Thermoelectric Performance of the 2D Bi₂Si₂Te₆ Semiconductor

Abstract

Bi 2 Si 2 Te 6 , a 2D compound, is a direct band gap semiconductor with an optical band gap of ∼0.25 eV, and is a promising thermoelectric material. Single-phase Bi 2 Si 2 Te 6 is prepared by a scalable ball-milling and annealing process, and the highly densified polycrystalline samples are prepared by spark plasma sintering. Bi 2 Si 2 Te 6 shows a p-type semiconductor transport behavior and exhibits an intrinsically low lattice thermal conductivity of ∼0.48 W m −1 K −1 (cross-plane) at 573 K. The first-principles density functional theory calculations indicate that such low lattice thermal conductivity is derived from the interactions between acoustic phonons and low-lying optical phonons, local vibrations of Bi, the low Debye temperature, and strong anharmonicity result from the unique 2D crystal structure and metavalent bonding of Bi 2 Si 2 Te 6 . The Bi 2 Si 2 Te 6 exhibits an optimal figure of merit ZT of ∼0.51 at 623 K, which can be further enhanced by the substitution of Bi with Pb. Pb doping leads to a large increase in power factor S 2 σ, from ∼3.9 μW cm −1 K −2 of Bi 2 Si 2 Te 6 to ∼8.0 μW cm −1 K −2 of Bi 1.98 Pb 0.02 Si 2 Te 6 at 773 K, owing to the increase in carrier concentration. Moreover, Pb doping induces a further reduction in the lattice thermal conductivity to ∼0.38 W m −1 K −1 (cross-plane) at 623 K in Bi 1.98 Pb 0.02 Si 2 Te 6 , due to strengthened point defect (Pb Bi ′) scattering. The simultaneous optimization of the power factor and lattice thermal conductivity achieves a peak ZT of ∼0.90 at 723 K and a high average ZT of ∼0.66 at 400−773 K in Bi 1.98 Pb 0.02 Si 2 Te 6 .

Thermally conductive polymer-based composites: fundamentals, progress and flame retardancy/anti-electromagnetic interference design

“…The electrical conductivity, permeability and thickness of materials are three basic factors affecting the shielding effectiveness. 183 The electromagnetic shielding and heat dissipation that exist in highly integrated electronic devices can be well addressed by conductive polymer-based composites (CPCs). 208 MXenes with excellent metallic conductivity and interactions with polymers are favorable for electromagnetic wave shielding, which are called two-dimensional transition metal carbides and/or nitrides, 182,209–212 such as Ti 3 C 2 T x .…”

“…Composites with a uniform structure can be directly made by blending a conductor filler and an insulating resin and then processing and molding by opening mixing, internal mixing, injection molding and so on. Electrical conductors such as Fe, Cu, Au, and Ag are good anti-electromagnetic-interference and thermally conductive materials, and their thermal conductivity is determined by their electrons, phonons and electron-phonon coupling, [183][184][185] while their anti-electromagnetic-interference performance is determined by the reflection and absorption of electromagnetic waves caused by electron-electron interactions (i.e., Coulomb interactions) and electron-phonon interactions. 186,187 Therefore, these materials with high thermal and electrical conductivity show great application potential in anti-electromagnetic interference and thermal management fields.…”

“…4.2.1 Mechanism of anti-electromagnetic interference. The anti-electromagnetic-interference mechanism 183 is presented in Fig. 19.…”

“…The electrical conductivity, permeability and thickness of materials are three basic factors affecting the shielding effectiveness. 183 The attenuation value of electromagnetic waves is directly proportional to the electromagnetic shielding effectiveness. Shielding materials interact with electromagnetic fields through electrons and holes.…”

Improving thermoelectric performance by constructing a SnTe/ZnO core–shell structure

“…In the past few decades, intermediate temperature TE materials, such as Sb 2 Si 2 Te 6 , 7 Bi 2 Si 2 Te 6 , 8 GeTe, 9 AgMnSbTe 4 , 10 Mg 3 Sb 2 , 11 and SnSe, 12 have received widespread attention and undergone intensive research for their application prospects. For example, the well-investigated lead telluride (PbTe) based TE materials have obtained high ZT values, especially p-type PbTe.…”