Abstract
A very active area of materials research is to devise methods that use machine learning to automatically extract predictive models from existing materials data. While prior examples have ...demonstrated successful models for some applications, many more applications exist where machine learning can make a strong impact. To enable faster development of machine-learning-based models for such applications, we have created a framework capable of being applied to a broad range of materials data. Our method works by using a chemically diverse list of attributes, which we demonstrate are suitable for describing a wide variety of properties, and a novel method for partitioning the data set into groups of similar materials to boost the predictive accuracy. In this manuscript, we demonstrate how this new method can be used to predict diverse properties of crystalline and amorphous materials, such as band gap energy and glass-forming ability.
The escalating and unpredictable cost of oil, the concentration of major oil resources in the hands of a few politically sensitive nations, and the long-term impact of CO
2
emissions on global ...climate constitute a major challenge for the 21
st
century. They also constitute a major incentive to harness alternative sources of energy and means of vehicle propulsion. Today's lithium-ion batteries, although suitable for small-scale devices, do not yet have sufficient energy or life for use in vehicles that would match the performance of internal combustion vehicles. Energy densities 2 and 5 times greater are required to meet the performance goals of a future generation of plug-in hybrid-electric vehicles (PHEVs) with a 40-80 mile all-electric range, and all-electric vehicles (EVs) with a 300-400 mile range, respectively. Major advances have been made in lithium-battery technology over the past two decades by the discovery of new materials and designs through intuitive approaches, experimental and predictive reasoning, and meticulous control of surface structures and chemical reactions. Further improvements in energy density of factors of two to three may yet be achievable for current day lithium-ion systems; factors of five or more may be possible for lithium-oxygen systems, ultimately leading to our ability to confine extremely high potential energy in a small volume without compromising safety, but only if daunting technological barriers can be overcome.
Confining extremely high potential energy in a small volume without compromising safety or lifetime is the grand challenge of lithium batteries.
Halide perovskites are anticipated to impact next generation high performance solar cells because of their extraordinary charge transport and optoelectronic properties. However, their thermal ...transport behavior has received limited attention. In this work, we studied the thermal transport and thermoelectric properties of the CsSnBr3‑xI x perovskites. We find a strong correlation between lattice dynamics and an ultralow thermal conductivity for series CsSnBr3‑xI x reaching 0.32 Wm–1K–1 at 550 K. The CsSnBr3‑xI x also possess a decent Seebeck coefficient and controllable electrical transport properties. The crystallography data and theoretical calculations suggest the Cs atom deviates from its ideal cuboctahedral geometry imposed by the perovskite cage and behaves as a heavy atom rattling oscillator. This off-center tendency of Cs, together with the distortion of SnX6 (X = Br or I) octahedra, produces a highly dynamic and disordered structure in CsSnBr3‑xI x , which gives rise to a very low Debye temperature and phonon velocity. Moreover, the low temperature heat capacity data suggests strong coupling between the low frequency optical phonons and heat carrying acoustical phonons. This induces strong phonon resonance scattering that induces the ultralow lattice thermal conductivity of CsSnBr3‑xI x .
We report a novel hierarchical microstructure in the PbSe-CdSe system, which collectively contributes to significant enhancement in thermoelectric performance, with
ZT
ave
∼ 0.83 across the 400-923 K ...temperature range, the highest reported for p-type, Te-free PbSe systems. We have investigated the local atomic structure as well as the microstructure of a series of PbSe-
x
CdSe materials, up to
x
= 10%. We find that the behavior of the Cd atoms in the octahedral rock salt sites is discordant and results in off-center displacement and distortion. Such off-centered Cd in the PbSe matrix creates (1) L-Σ electronic energy band convergence, (2) a flattened L band, both contributing to higher Seebeck coefficients, and (3) enhanced phonon scattering, which leads to lower thermal conductivity. These conclusions are supported by photoemission yield spectroscopy in air (PYSA), solid state
111
Cd,
77
Se NMR spectroscopy and DFT calculations. Above the solubility limit (>6%CdSe), we also observe endotaxial CdSe nano-precipitates with core-shell architecture formed in PbSe, whose size, distribution and structure gradually change with the Cd content. The nano-precipitates exhibit a zinc blende crystal structure and a tetrahedral shape with significant local strain, but are covered with a thin wurtzite layer along the precipitate/matrix interface, creating a core-shell structure embedded in PbSe. This newly discovered architecture causes a further reduction in lattice thermal conductivity. Moreover, potassium is found to be an effective p-type dopant in the PbSe-CdSe system, leading to an enhanced power factor, a maximum
ZT
of ∼1.4 at 923 K for Pb
0.98
K
0.02
Se-6%CdSe.
Off-centering and core-shell nanoscale CdSe precipitates lead to high thermoelectric performance for p-type, Te-free PbSe systems.
We use density functional theory to investigate the reaction between reduced CeO2–x (111) and water. H2O dissociation to hydroxyl is facile on surface vacancies and lattice oxygen, while subsequent ...decomposition of hydroxyl into H2 has a high barrier, which results in reversible adsorption of H2O under ultra-high-vacuum conditions. The barrier to H2 formation through hydroxyl decomposition decreases by 0.2 eV, while H2O formation becomes more difficult at high hydroxyl coverage. However, on isolated oxygen vacancies on a hydroxyl covered surface, H2 may be produced through a CeH intermediate with a 1.14 eV barrier. Oxygen vacancies are found to be more stable in the subsurface than in the surface layer at all vacancy coverages and for hydroxyl coverages less than 25–50%. The competition of H2O desorption and vacancy diffusion from the subsurface to the surface may prevent formation of hydroxyl from H2O dosing at low temperature, while the highly stable hydroxyl phase may provide a thermodynamic driving force for further surface reduction in the presence of water. On the basis of our calculations we suggest substitutional doping with a cation that binds H stronger than Ce may improve the decomposition of hydroxyls into hydrogen.
Crystalline semiconductors exhibiting innate low lattice thermal conductivity (κl) are technologically very important for the development of thermal barrier coatings, thermal data-storage devices, ...and high-performance thermoelectrics. Here, using first-principles calculations based on density functional theory and anharmonic lattice dynamics, we predict intrinsically low κl (<1 W/m K along the stacking direction for T ≥ 400 K) in many known layered semiconductors, AMM′Q3 (A = Na, K, Cs, Tl; M = Cu; M′ = Zr, Hf; Q = S, Se), that possess chemical bonding heterogeneity. We show that low κl in this class of materials arises from (a) the rattling vibrations of the weakly bonded A atoms, characterized by low-frequency localized phonon branches with very small dispersion that give rise to numerous additional scattering channels and (b) strong lattice anharmonicity which is manifested in the large-mode Gruneisen parameters that increase the phonon scattering rates. Our work uncovers inherent low κl in this previously unexplored class of metal chalcogenides which should open up opportunities for applications of these compounds in various thermal energy management devices.
With more than a hundred elements in the periodic table, a large number of potential new materials exist to address the technological and societal challenges we face today; however, without some ...guidance, searching through this vast combinatorial space is frustratingly slow and expensive, especially for materials strongly influenced by processing. We train a machine learning (ML) model on previously reported observations, parameters from physiochemical theories, and make it synthesis method-dependent to guide high-throughput (HiTp) experiments to find a new system of metallic glasses in the Co-V-Zr ternary. Experimental observations are in good agreement with the predictions of the model, but there are quantitative discrepancies in the precise compositions predicted. We use these discrepancies to retrain the ML model. The refined model has significantly improved accuracy not only for the Co-V-Zr system but also across all other available validation data. We then use the refined model to guide the discovery of metallic glasses in two additional previously unreported ternaries. Although our approach of iterative use of ML and HiTp experiments has guided us to rapid discovery of three new glass-forming systems, it has also provided us with a quantitatively accurate, synthesis method-sensitive predictor for metallic glasses that improves performance with use and thus promises to greatly accelerate discovery of many new metallic glasses. We believe that this discovery paradigm is applicable to a wider range of materials and should prove equally powerful for other materials and properties that are synthesis path-dependent and that current physiochemical theories find challenging to predict.
Thermoelectric materials enable direct conversion between thermal and electrical energy and provide a viable route for power generation and electric refrigeration. In this paper, we use ...first-principles based methods to predict a very high figure of merit (ZT) performance in hole doped GeSe crystals along the crystallographic b-axis, with maximum ZT ranging from 0.8 at 300 K to 2.5 at 800 K. This extremely high thermoelectric performance is due to a threefold synergy of properties in this material: (1) the exceptionally low lattice thermal conductivity in GeSe due to anharmonicity of vibrational modes, (2) the increased electrical conductivity due to hole doping and increased carrier concentration, and (3) an enhanced Seebeck coefficient via a multiband effect induced by hole doping. The predicted ZT results of hole-doped GeSe are higher than that of hole doped SnSe, which we have recently reported as having experimentally observed record-breaking thermoelectric efficiency. The overall ZT of hole doped GeSe crystals outperforms all current state-of-the-art thermoelectric materials, and this work provides an urgent computational materials prediction that is in need of experimental testing.
Ultrathin conformal coatings of the lithium ion conductor, lithium aluminum oxide (LiAlO2), were evaluated for their ability to improve the electrochemical stability of LiNi0.5Mn1.5O4/graphite Li-ion ...batteries. Electrochemical impedance spectroscopy confirmed the ion conducting character of the LiAlO2 films. Complementary simulations of the activation barriers in these layers match experimental results very well. LiAlO2 films were subsequently separately deposited onto LiNi0.5Mn1.5O4 and graphite electrodes. Increased electrochemical stability was observed, especially in the full cells, which was attributed to the role of the coatings as physical barriers against side reactions at the electrode–electrolyte interface. By comparing data from full cells where the coatings were applied to either electrode, the dominating failure mechanism was found to be the diffusion of transition metal ions from the cathode to the anode. The LiNi0.5Mn1.5O4/graphite full cell with less than 1 nm LiAlO2 on the positive electrode exhibited a discharge capacity of 92 mAh/g at C/3 rate. The chemical underpinnings of stable performance were revealed by soft X-ray absorption spectroscopy. First, both manganese and nickel were detected on the graphite electrode surfaces, and their oxidation states were determined as +2. Second, the ultrathin coatings on the anode alone were found to be sufficient to significantly reduce this deleterious process.
Thermoelectric (TE) materials convert heat energy directly into electricity, and introducing new materials with high conversion efficiency is a great challenge because of the rare combination of ...interdependent electrical and thermal transport properties required to be present in a single material. The TE efficiency is defined by the figure of merit ZT=(S2σ) T/κ, where S is the Seebeck coefficient, σ is the electrical conductivity, κ is the total thermal conductivity, and T is the absolute temperature. A new p‐type thermoelectric material, CsAg5Te3, is presented that exhibits ultralow lattice thermal conductivity (ca. 0.18 Wm−1 K−1) and a high figure of merit of about 1.5 at 727 K. The lattice thermal conductivity is the lowest among state‐of‐the‐art thermoelectrics; it is attributed to a previously unrecognized phonon scattering mechanism that involves the concerted rattling of a group of Ag ions that strongly raises the Grüneisen parameters of the material.
A p‐type thermoelectric material, CsAg5Te3, is presented. It exhibits ultralow thermal conductivity (ϰtol≈0.18 Wm−1 K−1) and a high figure of merit (ZT≈1.5 at 727 K). The low thermal conductivity is attributed to a previously unrecognized phonon scattering mechanism that involves the rattling of Ag ions, strongly raising the Grüneisen parameters of the material.
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