 mW m-1K-2 at 300 K), such large kl dramatically reduces ZT. The maximum values of in-plane and cross-plane ZT are ~1 (n-type), 0.8 (p-type) and 0.6 (n-type), (0.2 p-type) at 700 K, respectively. The present study has revealed that this compound has strong potential in eco-friendly TE applications