Strong quartic anharmonicity, ultralow thermal conductivity, high band degeneracy and good thermoelectric performance in Na2TlSb

GeTe Thermoelectrics

Thermoelectric materials with crystal-amorphicity duality induced by large atomic size mismatch

Extraordinary thermoelectric performance in MgAgSb alloy with ultralow thermal conductivity

Ultralow thermal conductivity and high thermoelectric performance induced by dimensionality reduction in chain-like compounds X2PtSe2 (X=K, rb)

Antiperovskites are a burgeoning class of semiconducting materials that showcase remarkable optoelectronic properties and catalytic properties. However, there has been limited research on their thermoelectric properties. Combining first-principles calculations, self-consistent phonon theory and the Boltzmann transport equation, we have discovered that the hexagonal antiperovskites X(Ba & Sr)3BiN exhibit strong quartic lattice anharmonicity, where the anharmonic vibrations of the light N atoms primarily affect the lattice thermal conductivity (κL) along the c-axis direction. As a result, the lattice thermal conductivities along the a(b)-axis direction are low. At 300 K, the κL values of Ba3BiN and Sr3BiN are only 1.27 W m-1 K-1 and 2.24 W m-1 K-1, respectively. Moreover, near the valence band maximum, the orbitals of the N atoms dominate. This dominance allows Sr3BiN to achieve high power factor under p-type doping, resulting in an impressive thermoelectric figure of merit (ZT) of 0.94 along the c-axis direction at 800 K. In the a(b)-axis direction, at 800 K, n-type doped Ba3BiN exhibits a ZT value of 1.47, surpassing that of traditional thermoelectric materials. Our research elucidates that the hexagonal antiperovskites X(Ba & Sr)3BiN represent a category of potential thermoelectric materials with pronounced anisotropy, low thermal conductivity, and high thermoelectric performance.

Extremely strong four-phonon scattering and ultra-low lattice thermal conductivity due to quartic anharmonicity in fluoride perovskites XHgF3 (X = K, Rb)

The filled tetrahedral compound NaZnP with strong quartic anharmonicity and good thermoelectric properties

Room temperature high thermoelectric performance of Bi-based full-Heusler compounds CsxRb[formula omitted]Bi with strong anharmonicity

The search for non-toxic and low-cost perovskites with high thermoelectric performance is still a challenge despite low thermal conductivity. The thermoelectric properties of nitride anti-perovskites X3BN (B = Bi, Sb, X = Mg, Ca, Sr) with a cubic structure were investigated using density functional theory and machine learning interatomic potential. The low Debye temperature and thermal conductivity were obtained due to strong lattice anharmonicity, and the phonon vibration modes were also analyzed. The high band degeneracy and suitable bandgap lead to a large power factor. The maximum power factor is 7.54 mW/mk2 for Mg3BiN at 900 K. We obtained a maximum ZT of 1.49 for p-type Sr3BiN, and it is 1.22 for n-type doping at 900 K. The ZT for Mg3BiN is 1.18 and 1.19 for p-type and n-type doping, respectively. Our calculations reveal that these anti-perovskites are excellent materials for non-toxic and low-cost thermoelectric applications.

The elastic and thermoelectric properties of Ca5Al2Sb6 under pressure are studied using ab initio calculation and semiclassical Boltzmann theory. The calculated elastic constants and minimum thermal conductivity indicate that Ca5Al2Sb6 exhibits an anisotropic structure and high thermoelectric performance. The size of the band gap shows a nonlinear change with increasing pressure. Based on the electronic structure, the calculated thermoelectric parameters show that the Seebeck coefficient has no obvious change under pressure, whereas the electrical conductivity improves with increasing pressure. Therefore, the power factor increases at an appropriate pressure of P = 2.6 GPa. P-type doping of Ca5Al2Sb6 may achieve better thermoelectric performance than n-type doping, in agreement with experiment. The anisotropic thermoelectric properties of Ca5Al2Sb6 indicate that the thermoelectric performance along the z-direction is superior to other directions. This is attributed to the combination of the large dispersion and high band degeneracy along the Γ-Z direction in the band structure.

Copper sulfides have attracted great attention recently in the thermoelectric community due to the liquid-like behavior of Cu ions. Among the numerous copper sulfides, digenite Cu1.80S has a poorer thermoelectric performance but better stability than the state-of-the-art binary copper sulfide Cu1.97S. In this study, good stability and high thermoelectric performance were simultaneously obtained in Fe-doped Cu1.80S. Because Fe ions will not form a concentration gradient under an external field to change the critical voltage, Fe-doped Cu1.80S samples inherit the good stability of the pristine Cu1.80S. The critical voltage for Cu1.80Fe0.064S is 0.16 V at 750 K, which has been the largest value reported so far. Likewise, the Fe dopants can significantly improve the thermoelectric performance by suppressing the too high electrical conductivity of Cu1.80S. The peak dimensionless figure of merit (zT) for Cu1.80Fe0.064S is around 0.8 at 750 K, about four times that of Cu1.80S. The average zT for Cu1.80Fe0.064S is 0.40 in 300-750 K, which is amongst the highest values in reported thermoelectric sulfides. Combining the good stability and high thermoelectric performance, the present Cu1.80Fe0.064S has great potential to be used in the application of waste heat harvesting in the middle temperature range.

Nanostructured PEDOT-based multilayer thin films with high thermoelectric performances

Thermal conductivity and power factor are key factors in evaluating heat transfer performance and designing thermoelectric conversion devices. To search for materials with ultralow thermal conductivity and a high power factor, we proposed a set of universal statistical interaction descriptors (SIDs) and developed accurate machine learning models for the prediction of thermoelectric properties. For lattice thermal conductivity prediction, the SID-based model achieved the state-of-the-art results with an average absolute error of 1.76W m-1 K-1. The well-performing models predicted that hypervalent triiodides XI3 (X = Rb, Cs) have ultralow thermal conductivities and high power factors. Combining first-principles calculations, the self-consistent phonon theory, and the Boltzmann transport equation, we obtained the anharmonic lattice thermal conductivities of 0.10 and 0.13W m-1 K-1 for CsI3 and RbI3 in the c-axis direction at 300K, respectively. Further studies show that the ultralow thermal conductivity of XI3 arises from the competition of vibrations between alkali metal atoms and halogen atoms. In addition, at 700K, the thermoelectric figure of merit ZT values of CsI3 and RbI3 are 4.10 and 1.52, respectively, at the optimal hole doping level, which indicates hypervalent triiodides are potential high performance thermoelectric materials.

High thermoelectric performance in multiscale Ag8SnSe6 included n-type bismuth telluride for cooling application

The core effects of high entropy alloys distinguish high entropy alloying from ordinary multielement doping, allowing for a synergy of band structure and microstructure engineering. Here, a systematic synthesis, structural, theoretical, and thermoelectric study of multi‐principal‐element‐alloyed SnTe is reported. Toward high thermoelectric performance, the entropy of mixing needs to be high enough to make good use of the core effects, yet low enough to minimize the degradation of carrier mobility. It is demonstrated that high entropy of mixing extends the solubility limit of Mn while retaining the lattice symmetry, the enhanced Mn content elicits multiscale microstructures. The resulting ultralow lattice thermal conductivity of ≈0.32 W m−1 K−1 at 900 K in (Sn0.7Ge0.2Pb0.1)0.75Mn0.275Te is not only lower than the amorphous limit of SnTe but also comparable to those thermoelectric materials with complex crystal structures and strong anharmonicity. Co‐alloying of (Sn,Ge,Pb,Mn) also enhances band convergence and band effective mass, yielding good power factors. Further tuning of the Sn excess yields a state‐of‐the‐art zT ≈1.42 at 900 K in (Sn0.74Ge0.2Pb0.1)0.75Mn0.275Te. In view of the simple face‐centered‐cubic structure of SnTe‐based alloys, these results attest to the efficacy of entropy engineering toward a new paradigm of high entropy thermoelecrics.