Electronic Contribution To Thermal Conductivity Research Articles

The thermoelectric properties of novel two-dimensional semiconductor ZrNBr alloyed with Fluorine: A DFT+U survey

In this survey, the thermoelectric properties of novel two-dimensional transition metal halide (ZrNBr) alloyed with Fluorine (F) in the replacement of Br atoms (with x = 0.5) have been studied. The density functional theory along with Hubbard’s potential has been used to study the density of states, the Seebeck coefficient, electrical conductivity, the electronic contribution of thermal conductivity, and the thermoelectric power factor. The dynamic and structural stability of the compounds has been proven by cohesive energy and phonon calculation results. By considering Hubbard’s potential of 3 eV the energy band gap of the electronic density of states has been enlarged to values of 2.73, and 2.7 eV for pure ZrNBr, and ZrNBr0.5F0.5, respectively. Moreover, the largest values of the thermoelectric power factor at room temperature (300 K) and without considering Hubbard’s potential were 29.12 × 1016 and 101 × 1016μW/m K2 s and at the negative chemical potential for pure ZrNBr, and ZrNBr0.5F0.5, respectively. While considering Hubbard’s potential, the largest peaks at 300 K were 26.42 × 1016μW/m K2 s (at positive chemical potential) and 41.41 × 1016μW/m K2 s (at negative chemical potential), for pure ZrNBr, and ZrNBr0.5F0.5, respectively. These values are in the ranges of the results for materials which are potential candidates for thermoelectric applications.

Transport properties of B and N sites vacancy defects graphene/h-BN heterostructures: First-principles study

First-principles calculations based on spin-polarized DFT-D2 approach have been carried out to study the transport properties of graphene/h-BN (G/h-BN) heterostructure (HS), 1 N vacancy defect in G/h-BN (G/h-BN_1 N), nearest neighbour of 1 N & 1B vacancy defects in G/h-BN (G/h-BN_nBN), and alternate zone of 1 N & 1B vacancy defects in G/h-BN (G/h-BN_aBN) materials. Transport properties like electrical conductivity (σ), electronic contribution of thermal conductivity (K), Seebeck coefficient (S) and thermoelectric power factor (P) are estimated through Boltzmann transport equations (BTE) within constant relaxation time approximation (RTA). Quantum ESPRESSO and BoltzTrap packages are used as a computational tool in the calculations. The considered materials are found to be stable van der Waals (vdWs) HS. The σ and K of graphene, h-BN, G/h-BN, G/h-BN_1 N, G/h-BN_nBN and G/h-BN_aBN are found to be increasing monotonically with temperature. The defected materials have slightly less value of σ than that of G/h-BN due to the effect of their effective mass and carrier concentration. At room temperature, K of G/h-BN, G/h-BN_nBN and G/h-BN_aBN retains similar value, while K of G/h-BN_1 N has increased slightly because the increase in Fermi velocity of electrons near Fermi level due to the reduction in effective mass thereby increasing the mean free path. We have analyzed the temperature dependent (constant value of energy) and energy dependent (constant value of temperature) S and P of above-mentioned materials, and found that S and P of defected HS are higher than that of non-defected HS materials due to combine dependence of n, T and m* on the value of S. The estimated S and P values of considered materials are consistent with reported value. Hence, they have budding employment in the thermoelectric devices.

Alloying of monolayer Zirconium Nitride with Magnesium and investigating its thermoelectric properties using DFT calculations

Thermoelectric materials include an extensive spectrum of solid-state compounds capable of converting thermal and electricity energies into each other. Due to their little harm to nature and their potential for fuel consumption reduction purposes, the thermoelectric materials have drawn great attentions in recent years. In this study, first-principle density functional theory (DFT) in conjunction with semi-classic Boltzmann transport theory is used to investigate the thermoelectric properties of Zirconium Nitride (ZrN) alloyed with different amounts of Magnesium. In order to show that the MgxZr1−xN alloy can act as a thermoelectric material its Seebeck coefficient, electrical conductivity, thermal conductivity, Hall coefficient, and thermoelectric power factor are studied. The Seebeck coefficient and electrical conductivity in the considered chemical potential and temperatures ranges have shown high values. In addition, it is found out that electronic contribution of thermal conductivity is one order of magnitude less in comparison with the other good thermoelectric materials.

Anisotropy of the thermal conductivity of bulk melt-cast Bi-2212 superconducting tubes

We investigate experimentally the anisotropy of the temperature dependence of the thermal conductivity of bulk Bi2Sr2CaCu2O8 (Bi-2212) cylinders fabricated by the melt-cast process. The thermal conductivity κ(T) along the axial and azimuthal directions are found to be equal within experimental uncertainty, while κ along the radial direction is found to be ∼40% larger than the other two. The results are in qualitative agreement with the weak partial texture of such tubes, corresponding also to an anisotropy of the resistivity ρ(T) above the critical temperature Tc. This resistivity anisotropy in the normal state is responsible for an anisotropy of the electronic contribution of thermal conductivity (Δκe), which is much smaller than the anisotropy Δκ of the total thermal conductivity. This indicates an anisotropic contribution of the phonons. The temperature dependence of the specific heat C(T) is also measured and shows that C(T)/T exhibits a well-defined maximum close to Tc. The combination of these experimental data can be used for assessing the thermal effects in bulk melt-cast Bi-2212, and underline the importance of taking the anisotropy of κ into account, e.g. for predicting the self-heating when the material is subjected to losses.

Effect of pressure on electronic and thermoelectric properties of magnesium silicide: A density functional theory study**Project supported by the Council of Scientific & Industrial Research (CSIR), India.

We study the effect of pressure on electronic and thermoelectric properties of Mg2Si using the density functional theory and Boltzmann transport equations. The variation of lattice constant, band gap, bulk modulus with pressure is also analyzed. Further, the thermoelectric properties (Seebeck coefficient, electrical conductivity, electronic thermal conductivity) have been studied as a function of temperature and pressure up to 1200 K. The results show that Mg2Si is an n-type semiconductor with a band gap of 0.21 eV. The negative value of the Seebeck coefficient at all pressures indicates that the conduction is due to electrons. With the increase in pressure, the Seebeck coefficient decreases and electrical conductivity increases. It is also seen that, there is practically no effect of pressure on the electronic contribution of thermal conductivity. The paper describes the calculation of the lattice thermal conductivity and figure of merit of Mg2Si at zero pressure. The maximum value of figure of merit is attained 1.83×10−3 at 1000 K. The obtained results are in good agreement with the available experimental and theoretical results.

Electronic and Thermoelectric Properties of Al doped Mg2Si Material: DFT Study

Magnesium Silicide and related alloys are very important for thermoelectric applications because of their non toxic nature, thermal stability, low density, relative abundance and low cost of production. In the present paper we have calculated electronic and thermoelectric properties of Al doped Mg2Si material (Mg2-xAlxSi, x=0.125, 0.25, 0.375) using Pseudo potential plane wave method based on DFT and Semi classical Boltzmann theory. Mg2Si semiconductor shows metallic nature when doped with Al atom and the conduction bands near Fermi level are composed of Si 3p, Mg 3s,3p and Al 3p. The calculations show ntype conduction, indicating that the electrical conduction is due to electron. The electrical conductivity increases with temperature; the negative value of Seebeck Coefficient also shows that the conduction is due to electron. The thermal conductivity increases slightly upon Al doping with increasing temperature due to the much larger contribution of lattice thermal conductivity over electronic thermal conductivity. In this paper we have calculated Seebeck coefficient, electrical conductivity and electronic contribution of thermal conductivity. The thermoelectric properties of doped system have been calculated in this temperature range 100K-1200K.

Polaron effects on the thermal conductivity of zigzag carbon nanotubes

Thermal conductivity of metallic zigzag carbon nanotube is investigated in the context of Holstein model. Green's function approach is implemented to calculate the electronic contribution of thermal conductivity as a function of radius of carbon nanotube, temperature and electron phonon coupling strength. Our results show that electronic thermal conductivity increases as a function of temperature at low temperature and gets a maximum value then decays at high temperature. Also the effect of radius of both metallic and semiconductor zigzag carbon nanotube on the thermal conductivity is studied. Our results show thermal conductivity increases when CNT diameter increases and decreases with electron phonon interaction strength.