Theoretical Prediction of Thermoelectric Performance for Layered LaAgOX (X = S, Se) Materials in Consideration of the Four-Phonon and Multiple Carrier Scattering Processes.

Inspired by the experimental achievement of layered LaCuOX (X = S, Se) with superior thermoelectric (TE) performance, the TE properties of Ag-based isomorphic LaAgOX are systemically investigated by the first-principles calculation. The LaAgOS and LaAgOSe are direct semiconductors with wide bandgaps of ≈2.50 and ≈2.35 eV. Essential four-phonon and multiple carrier scattering mechanisms are considered in phonon and electronic transport calculations to improve the accuracy of the figure-of-merit (ZT). The p-type LaAgOX (X = S, Se) shows excellent TE performance on account of the large Seebeck coefficient originated from the band convergency and low thermal conductivity caused by the strong phonon-phonon scattering. Consequently, the optimal ZTs along the out-of-plane direction decrease in the order of n-type LaAgOSe (≈2.88) > p-type LaAgOSe (≈2.50) > p-type LaAgOS (≈2.42) > n-type LaAgOS (≈2.27) at 700 K, and the optimal ZTs of ≈1.16 and ≈1.29 are achieved for p-type LaAgOS and LaAgOSe at the same temperature. The present work would provide a deep insight into the phonon and electronic transport properties of LaAgOX (X = S, Se), but also could shed light on the way for the rational design of state-of-the-art heteroanionic materials for TE application.

Low-cost pentagonal NiX2 (X = S, Se, and Te) monolayers with strong anisotropy as potential thermoelectric materials.

Pentagonal compounds, as a new family of 2D materials, have recently been extensively studied in the fields of electrocatalysis, photovoltaics, and thermoelectrics. Encouraged by the successful synthesis of pentagonal PdSe2, the thermoelectric properties of low-cost pentagonal NiX2 (X = S, Se, and Te) monolayers are theoretically predicted with the help of first-principles calculations and the semiclassical Boltzmann transport theory. The high dynamic and thermal stabilities of pentagonal NiX2 (X = S, Se, and Te) monolayers are confirmed according to the phonon dispersion spectrums and ab initio molecular dynamics (AIMD) simulations. Indirect semiconductor features with wide bandgaps of 2.44, 2.31, and 1.88 eV at the Heyd-Scuseria-Ernzerhof (HSE06) level are discovered for pentagonal NiS2, NiSe2, and NiTe2 monolayers. Combining the Boltzmann transport equation and deformation potential theory, the Seebeck coefficient, power factor, and thermoelectric figure of merit (ZT) of NiX2 (X = S, Se, and Te) monolayers are evaluated from 300 to 600 K. The strongly anisotropic ZT values are discovered, which are attributed to the significant differences in electrical and thermal transport along the x and y directions. In addition, low lattice thermal conductivities are observed at 600 K for the pentagonal NiTe2 monolayer, accompanying higher ZT values of 1.81 and 1.58 along the x and y directions. The predicted thermoelectric properties indicate that the low-cost pentagonal NiSe2 and NiTe2 monolayers are potential anisotropic thermoelectric materials with high performance.