Search

Multi-objective machine learning (ML) methods are widely used in the field of materials because material optimizations are always multi-objective. Traditional multi-objective optimization methods mainly use a combination of hierarchical single-objective optimization. However, this strategy often has difficulty in finding features that can optimize multiple objectives simultaneously. In this work, taking the two objectives of ductility and thermoelectric performance as examples, interpretable and explainable ML strategies are used to find features that can simultaneously optimize multiple objectives. Specifically, SHAP and SISSO are applied for qualitative analysis and quantitative analysis between key features and target values. Both SISSO and SHAP show that EN(ab)A/Band Vare both positively correlated with zTand negatively correlated with Pugh’s ratio. Furthermore, domain knowledge helps to rationalize the two favorable features. The compounds with large EN(ab)A/Btend to have high band degeneracies, resulting in high zT. High EN(ab)A/Bcorrespond to weak B–X bonds, reducing the Gand Pugh's ratio, and improving the ductility of materials. On the other hand, large Vwill cause small G, which is beneficial to small Pugh’s ratio and large zT(vialow κL). The present work demonstrates the significance of multi-objective optimization and domain knowledge in the development of materials informatics.

GeTe exhibits excellent p-type medium-temperature thermoelectric properties with low toxicity and good mechanical characteristics, making it highly promising for development in the thermoelectric field. However, GeTe is prone to producing Ge vacancies, leading to high p-type carrier concentration, which results in elevated electronic thermal conductivity and a low Seebeck coefficient. This study systematically analyzes intrinsic and extrinsic defects in GeTe and its alloys, focusing on reducing p-type carrier concentration through first-principles calculations. The results reveal that substituting Ge-sites with Bi (BiGe) yields lower donor defect formation energy, effectively reducing p-type carrier concentration of GeTe and its alloys compared to other elemental doping. Additionally, alloying with certain elements, such as Pb, proves favorable for decreased p-type carrier concentration due to lowered energy levels of valence band maximum (VBM). Inspired by this, screening divalent elements for alloying on Ge-sites reveals that Sr, Ba, Eu, and Yb substantially reduce the VBM of GeTe. Further calculations for Ba and Yb-alloyed GeTe confirm changes in formation energies for donor (favorable) and acceptor (unfavorable) defects. Our work provides a systematic investigation of intrinsic and various extrinsic doping defects in GeTe and its alloys, shedding light on possible strategies of optimizing carrier concentration in these compounds.

The complex intrinsic defects of four ternary diamond-like ABX2(A: Cu/Ag; B: In; X: Te/Se) compounds are studied by first-principles calculations. The results show that Cu-based compounds are likely to generate acceptor VAdefect with p-type, while Ag-based compounds form donor BAwith n-type. The reasons are analyzed by the newly introduced density of energy (DOE).

Over the years, the fact that the quaternary diamond-like thermoelectric materials show much lower carrier mobilities than ternary compounds remains mysterious. In this work, by adopting first-principles defect chemistry and electrical transport calculations, the fundamental origin of the difference on carrier mobility between quaternary and ternary diamond-like compounds is addressed, exemplified by Cd2Cu3In3Te8. The results of defect chemistry show that the main intrinsic defects in quaternary compound Cd2Cu3In3Te8are substitutional defects, i.e., CdInand CdCu, differing from the copper vacancy defect in ternary Cu-based compound such as CuInTe2. The low defect formation energies in Cd2Cu3In3Te8result in high defect concentrations, which is caused by the similar atomic radii and electronegativities between CdIn and CdCu. Further calculations show that the low-energy defects are mainly located around the valence band maximum in Cd2Cu3In3Te8. The electrical transport calculations, considering both the acoustic phonon scattering and ionized impurity scattering, demonstrate that mainly due to the higher concentration of the ionized defects, the mobility of the quaternary Cd2Cu3In3Te8is much lower than that of ternary CuInTe2. Our work sheds light on the intrinsic defects in quaternary diamond-like compounds and their influence on charge transport.

By virtue of the excellent plasticity and tunable transport properties, Ag2S-based materials demonstrate an intriguing prospect for flexible or hetero-shaped thermoelectric applications. Among them, Ag2S1-xTexexhibits rich and interesting variations in crystal structure, mechanical and thermoelectric transport properties. However, Te alloying obviously introduces extremely large order-disorder distributions of cations and anions, leading to quite complicated crystal structures and thermoelectric properties. Detailed composition-structure-performance correlation of Ag2S1-xTexstill remains to be established. In this work, we designed and prepared a series of Ag2S1-xTex(x = 0–0.3) materials with low Te content. We discovered that the monoclinic-to-cubic phase transition occurs around x = 0.16 at room temperature. Te alloying plays a similar role as heating in facilitating this monoclinic-to-cubic phase transition, which is analyzed based on the thermodynamic principles. Compared with the monoclinic counterparts, the cubic-structured phases are more ductile and softer in mechanical properties. In addition, the cubic phases show a degenerately semiconducting behavior with higher thermoelectric performance. A maximum zT = 0.8 at 600 K and bending strain larger than 20% at room temperature were obtained in Ag2S0.7Te0.3. This work provides a useful guidance for designing Ag2S-based alloys with enhanced plasticity and high thermoelectric performance.

SrFBiS2is a quaternary n-type semiconductor with rock-salt-type BiS2and fluorite-type SrF layers alternately stacked along the caxis. The tunability of the crystal and electronic structures as well as the intrinsically low thermal conductivity make this compound a promising parent material for thermoelectric applications. In the current work, we show that alloying of Se and S in SrFBiS2reduces the optical band gap with the second conduction band serving as an electron-transport medium, simultaneously increasing the electron concentration and effective mass. In addition, the raw material Bi2Se3is shown to act as liquid adjuvant during the annealing process, favoring preferred-orientation grain growth and forming strengthen microstructural texturing in bulk samples after hot-pressed sintering. Highly ordered lamellar grains are stacked perpendicular to the pressure direction, leading to enhanced mobility along this direction. The synthetic effect results in a maximum power factor of 5.58 μW cm-1K-2at 523 K for SrFBiSSe and a peak zT= 0.34 at 773 K, enhancements of 180% compared with those of pristine SrFBiS2.

Lithium-rich antiperovskites are promising solid-state electrolytes for all-solid-state lithium-ion batteries because of their high structural tolerance and good formability. However, the experimentally reported proton-free Li3OCl is plagued by its inferior interfacial compatibility and harsh synthesis conditions. In contrast, Li2OHCl is a thermodynamically favored phases and is easier to achieve than Li3OCl. Due to the proton inside this material, it exhibits interesting lithium diffusion mechanisms. Herein, we present a systematic investigation of the ionic transport, phase stability, and electrochemical-chemical stability of Li2OHCl using first-principles calculations. Our results indicate that Li2OHCl is thermodynamically metastable and is an electronic insulator. The wide electrochemical stability window and high chemical stability of Li2OHCl against various electrodes are confirmed. The charged defects are the dominant conduction mechanism for Li-transport, with a low energy barrier of ∼0.50 eV. The Li-ion conductivity estimated by ab initiomolecular dynamics simulations is about 1.3×10-4S cm-1at room temperature. This work identifies the origin of the high interfacial stability and ionic conductivity of Li2OHCl, which can further lead to the design of such as a cathode coating. Moreover, all computational methods for calculating the properties of Li2OHCl are general and can guide the design of high-performance solid-state electrolytes.