Guangqian Ding

High-efficient thermoelectric materials: The case of orthorhombic IV-VI compounds.

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. Importantly, GeS, GeSe, and SnS exhibit comparative thermoelectric performance compared to SnSe. Especially, the Seebeck coefficients of GeS, GeSe, and SnS are even larger than that of SnSe under the studied carrier concentration and temperature region. We also use the Cahills model to estimate the lattice thermal conductivities at the room temperature. The large Seebeck coefficients, high power factors, and low thermal conductivities make these four orthorhombic IV-VI compounds promising candidates for high-efficient thermoelectric materials.

Examining the thermal conductivity of the half-Heusler alloy TiNiSn by first-principles calculations

The thermoelectric properties of the half-Heusler alloy TiNiSn have been studied for a decade, however, a theoretical report on its thermal conductivity is still relatively unknown, because it is difficult to effectively estimate the lattice thermal conductivity. In this work, we use the ShengBTE code developed recently to examine the lattice thermal conductivity of TiNiSn. The calculated lattice thermal conductivity at room temperature is 7.6 W m −1 K −1 , which is close to the experimental value of 8 W m −1 K −1 . We also find that the total and lattice thermal conductivities dependent on temperature are in good agreement with available experiments, and the total thermal conductivity is dominated by the lattice contribution. The present work is useful for the theoretical prediction of lattice thermal conductivity and the optimization of thermoelectric performance.

Thermoelectric properties of half-Heusler topological insulators MPtBi (M = Sc, Y, La) induced by strain

Thermoelectric (TE) materials and topological insulators (TIs) were recently known to exhibit close connection, which offers new prospects in improving the TE performance. However, currently known TE materials from TIs mostly belong to the early Bi2Te3 family. In order to extend TE materials to other classes of TIs, we use the first-principles combined with Boltzmann transport theory to study the electronic and TE properties of experimental half-Heusler compounds MPtBi (M = Sc, Y, La). We find that all MPtBi are topological semimetals at equilibrium lattices while TIs under a stretched uniaxial strain, which is in agreement with previous works. We further predict that comparable TE performance with Bi2Te3 can be realized in half-Heusler TI LaPtBi by an 8% stretched uniaxial strain. We also reveal that the lattice thermal conductivity of LaPtBi is unprecedented low compared with those of traditional half-Heusler compounds (not TIs). These findings indicate the potential of half-Heusler TIs as TE materials.

Band structure engineering of multiple band degeneracy for enhanced thermoelectric power factors in MTe and MSe (M = Pb, Sn, Ge)

The thermoelectric (TE) conversion efficiency is always limited by a low TE figure of merit (ZT). Improving ZT requires both a high power factor (PF) and a low thermal conductivity. So far, however, most efforts to improve ZT have been made by reducing the thermal conductivity rather than maximizing the PF. Recently, band engineering which can effectively solve the paradox between the density-of-states effective mass and carrier mobility, has been treated as an efficient approach to improve ZT by maximizing the PF. In this paper, based on first-principles and the Boltzmann transport theory, we calculate the electronic structure and thermoelectric properties of classical IV–VI semiconductors MTe and MSe (M = Pb, Sn, Ge). We find that band engineering of multiple band degeneracy induced by engineering the conduction bands near the Fermi level can increase the room temperature n-type PF around 3 to 8 times. The present work is useful in thermoelectrics and will attract more research interest in optimizing the TE performance by band engineering.

Multiple thermal spin transport performances of graphene nanoribbon heterojuction co-doped with Nitrogen and Boron

Graphene nanoribbon is a popular material in spintronics owing to its unique electronic properties. Here, we propose a novel spin caloritronics device based on zigzag graphene nanoribbon (ZGNR), which is a heterojunction consisting of a pure single-hydrogen-terminated ZGNR and one doped with nitrogen and boron. Using the density functional theory combined with the non-equilibrium Green’s function, we investigate the thermal spin transport properties of the heterojunction under different magnetic configurations only by a temperature gradient without an external gate or bias voltage. Our results indicate that thermally-induced spin polarized currents can be tuned by switching the magnetic configurations, resulting in a perfect thermal colossal magnetoresistance effect. The heterojunctions with different magnetic configurations exhibit a variety of excellent transport characteristics, including the spin-Seebeck effect, the spin-filtering effect, the temperature switching effect, the negative differential thermal resistance effect and the spin-Seebeck diode feature, which makes the heterojunction a promising candidate for high-efficiently multifunctional spin caloritronic applications.

Prediction of large magnetoelectric coupling in Fe4N/BaTiO3 and MnFe3N/BaTiO3 junctions from a first-principles study

The magnetoelectric (ME) effects of Fe4N/BaTiO3 and MnFe3N/BaTiO3 junctions are investigated using first-principles calculations. Compared with the very weak ME coupling effects for FeN/TiO2 interfaces in both Fe4N/BaTiO3 and MnFe3N/BaTiO3 junctions, the large ME coefficients are achieved at the more stable Fe2/TiO2 interface in the Fe4N/BaTiO3 junction and the more stable MnFe/TiO2 and Mn2/TiO2 interfaces in the MnFe3N/BaTiO3 junction. The magnetoelectric effect originates from the interface bonding mechanism which alters the chemical bonding and the hybridization at the interface when the electric polarization reverses. In addition, from the detailed analysis, we find that the interfacial FeII(MnII) (the face-centered sites Fe or Mn in Fe4N and MnFe3N) atom plays a more important role in the ME coupling than the interfacial FeI(MnI) (the corner sites Fe or Mn in Fe4N and MnFe3N) atom. These results suggest that Fe4N/BaTiO3 and MnFe3N/BaTiO3 junctions could be designed as multiferroic materials with large magnetoelectric coupling under their more stable interfaces. And the magnetic Mn-substitution doping at the interfacial FeII position in the Fe4N/BaTiO3 junction can possibly obtain a relatively large ME coefficient difference compared with doping at the interfacial FeI position.

Two-dimensional MoS2-MoSe2 lateral superlattice with minimized lattice thermal conductivity

Single-layer transition metal dichalcogenides (TMDCs) are showing promising thermoelectric applications due to their superior stability and electronic transport properties. Unfortunately, the intrinsic high lattice thermal conductivity prevents their further improvement of thermoelectric performance. Motivated by recent experimental synthesis of two-dimensional TMDC heterostructures and superlattices, we propose to minimize the lattice thermal conductivity of single-layer MoS2 and MoSe2 using the lateral superlattice (LS) as building blocks. First-principles calculations with the phonon Boltzmann transport equation reveal a remarkably low lattice thermal conductivity of MoS2-MoSe2 LS due to the enhanced anharmonic phonon scattering as compared to the individual single-layer. We also show that the strong phonon anisotropy of MoS2-MoSe2 LS is primarily ascribed to the out-of-plane quadratic acoustic branch and orientation-dependent anharmonic scattering. Our calculations clearly demonstrate the advantages of LS structure in minimizing the lattice thermal conductivity of single-layer TMDCs and also accelerate their related applications in the field of renewable energy.Single-layer transition metal dichalcogenides (TMDCs) are showing promising thermoelectric applications due to their superior stability and electronic transport properties. Unfortunately, the intrinsic high lattice thermal conductivity prevents their further improvement of thermoelectric performance. Motivated by recent experimental synthesis of two-dimensional TMDC heterostructures and superlattices, we propose to minimize the lattice thermal conductivity of single-layer MoS2 and MoSe2 using the lateral superlattice (LS) as building blocks. First-principles calculations with the phonon Boltzmann transport equation reveal a remarkably low lattice thermal conductivity of MoS2-MoSe2 LS due to the enhanced anharmonic phonon scattering as compared to the individual single-layer. We also show that the strong phonon anisotropy of MoS2-MoSe2 LS is primarily ascribed to the out-of-plane quadratic acoustic branch and orientation-dependent anharmonic scattering. Our calculations clearly demonstrate the advantages o...