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We present work on the application of sequential supervised machine learning for a reduced-dimension, ballistic deposition, Monte Carlo particle packing. Calculations are carried out for a combination of three distinguishable hard spheres representing different materials. Each set of spheres has a distribution of particle sizes in order to mimic realistic milling conditions of raw ingredients. Since infinite combinations of particle size, distribution, fraction, and density exist, we employ machine learning to aid in the design optimization of new high packing density mixtures. Previously calculated binary packs of particle radius ratios of 80:1 were analyzed, but this work highlights results of ternary packs with radius ratios greater than 300:1. We demonstrate a sequential learning approach where iterative experiments are performed based on minimizing the uncertainty in the target regime of high packing density. New candidate mixtures are identified via classification rather than regression which provides superior ability to extrapolate into high packing density mixtures.

Thermoelectrics (TEs) are an important class of technology that harvest electric power directly from heat sources. When designing both high performance and environmentally friendly TE materials, the pseudo-cubic structure has great theoretical potential to maximize the dimensionless figure of merit ZT. The TE multinary single crystal with a pseudo-cubic structure paves a new path toward manipulating valley degeneracy and anisotropy with low thermal conductivity caused by short-range lattice distortion. Here, we report a record high ZT = 1.6 around 800 K realized in a totally environmentally benign p-type Na-doped Cu2ZnSnS4 (CZTS) single crystal. The exceptional performance comes from a high power factor while maintaining intrinsically low thermal conductivity. The combination of the pseudo-cubic structure and intrinsic properties of the CZTS single crystal takes advantage of simple material tuning without complex techniques.

Over the past 150 years, our ability to produce and transform engineered materials has been responsible for our current high standards of living, especially in developed economies. However, we must carefully think of the effects our addiction to creating and using materials at this fast rate will have on the future generations. The way we currently make and use materials detrimentally affects the planet Earth, creating many severe environmental problems. It affects the next generations by putting in danger the future of the economy, energy, and climate. We are at the point where something must drastically change, and it must change now. We must create more sustainable materials alternatives using natural raw materials and inspiration from nature while making sure not to deplete important resources, i.e. in competition with the food chain supply. We must use less materials, eliminate the use of toxic materials and create a circular materials economy where reuse and recycle are priorities. We must develop sustainable methods for materials recycling and encourage design for disassembly. We must look across the whole materials life cycle from raw resources till end of life and apply thorough life cycle assessments (LCAs) based on reliable and relevant data to quantify sustainability. We need to seriously start thinking of where our future materials will come from and how could we track them, given that we are confronted with resource scarcity and geographical constrains. This is particularly important for the development of new and sustainable energy technologies, key to our transition to net zero. Currently ‘critical materials’ are central components of sustainable energy systems because they are the best performing. A few examples include the permanent magnets based on rare earth metals (Dy, Nd, Pr) used in wind turbines, Li and Co in Li-ion batteries, Pt and Ir in fuel cells and electrolysers, Si in solar cells just to mention a few. These materials are classified as ‘critical’ by the European Union and Department of Energy. Except in sustainable energy, materials are also key components in packaging, construction, and textile industry along with many other industrial sectors. This roadmap authored by prominent researchers working across disciplines in the very important field of sustainable materials is intended to highlight the outstanding issues that must be addressed and provide an insight into the pathways towards solving them adopted by the sustainable materials community. In compiling this roadmap, we hope to aid the development of the wider sustainable materials research community, providing a guide for academia, industry, government, and funding agencies in this critically important and rapidly developing research space which is key to future sustainability., The authors would like to thank The Faraday Institution ReLiB Project Grant Numbers FIRG005 and FIRG006, the UKRI Interdisciplinary Circular Economy Centre for Technology Metals (Met4Tech) Grant No. EP/V011855/1 and the EPSRC Critical Elements and Materials Network (CREAM) EP/R020140/1 for providing financial assistance for this research.

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...

Porosity-graded, conductor- and binder-free porous FeS2 films through the entire thickness were deposited by spray pyrolysis. The film layers deposited at 15 versus 10 L/min are grown in different modes. The film layer deposited at 15 L/min showed Frank–van der Merwe layer-like growth mode whereas the one deposited at 10 L/min showed island growth mode. These growth modes lead to the formation of large pores on the electrolyte side and small ones on the substrate side of the film deposited using 15 and 10 L/min, sequentially. The porosity-graded films showed discharge capacities at C/10 of 879 mA h/g and 754 mA h/g for the 5th and 20th cycles, respectively. Such capacity values are superior to the literature findings for FeS2 powders and nongraded films mixed with conductor and binder additions.

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.

Mo0.9W1.1BC and ReWC0.8 compositions have recently been identified to have exceptional hardness and incompressibility. In this work, these compositions are analyzed via in situ radial X-ray diffraction experiments to comparatively assess lattice strain and texture development. Traditionally, Earth scientists have employed these experiments to enhance understanding of dynamic activity within the deep Earth. However, nonhydrostatic compression experiments provide insight into materials with exceptional mechanical properties, as they help elucidate correlations between structural, elastic, and mechanical properties. Here, analysis of differential strain (t/G) and lattice preferred orientation in Mo0.9W1.1BC suggests that dislocation glide occurs along the (010) plane in orthorhombic Mo0.9W1.1BC. The (200) and (002) planes support the highest differential strain, while planes which bisect two or three axes, such as the (110) or (191), exhibit relatively lower differential strain. In ReWC0.8, which crystallizes in a cubic NaCl-type structure, planar density is correlated to orientation-dependent lattice strain as the low-density (311) plane elastically supports more differential strain than the denser (111), (200), and (220) planes. Furthermore, results indicate that ReWC0.8 likely supports a higher differential stress t than Mo0.9W1.1BC and, based on a lack of texture development, bulk plastic yielding is not observed in ReWC0.8 upon compression to ∼60 GPa.

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.

To improve battery performance a high cathode surface area is needed to maximize the electrode–electrolyte contact area. For this purpose, and for the first time, conductor- and binder-free porous FeS2 films through the entire thickness were deposited by spray pyrolysis. 1 M of Fe(NO3)3.9H2O, FeCl3, and NH2CSNH2 were utilized as the precursors. Film deposition was performed at 400 °C in open atmosphere. The deposited films were then sulfurized at 500 °C for 4 h with H2S gas or in sealed quartz ampoules with sulfur flakes. The best crystallized films were obtained using FeCl3 and NH2CSNH2 precursors followed by sulfurization in the sealed ampoules. The films were characterized with X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The films were cycled at C/10 and C/20 and despite having no binder or conductive additives gave comparable capacities compared to the literature finding for FeS2 powders mixed with conductor and binder additions.

Electrochromic materials and devices are enabling a variety of advanced technologies. Gel-based organic electrochromic molecules such as ethyl viologen diperchlorate are attractive options due to their simple device design and low cost processing options relative to the more expensive and complex transition metal oxide films. However, electrochromic devices are subject to extensive cycling in which failure and fatigue can eventually occur. This work presents the lifetime cycling performance of ethyl viologen diperchlorate-based electrochromic devices using two different anodic compounds, hydroquinone and ferrocene, which are cycled at different voltages, 3 V and 1.2 V, respectively. Multiple devices are cycled until failure with periodic device characterization via UV–Vis spectroscopy, electrical resistance and power measurement, and transition duration measurement. Devices with hydroquinone can transition quickly. Cycle times are $$\sim$$ ∼ 30 s in these samples, however, these samples also typically fail before 3000 cycles. On the other hand, devices using ferrocene transition more slowly (total cycle time $$\sim$$ ∼ 2 min), but have superior cycling performance with all samples surviving beyond 10,000 cycles while complying with ASTM E2141-14 standard.

Thermoelectrics (TEs) are an important class of technologies for harvesting electric power directly from heat sources. To design high performace TE materials, valleytronics has great theoretical potential to maximize a dimensionless figure of merit ZT but has not yet been demonstrated experimentally. Pseudocubic structure approach based on valleytronics paves a new path to manipulate valley degeneracy and anisotoropy with low thermal conductivity caused by short-range lattice distortion. Here, we report a record high ZT = 1.6 around 800 K, realized in totally enviromentally benign Na-doped Cu2ZnSnS4 (CZTS) single crystal. The exceptional performance comes from a high power factor while maintaining intrinsically low thermal conductivity. The results demonstrate that valleytronics is a new strategy and direction in the TE field, which takes advantage of simple material nature tuning without complex techniques.

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.

Solid-state lighting using laser diodes is an exciting new development that requires new phosphor geometries to handle the greater light fluxes involved. The greater flux from the source results in more conversion and therefore more conversion loss in the phosphor, which generates self-heating, surpassing the stability of current encapsulation strategies used for light-emitting diodes, usually based on silicones. Here, we present a rapid method using spark plasma sintering (SPS) for preparing ceramic phosphor composites of the canonical yellow-emitting phosphor Ce-doped yttrium aluminum garnet (Ce:YAG) combined with a chemically compatible and thermally stable oxide, α-Al2O3. SPS allows for compositional modulation, and phase fraction, microstructure, and luminescent properties of ceramic composites with varying compositions are studied here in detail. The relationship between density, thermal conductivity, and temperature rise during laser-driven phosphor conversion is elucidated, showing that only modes...

Two α-alumina + YSZ samples were prepared by sintering for 3 h one at 1500 °C and the other at 1700 °C. The samples were then converted to Na-β″-alumina + YSZ by vapor phase conversion. Characterization techniques such as X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy in addition to dimensional geometrical changes reveal the evolution of slight anisotropy in these samples during conversion. This results in an electrical conductivity anisotropy factor of about 5.5 and 1.8 for samples sintered at 1500 °C and 1700 °C, respectively. In all samples, the higher ionic conductivity was measured across the sample thickness as opposed to parallel to the disc faces. The ionic conductivity measurements show the conductivity of about 0.15 S/cm and 0.07 S/cm at 300 °C for samples sintered at 1500 °C and 1700 °C, respectively. The larger anisotropy in samples sintered at 1500 °C is explained by the higher aspect ratio of grains in this sample and by different Na concentrations.

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 .

In this paper we investigate the high-temperature structure of ${\mathrm{Co}}_{3}{\mathrm{O}}_{4}$, a compound that has been studied extensively over the last 60 years due to its unresolved high-temperature structure. In situ thermal analysis and x-ray diffraction confirm previously reported high-temperature structural changes and show that these changes are unrelated to the high-temperature decomposition to CoO. Raman-active peaks are also extinguished over the same temperature range. By considering the changing lattice parameter, $A$-O, and $B$-O bond lengths as well as cation size we are able to calculate the degree of inversion which reaches a maximum of 0.6. To further study the structure in this experimentally inaccessible range we quench samples and perform ex situ measurements including redox titration, x-ray photoelectron spectroscopy, and neutron diffraction. We do not observe any evidence of large oxygen vacancy concentrations or octahedral ${\mathrm{Co}}_{B}{}^{3+}$ ions with high spin state. However, we do show an evolution in the magnetic moment from magnetic structure refinement from ($2.4\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\text{B}}$) to ($2.7\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\text{B}}$) that coincides exactly with the high-temperature anomaly and suggests partial inversion (0.46) of the spinel structure in fairly good agreement with the inversion calculated from bond lengths.

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.

Two phase samples containing ~ 30 vol.% of 3 mol% Y2O3-stabilized zirconia (TZ-3Y) and ~ 70 vol.% of α-Al2O3 doped with 5 mol% Fe2O3 were fabricated by sintering powder compacts in air at 1450 °C. The added Fe2O3 was fully dissolved in Al2O3 as determined by X-ray diffraction. The two phase samples were packed in Na-β”-alumina powder of nominal composition 8.85 wt.% Na2O, 0.75 wt.% Li2O and balance Al2O3 and heat treated in air at 1250 °C for 20 h. The samples were sectioned, polished and examined by X-ray diffraction, optical microscopy and scanning electron microscopy. The as-sintered samples were ~ 97% of theoretical density with an approximate grain size of ~ 0.8 μm. In the samples packed in Na-β”-alumina powder and heat treated in air, Fe-doped α-Al2O3 converted into Fe-doped Na-β”-alumina. A sample of 2.35 mm in thickness could be fully converted into iron-doped Na-β”-alumina in 17 h at 1450 °C. Ionic conductivity was measured by electrochemical impedance spectroscopy (EIS) over a temperature range from 197 °C to 485 °C. The bulk conductivity of the converted sample exhibited Arrhenius behavior with an activation energy of 0.20 eV and a pre-exponential factor of 421 Ω− 1cm− 1 K.

Dialysis is the process by which an artificial kidney device removes waste and excess water from a patient. An outstanding problem with dialysis is that the body has a remarkable immune function where proteins and antigens mark foreign objects as possible threats despite the biocompatibility of the material. Upon adhesion to polymeric materials used currently in dialysis, proteins are lost. In this study, polytetrafluoroethylene (PTFE) is investigated as a potential replacement material for dialysis tubing because of its unreactive nature. The focus is to determine if PTFE will prove a viable material in minimizing protein adhesion and further reducing antibody loss of the patient. Protein loss as a function of filtration time was measured. PVC and PTFE materials were investigated following the same battery of testing where the protein concentrations in the blood were characterized using UV Visible spectrophotometry. Results demonstrate a loss of nearly 12 percent of blood proteins to the PVC material over the course of a typical dialysis treatment. Conversely, the protein loss due to adhesion to PTFE was less than two percent.

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 ...

In this article we provide an overview of data mining, informatics, and machine learning approaches for thermoelectrics. We describe how the initial development of a thermoelectric materials database has enabled the creation of a recommendation engine governed by machine learning and how this engine introduces a new paradigm in thermoelectric materials development. Performance probability is generated based on training models. A demonstration of the data mining approach is set forth in a ternary intermetallic system, where we report new materials.

This study evaluates performance of passive thermal management system of high power Li-ion batteries in a cold environment. Two different phase change materials (PCM) consisting of pure paraffin and paraffin–graphite composites are considered and compared with a battery module in absence of PCM material. Battery modules are partially discharged for a period and then subjected to different cold time periods representing short and long vehicle stops during winter. Battery performance parameters such as capacity, power, and temperature along with thermophysical properties of each module are recorded, calculated, and compared for different scenarios. Thermal management systems moderate temperature rise during discharge and slow the temperature loss during cold stops but also slow the temperature rise after cold stops. Results show that after a short (10 min) cold stop the paraffin wax offers no advantage by keeping the module warm. Both paraffin and no PCM modules had comparable energy values. On the other hand, during long (2 hours) cold stops a significant detriment (15% reduced energy vs 6% reduced energy) was observed in PCM modules by delaying battery warm up when compared to modules with no PCM. Commercial PCM modules with graphite/paraffin composites performed in-between PCM and no PCM modules (9% reduced energy) after long cold soaks but had no advantage for short cold soaks (2.5% energy reduction) due to higher heat dissipation. Keywords: Thermal management system, Phase change material, Lithium-ion battery

In this work we present a data-driven approach to the rational design of battery materials based on both resource and performance considerations. A large database of Li-ion battery material has been created by abstracting information from over 200 publications. The database consists of over 16 000 data points from various classes of materials. In addition to reference information, key parameters and variables determining the performance of batteries were collected. This work also includes resource considerations such as crustal abundance and the Herfindahl–Hirschman index, a commonly used measure of market concentration. The data is organized into a free web-based resource where battery researchers can employ a unique visualization method to plot database parameters against one another. This contribution is concerned with cathode and anode electrode materials. Cathode materials are mostly based on an intercalation mechanism, while anode materials are primarily based on conversion and alloying. Results indicate that cathode materials follow a common trend consistent with their crystal structure. On the other hand anode materials display similar behavior, based on elemental composition. Of particular interest is that high energy cathodes are scarcer than high power materials and high performance anode materials are less available. More sustainable materials for both electrodes based on alternative compositions are identified.

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 apatite crystal structure of the gadolinium calcium silicates can accommodate a wide range of point defects, including oxygen and cation vacancies, as well as anti-site defects, depending on the Gd/Ca ratio. Compositions having only cation or oxygen vacancies were identified and the thermal diffusivity and conductivity were measured up to 1000 C. All the compositions, including the stoichiometric composition, exhibit low thermal conductivities from room temperature to high temperature with the defect-containing compositions having even lower thermal conductivities. The high-temperature thermal conductivity, at temperatures below the onset of significant radiative heat transport, decreases with the inverse square root of the cation and anion vacancy concentration, consistent with simple defect scattering models. Based on the data, it is concluded that the oxygen vacancies are slightly more effective in reducing thermal conductivity.

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.

Composite electrolytes composed of Sm 3+ and Nd 3+ co-doped ceria (SNDC) and binary carbonates (Li 2 CO 3 –Na 2 CO 3 ) were investigated with respect to their microstructure, morphology and electrical conductivity. As a function of temperature, the electrical conductivity of the composite electrolytes was measured in air. The addition of (Li/Na) 2 CO 3 to SNDC enhanced the high temperature conductivity. The conductivity also rose sharply around the intenerating and melting point of carbonates. The best performance of 0.01 S/cm at 481 °C was achieved for the composite electrolyte containing 20 wt.% carbonates. It is also estimated that the reason for the conductivity enhancement of SNDC is that the number of oxygen transfer routes increases at the interface between SNDC and (Li/Na) 2 CO 3 .

Molecular imprinting is the process by which molecules are imprinted into the matrix of a material through non-covalent bonding, including hydrogen bonding and van der Waals interactions. In this study hydrogels were imprinted with glaucoma medication with the purpose of creating a reusable ocular drug delivery device with reversible binding sites. The material was synthesized and tested with UV-Vis spectroscopy to determine the concentration of the released drug after twelve hours in distilled water. Modifications were made to the polymer to explore methods required for the proper delivery of the drug over an adequate period of time.

The spinel NiCr$_2$O$_4$ is characterized using dielectric and high magnetic field measurements. The trends in the magnetodielectric response fall into three clear temperature regimes corresponding to known magnetic and structural transitions. Above 65\,K, weak magnetic field dependence of the dielectric constant is observed with no hysteresis. When 30\,K\,$\leq\,T\,\leq$\,65\,K, a strong dependence of the dielectric constant on the magnetic field is observed and hysteresis develops resulting in so called butterfly loops. Below 30\,K, magnetodielectric hysteresis is enhanced. Magnetodielectric hysteresis mirrors magnetic hysteresis suggesting that spin-spin interactions are the mechanism for the magnetoelectric effect in NiCr$_2$O$_4$. At high fields however, the magnetization continues to increase while the dielectric constant saturates. Magnetodielectric measurements of NiCr$_2$O$_4$ suggest an additional, previously unobserved transition at 20\,K. Subtle changes in magnetism and structure suggest that this 20\,K anomaly corresponds to the completion of ferrimagnetic ordering and the spin driven structural distortion. We demonstrate that magnetocapacitance is a sensitive probe of magnetostructural distortion.

Half-Heusler XYZ compounds with an 18 valence electron count are promising thermoelectric materials, being thermally and chemically stable, deriving from relatively earth-abundant components, and possessing appropriate electrical transport properties. The typical drawback with this family of compounds is their high thermal conductivity. A strategy for reducing thermal conductivity is through the inclusion of secondary phases designed to minimize negative impact on other properties. Here, we achieve this through the addition of excess Co to half-Heusler NbCoSn, which introduces precipitates of a semi-coherent NbCo2Sn Heusler phase. A series of NbCo1+xSn materials are characterized here using X-ray and neutron diffraction studies and electron microscopy. Electrical and thermal transport measurements and electronic structure calculations are used to understand property evolution. We find that annealing has an important role to play in determining antisite ordering and properties. Antisite disorder in the as-...

The experimental search for new thermoelectric materials remains largely confined to a limited set of successful chemical and structural families, such as chalcogenides, skutterudites, and Zintl phases. In principle, computational tools such as density functional theory (DFT) offer the possibility of rationally guiding experimental synthesis efforts toward very different chemistries. However, in practice, predicting thermoelectric properties from first principles remains a challenging endeavor [J. Carrete et al., Phys. Rev. X 4, 011019 (2014)], and experimental researchers generally do not directly use computation to drive their own synthesis efforts. To bridge this practical gap between experimental needs and computational tools, we report an open machine learning-based recommendation engine (http://thermoelectrics.citrination.com) for materials researchers that suggests promising new thermoelectric compositions based on pre-screening about 25 000 known materials and also evaluates the feasibility of user-designed compounds. We show this engine can identify interesting chemistries very different from known thermoelectrics. Specifically, we describe the experimental characterization of one example set of compounds derived from our engine, RE12Co5Bi (RE = Gd, Er), which exhibits surprising thermoelectric performance given its unprecedentedly high loading with metallic d and f block elements and warrants further investigation as a new thermoelectric material platform. We show that our engine predicts this family of materials to have low thermal and high electrical conductivities, but modest Seebeck coefficient, all of which are confirmed experimentally. We note that the engine also predicts materials that may simultaneously optimize all three properties entering into zT; we selected RE12Co5Bi for this study due to its interesting chemical composition and known facile synthesis.

Searchable, interactive, databases of material properties, particularly those relating to functional materials (magnetics, thermoelectrics, photovoltaics, etc.) are curiously missing from discussions of machine-learning and other data-driven methods for advancing new materials discovery. Here we discuss the manual aggregation of experimental data from the published literature for the creation of interactive databases that allow the original experimental data as well additional metadata to be visualized in an interactive manner. The databases described involve materials for thermoelectric energy conversion, and for the electrodes of Li-ion batteries. The data can be subject to machine-learning, accelerating the discovery of new materials.

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.

Reduced early transition metal oxides/metal composites have been identified here as interesting thermoelectric materials. Numerous compositions in the Nb-rich portion of the WO3–Nb2O5 system have been studied, in composite formulations with elemental W. Spark plasma sintering (SPS) has been employed to achieve rapid preparation and consolidation of composite materials containing W metal precipitates with characteristic length scales that range from under 20 nm to a few microns, that exhibit thermal conductivities that are constant from 300 K to 1000 K, approximately 2.5 W m−1 K−1. Thermoelectric properties of these n-type materials were measured, and the highest-performing compositions were found to reach figure of merit zT values close to 0.1 at 950 K. The measurements point to higher zT values at yet-higher temperatures.

Large improvements in the performance of thermoelectric materials have come from designing materials with reduced thermal conductivity. Yet as the thermal conductivity of some materials now approaches their amorphous limit, it is unclear if microstructure engineering can further improve thermoelectric performance in these cases. In this contribution, we use large data sets to examine 300 compositions in 11 families of thermoelectric materials and present a type of plot that quickly reveals the maximum possible zT that can be achieved by reducing the thermal conductivity. This plot allows researchers to quickly distinguish materials where the thermal conductivity has been optimized from those where improvement can be made. Moreover, through these large data sets we examine structure-property relationships to identify methods that decrease thermal conductivity and improve thermoelectric performance. We validate, with the data, that increasing (i) the volume of a unit cell and/or (ii) the number of atoms in the unit cell decreases the thermal conductivity of many classes of materials, without changing the electrical resistivity.

The development of superhard materials is focused on two very different classes of compounds. The first contains only light, inexpensive main group elements and requires high pressures and temperatures for preparation whereas the second class combines a transition metal with light main group elements and in general tends to only need high reaction temperatures. Although the preparation conditions are simpler, the second class of compounds suffers from the transition metals used being expensive and exceedingly scarce. Thus, in the search for novel superhard compounds, synthetic accessibility, resource considerations, and material response must be balanced. The research presented here develops high-information density plots drawn from high-throughput first-principle calculations and data mining to reveal the optimal composition space to synthesize new materials. This contribution includes analysis of the experimentally known Vickers hardness for materials as well as screening over 1100 compounds from first-principle calculations to predict their intrinsic hardness. Both data sets are analyzed not only for their mechanical performance but also the compositional scarcity, and Herfindahl-Hirschman index is calculated. Following this methodology, it is possible to ensure targeted materials are not only sustainable and accessible but that they will also have superb mechanical response.