The discovery of clathrate SrB3C3 under high pressure has inspired the exploration of new B-C clathrates. Here, we studied the structural evolution of a B-C framework over B and C contents in Sr(B,C)(10) at a pressure of 0-20 GPa using an unbiased structure search method in combination with first principles calculations. Analysis of the formation enthalpies and lattice dynamics suggest that a clathrate SrB8C2 and two 'tubular-like' SrB7C3 and SrB9C may be synthesized at 20 GPa and quenched to ambient pressure. All compounds have excellent mechanical properties with Vickers hardness reaching 23.6-32.1 GPa. The 'tubular-like' SrB7C3 and SrB9C are metals with their Fermi level crossing the bonding and antibonding states of B-p orbitals, respectively. However, unexpectedly, the clathrate SrB8C2 is a semiconductor with a direct bandgap of 0.3 eV and is fundamentally different from metallic SrB3C3. The calculated thermoelectric figure of merit ZT of SrB8C2 is 0.47, indicating that it is a potential thermoelectric material. The findings highlight the diversity of structures and physical properties of this new family of ternary B-C compounds.

Exploring high-performance thermoelectric materials with improved mechanical properties is important for broadening the application scope and the assembly requirement of stable devices. This work presents an effective strategy to discover hard thermoelectric material by inserting foreign atoms in the rigid covalent framework. We demonstrate this in boron-carbon clathrate Ⅶ structure, showing a promising candidate for highly efficient thermoelectric energy conversion, especially with Y atom filled in the cage, with a peak zT of 0.73 at 1, 000 K. The ab initio calculations indicate that YB3C3 system has low lattice thermal conductivity of 4.5 W/(m·K) at 1, 000 K due to the strong rattling of encaged Y atom. The strongly covalent framework provides highly degenerate band structures consisting of heavy and light electron pockets, which can maintain high carrier mobility arising from small effective mass and thus large group velocity. Consequently, high power factor can be achieved in YB3C3 for both electron and hole doping. In addition, it exhibits well mechanical properties and a Vickers hardness of 23.7 GPa because of the strong covalent boron-carbon framework. This work provides a novel avenue for the search of high-performance thermoelectric materials with excellent mechanical properties, based on boron-carbon clathrate structure.

Using particle swarm optimization and first-principles calculations, we discovered a novel high-pressure orthorhombic structure of CoP3 with the space group of Pnma, which is stable above 24.6 GPa. According to our calculations based on Boltzmann transport theory, the Seebeck coefficient of the Pnma phase is 6.5 times as great as that of the ambient Im-3 phase at a hole concentration of 1 x 1020 cm-3. The calculation further in-dicates the Pnma-CoP3 exhibits a maximal figure of merit ZT of 0.56 and 0.74 for p- and n-type at 800 K, respectively. Especially for p-type, the Pnma-CoP3 is quintuple better than the ambient phase which has a ZT of 0.1. The higher ZT value can be attributed to the deeper projected density of states generated by hybridization between P p states and Co d states near the Fermi level. Therefore, the high pressure mainly improves the ZT value by modulating electron properties. Current results demonstrate that the Pnma-CoP3 material is a competitive candidate for thermoelectric applications, especially under high temperature condition (800 K). This work provides a convenient alternative route to increase the thermoelectric performance of skutterudites.

Double-dome superconductivity in phosphorous-rich germanides was investigated by first-principles calculations. The results revealed a maximal Tc ∼ 20 K in newly predicted I4/m GeP4 at 120 GPa, attributed to the strong electron-phonon coupling.

Transition-metal sulfides, such as 1T- and 2H-TaS2, are attracting considerable interest in modern condensed matter physics for their diverse behaviors of the Mott state, peculiar charge-density-wave phase and superconductivity. The intrinsically low thermal conductivities along the cross-plane direction can advantage the potential high thermoelectric performance; yet, their insignificant power factors severely hampered the practical applications as thermoelectric devices. In this perspective, we herein present a new semiconducting phase in TaS3 with the space group C2/m predicted by the swarm-intelligence structure-searching method. The C2/m-TaS3 phase exhibits anisotropic multivalley band dispersions, which is beneficial for electronic transport. Meanwhile, the unique structure within nanopores leads to strong anharmonic scattering, significantly reducing the lattice thermal conductivity. As a result, the calculated figure of merit ZT can reach up to 1.68 and 1.57 at 800 K for p- and n-type, respectively that is comparable with conventional thermoelectric materials (e.g. PbTe, Bi2Te3). Therefore, our calculation reveals that the C2/m-TaS3 phase can be a potential high-performance candidate as non-toxic and eco-friendly thermoelectrics, and will stimulate further experimental exploration for understanding and tailoring thermoelectric capability in related transition-metal sulfides.

GeP3 materials are attracting broad research interest due to their typical puckered layer structure, high carrier mobility, and chemical stability. This peculiarity expedites the independent control of anisotropic electrical and thermal conductance, which is thus expected to possess great thermoelectric potential. Nevertheless, the metal characteristics of GeP3 in the bulk and thick films are adverse to real application because of the low Seebeck coefficient. Thus, it is highly desirable to explore effective solutions to broaden the band gap and also maintain its excellent electrical conductance. Herein, we designed the interlaced GeP3/hexagonal boron nitride (h-BN) bulk heterostructure using various component thicknesses. By using ab initio calculations based on the Boltzmann transport theory, we found that capping h-BN layer can obviously increase the band gap of the GeP3 layer by 0.24 eV, and more interestingly, the anisotropic electronic structure in the GeP3/h-BN heterostructure was accordingly modulated toward a favorable direction for high thermoelectricity. An ultrahigh ZT value of around 5 was predicted at 300 K in p-type GeP3/h-BN, attributed to the adjusted multivalley band structure. Overall, our work provided an effective route to design novel high-performance thermoelectrics through the appropriate construction of heterostructures.

Because of the unique layered structure, black phosphorus (BP) provides a possibility of relatively independent control in electrical and thermal conductivity for thermoelectrical applications. It is therefore of great interest to realize high-performance BP-based thermoelectrics as flexible non-toxic and ultralight devices in spite of the low energy conversion efficiency and structural instability of the bulk BP. In this work, we systematically study the thermoelectric properties for the two-dimensional BP from mono-layer up to quad-layer by first-principles calculations and Boltzmann transport theory. It can be concluded from the calculations that the thermoelectric performance of BP nanosheets can be effectively optimized by tuning the layer thickness. We reveal that the maximum ZT values at 300 and 500 K can reach up to 0.45 and 0.90 in p-type bi-layer BP along armchair direction, respectively, around 5 times higher than that of the bulk at room temperature. The high performance in bi-layer BP is mainly attributed to its highly anisotropic and degenerate carrier pockets. Accordingly, we further propose that the formation of BP/h-BN heterostructure can enhance ZT up to 1.2 at 500 K, which facilitates the real application of thin BP for flexible and eco-friendly thermoelectrics.

Lithium-rich phosphides have recently attracted considerable attention due to their potential application as high-capacity and high-rate anodes for lithium-ion batteries (LIBs). However, there is still short of the promising candidate thus far because of the poor electrical conductivity or huge volume change in the already known Li-P compounds. In this work, we report two novel Li-P states, Li5P2 and Li4P, stabilized under high pressures that are predicted to be quenchable down to ambient conditions by first-principles swarm structure calculations. The predicted P3m1 Li5P2 shows interesting features as a p-type semiconductor with an indirect band gap of 0.787 eV, possessing significant anisotropy properties in electrical transport, while R3[combining macron]m Li4P acts as a typical electride with metallic behavior at pressures of 0-82 GPa. More importantly, our calculations reveal that the theoretical capacities of Li5P2 and Li4P are predicted to reach 2164 and 3462 mA h g-1, respectively. Combined with the good electrical transport properties, the calculated volume expansion of Li5P2 (130%) is found to be much smaller than those of the previously reported Li-P compounds, indicating its potential as a high performance anode material for LIBs.

Clarifying how to design and fabricate an improved material composed by toxic-free and low-cost elements with high thermoelectric conversion efficiency represents one of the most challenging issues in modern materials science. In this work, we apply first-principles calculations and Boltzmann transport theory to study the electronic structure and transport properties on gamma-Cu2S materials. Our results show that a high thermoelectric figure of merit ZT of 1.2 can be achieved in hole-doped Cu2S crystal along b-axis direction at 500 K with an optimal doping of 4.1 x 10(19) CM-3. This high thermoelectric property originates from its remarkable valence band structure, which is highly anisotropic combining heavy and light features, and possesses five valence band maxima close to the Fermi level, leading to multivalley transport to enhance Seebeck coefficients and power factors. This work demonstrates hole-doped gamma-Cu2S is a promising eco-friendly thermoelectric material for largescale applications. Our exploration on the physical origin of the high thermoelectric efficiency in gamma-Cu2S can be helpful for further optimizing thermoelectric properties in experiments and sheds strong light on the search or even design of new thermoelectric materials through band engineering.

Black phosphorus (BP) has emerged as a promising thermoelectric candidate because of its strong electronic and thermal anisotropy, suggesting a large σ/κ ratio can be realized by controlling carrier transport orientation for a potentially high ZT. Nevertheless, to date, low conversion efficiency (ZT ≈0.08, 300 K) and poor stability of BP remain the major issues that have hampered its practical applications. This work reports a material family in simple composition XP7, XP3, and XP (X = N, As, Sb, Bi) with high‐performance thermoelectric properties by first‐principles calculations. Strikingly, an ultrahigh ZT up to 1.21 at 300 K is achieved in p‐type BiP7 with an optimal carrier concentration of 5.48 × 1019 cm−3 and ZT in n‐type NP3 can reach up to ≈0.87 at the electron concentration of 3.67 × 1019 cm−3 along the zigzag direction, owing to their enhanced density of states and multivalley band structures around the Fermi level through the resonant effects of VA guest and host atoms. Additionally, the calculations demonstrate further improvement in thermoelectric performance of pristine BP by ≈4.8 and 4.5 times at 800 K in p‐type NP and n‐type NP3, respectively. Considering the high stability, current results indicate that N–P based systems are highly promising for novel metal‐free, nontoxic, and ultralight thermoelectrics.