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This Methods/Protocols article is intended for materials scientists interested in performing machine learning-centered research. We cover broad guidelines and best practices regarding the obtaining...

In recent years, multi-phase materials capable of multi-ion transport have emerged as attractive candidates for a variety of electrochemical devices. Here, we provide experimental results for fabricating a composite electrolyte made up of a one-dimensional fast sodium-ion conductor, sodium zirconogallate, and an oxygen-ion conductor, yttria-stabilized zirconia. The composite is synthesized through a vapor phase conversion mechanism, and the kinetics of this process are discussed in detail. The samples are characterized using diffraction, electron microscopy, and electrochemical impedance spectroscopy techniques. Samples with a finer grain structure exhibit higher kinetic rates due to larger three-phase boundaries (TPBs) per unit area. The total conductivity is fitted to an Arrhenius type equation with activation energies ranging from 0.23 eV at temperatures below 550 ° C to 1.07 eV above 550 ° C . The electrochemical performance of multi-phase multi-species, mixed Na + and O 2 − conductor, is tested under both oxygen chemical potential gradient as well as sodium chemical potential gradient are discussed using the Goldman-Hodgkin-Kats (GHK) and the Nernst equation.

Mo2–xWxBC is suggested to be one of the only exceptionally high hardness, transition-metal-rich materials that also shows moderate ductility and compositional sustainability. This is demonstrated here through the synthesis of the Mo2–xWxBC (x = 1.1, 0.75, 0.5, 0.25, 0) solid solution and structural characterization using X-ray diffraction, electron microscopy, and density functional theory. All compounds crystallize in the orthorhombic space group, Cmcm, and follow Vegard’s law. Vickers microindentations show a decrease in hardness as tungsten is substituted by molybdenum owing to changes in the crystal chemistry and the loss of electron density. Calculating Pugh’s ratio based on the values derived from density functional perturbation theory reveals that these materials are surprisingly ductile throughout the solid solution, providing the potential to manipulate the hardness and ductility. Controlling this relationship is of great technological interest as most hard materials suffer from brittleness. More...

In this work comparative mechanical fatigue experiments were performed in order to quantify the mechanical stress delamination rates for both PVDF and PFA lining materials. Evidence was found for a Paris Law behavior when samples are cycled in blister test configurations. PFA liners exhibited crack growth constants C = 0.0486 c m / c y c l e and n = 0.9 while PVDF liners exhibited crack growth constants C = 0.0999 c m / c y c l e and n = 0.8 . Linear crack growth rates were observed which ranged from 0.042 ( ( a / a 0 ) / c y c l e ) at 3.10 bar up to 1.47 ( ( a / a 0 ) / c y c l e ) at 4.48 bar for PVDF and 0.024 ( ( a / a 0 ) / c y c l e ) at 2.59 bar up to 0.262 ( ( a / a 0 ) / c y c l e ) at 3.79 bar for PFA. PFA liners were found to fail at 5.52 bar while PVDF liners failed more violently at 6.21 bar. Overall fatigue ratings of the PVDF vs PFA linings should balance the faster delamination rates of PVDF liners vs the lower strength of PFA liners. It is unlikely that vessels with PVDF or PFA liners under fatigue failure due to vacuum-induced mechanical stresses since much larger stresses were required to cause low cycle fatigue failure. Instead, sample delamination is likely due to thermal stresses arising from a mismatch in thermal expansion between liner, fiber backing, epoxy, and metal substrate.

One and two pseudo-reference electrode proton exchange membrane fuel cell devices were fabricated using composite thin film composed of Nafion and Ag paste as the reference electrode. Three and four-electrode electrochemical studies were performed isolating different parts of the cell. Summing the scans utilizing the reference electrode(s) resulted in good agreement with the two-electrode scan across the entire cell. A DC current was passed through the cell under constant resistive load conditions. The equations necessary to determine the cell and the anode/cathode-reference impedance under constant resistive load are presented. A high frequency depressed arc present in the spectra of the entire cell had contributions from both the anode-reference and the cathode-reference scans. Reactance present in the four-electrode measurements isolating a section of the membrane further suggests that the high frequency depressed semicircle in the cell scan can, at least in part, be attributed to the membrane. The present work shows that by using embedded pseudo-reference electrodes, the polarization behavior of cathode and anode can be investigated independently and unambiguously without the need for de-convolution of spectra across the entire cell.

An ideal proppant for hydraulic fracturing should be neutrally buoyant, implying a very low bulk specific gravity, while maintaining crush resistance and low acid solubility. To this end, an iron oxide and kaolinite based proppant has been developed. In this work, synthesis conditions are explored by varying partial pressures of oxygen from 1.772 × 10 –13 atm to 1.821 × 10 –11 atm. The Fe 2 O 3 reduces to FeO and reacts with kaolinite decomposed to mullite to form Fe 2 SiO 4 , FeSiO 3 , and FeAl 2 O 4 . As a result, the proppant develops large pores (~100 µm), giving it a low bulk density (1.43 g/cm 3 ), and high porosity (45.2 vol%) at P O 2 of 1.821 × 10 –11 atm. The proppant sintered at P O 2 of 1.772 × 10 –13 atm is characterized by smaller pores (26 µm), higher density (1.72 g/cm 3 ) and lower porosity (37.5 vol%). Crush resistance testing at 9000 psi yields 6.8 wt% fine particles increasing to 17.7 wt% in porous samples. Acid solubility varies from 5.5 wt% loss increasing to 12.9 wt% in porous samples. A wide variety of microstructures with associated mechanical and chemical features are possible when composition, partial pressure of oxygen and temperature are varied during sintering.

Predicting crystal structure has always been a challenging problem for physical sciences. Recently, computational methods have been built to predict crystal structure with success but have been limited in scope and computational time. In this paper, we review computational methods such as density functional theory and machine learning methods used to predict crystal structure. We also explored the breadth versus accuracy of building a model to predict across any crystal structure using machine learning. We extracted 24 913 unique chemical formulas existing between 290 and 310 K from the Pearson Crystal Database. Of these 24 913 formulas, there exists 10 711 unique crystal structures referred to as entry prototypes. Common entries might have hundreds of chemical compositions, while the vast majority of entry prototypes is represented by fewer than ten unique compositions. To include all data in our predictions, entry prototypes that lacked a minimum number of representatives were relabeled as “Other”. By s...

We report the growth of p -type As-doped, Cd-rich CdTe single crystals using metallic Cd as the solvent in the traveling-heater method. We investigate the growth process from Cd solution in terms of the solid-liquid interface shape and the effects of As incorporation on p -type doping. The resulting CdTe crystals have Cd-rich composition which enhances p -type doping. The As doping efficacy was measured for As concentrations by the combination of inductively coupled plasma mass spectrometry, capacitance-voltage measurements. The p -type doping concentration varied from 6 × 10 15 to 8 × 10 16 cm −3 with increasing As concentration, with an apparent doping limit just below 10 17 cm −3 .

Roadway marking visibility has made substantial improvements since the beginning of the 20th century. The most common solution for increasing the visibility of road markings is the use of retroreflective beads, which suffer from decreased performance under wet conditions. To remedy this, alternative road marking visibility techniques such as luminescent paint have been investigated. A promising new technology involves the use of phosphors such as strontium aluminate doped with europium and dysprosium ions (SrAl2O4:Eu2+,Dy3+). This technology shows potential to be seen throughout the night. The two hurdles blocking the path for the use of phosphors in road marking paint are the need to stabilize the particles in the paint matrix, and the tendency of the phosphor to hydrolyze. In this review, an explanation of the science behind stabilization is set forth alongside several methods that show potential for mitigating hydrolysis.

A machine-learning model has been trained to discover Heusler compounds, which are intermetallics exhibiting diverse physical properties attractive for applications in thermoelectric and spintronic materials. Improving these properties requires knowledge of crystal structures, which occur in three subtle variations (Heusler, inverse Heusler, and CsCl-type structures) that are difficult, and at times impossible, to distinguish by diffraction techniques. Compared to alternative approaches, this Heusler discovery engine performs exceptionally well, making fast and reliable predictions of the occurrence of Heusler vs non-Heusler compounds for an arbitrary combination of elements with no structural input on over 400 000 candidates. The model has a true positive rate of 0.94 (and false positive rate of 0.01). It is also valuable for data sanitizing, by flagging questionable entries in crystallographic databases. It was applied to screen candidates with the formula AB$_{2}$C and predict the existence of 12 novel gallides MRu$_{2}$Ga and RuM$_{2}$Ga (M = Ti-Co) as Heusler compounds, which were confirmed experimentally. One member, TiRu$_{2}$Ga, exhibited diagnostic superstructure peaks that confirm the adoption of an ordered Heusler as opposed to a disordered CsCl-type structure.

PbPdO2 is a band semiconductor with a band gap arising from the filled d8 nature of square-planar Pd2+. We establish that hole doping through Li substitution for Pd in PbPdO2 results in a p-type metallic oxide with a positive temperature coefficient of resistance for substitution amounts as small as 2 mol % Li for Pd. Furthermore, PbPd1–xLixO2 demonstrates a high Seebeck coefficient and is therefore an oxide thermoelectric material with high thermopower despite the metallic conductivity. Up to 4 mol % Li is found to substitute for Pd as verified by Rietveld refinement of neutron diffraction data. At this maximal Li substitution, the resistivity is driven below the Mott metallic maximum to 3.5 × 10–3 Ω cm with a Seebeck coefficient of 115 μV/K at room temperature, which increases to 175 μV/K at 600 K. These electrical properties are almost identical to those of the well-known p-type oxide thermoelectric NaxCoO2. Nonmagnetic Li-substituted PbPdO2 does not possess a correlated, magnetic state with high-spin ...

Hard materials used in such abrasive wear applications as cutting tools and wear inserts in drilling tools require high hardness to resist wear, high fracture toughness to withstand mechanical and thermal shock, and high chemical and thermal stability. Such a combination of properties is difficult to achieve in single-phase materials. Functional grading is an approach that overcomes this limitation by designing and processing a graded microstructure that provides high hardness and chemical resistance at the surface with a tough interior or bulk. While functional grading is a widely used practice in the cemented carbides industry, it has not been demonstrated with “pure” carbides. This article reports the feasibility of designing and processing a graded carbide in the Ta–C binary system. It is shown that a simple carburization treatment of the high-toughness carbide, ζ-Ta4C3−x, can lead to the formation of the hard carbide phase, γ-TaCy, on the surface. The thickness, microstructure (grain size), and composition (C/Ta atomic ratio, y) of the γ-TaCy layer can be optimized to obtain both high hardness and high strength for the graded material.

In this review, we describe the creation of a large database of thermoelectric materials prepared by abstracting information from over 100 publications. The database has over 18 000 data points from multiple classes of compounds, whose relevant properties have been measured at several temperatures. Appropriate visualization of the data immediately allows certain insights to be gained with regard to the property space of plausible thermoelectric materials. Of particular note is that any candidate material needs to display an electrical resistivity value that is close to 1 mΩ cm at 300 K, that is, samples should be significantly more conductive than the Mott minimum metallic conductivity. The Herfindahl–Hirschman index, a commonly accepted measure of market concentration, has been calculated from geological data (known elemental reserves) and geopolitical data (elemental production) for much of the periodic table. The visualization strategy employed here allows rapid sorting of thermoelectric compositions w...

The thermal diffusivity of the La-doped layered perovskite Sr2Nb2O7 parallel and perpendicular to the perovskite layers is reported from room temperature up to 1000°C. The anisotropy persists through an incommensurate-normal ferroelectric phase transformation at 215°C and up to 1000°C, the maximum temperature of our measurements. The thermal conductivity perpendicular to the perovskite layers, derived from the diffusivity in the same direction, calculated using the density and measured heat capacity, has a constant value of 1.05±0.05 W/mK up to 1000°C. Possible explanations for the low thermal conductivity and anisotropy are described.

The thermal conductivity of a series of complex aluminates, RE2SrAl2O7, with different rare-earth (RE) ions, has been measured up to 1000°C. There is a strong dependence on the atomic number of the RE ion, ranging from an approximately 1/T dependence for the lanthanum strontium aluminate to an almost temperature-independent behavior of the dysprosium strontium aluminate. The latter conductivity is comparable with that of yttria-stabilized zirconia, the current material of choice for thermal barrier coatings. The temperature dependence of the thermal conductivities of all the aluminates studied can be fit to a standard phonon–phonon scattering model, modified to account for a minimum phonon mean free path, in which the difference in behavior is attributed to increased phonon–phonon scattering with the atomic mass of the RE ion. Although a satisfactory parametric fit is obtained, the model does not take into account either the detailed layer structure of the aluminates, consisting of alternating rock-salt and perovskite layers in a natural superlattice structure, or the site preferences of the RE ion. This suggests that further model development is warranted.

A large n-type thermopower of −73 μV K−1 was observed at high temperatures (1100 K) for the first time in the mixed valence (Mn3+/Mn4+) spinel oxide LiMn2O4. The absence of a Jahn–Teller distortion leads to an electronic degeneracy ratio of 10/4 rather than 5/4 in the Heikes formula for the spin degeneracy contribution to the thermopower.