Poor Metal Research Articles

Enhanced Thermoelectric Transport Properties of <i>n</i>-type InSe by Sn doping

Layered post transition metal chalcogenides such as SnSe, SnSe<sub>2</sub>, In<sub>2</sub>Se<sub>3</sub>, and In<sub>4</sub>Se<sub>3</sub> have attracted attention as promising thermoelectric materials due to their intrinsically low lattice thermal conductivities. Recently, <i>n</i>-type indium selenide (InSe) based materials have also been suggested as good candidates for thermoelectric materials by optimizing their electrical properties, i.e., increasing carrier concentration. Here, we report enhancement of the thermoelectric properties of <i>n</i>-type InSe by Sn substitutional doping at the In site. A series of In<sub>1-x</sub>Sn<sub>x</sub>Se for x = 0, 0.03, 0.05, 0.15 and 0.2 was examined. The carrier concentration and electrical conductivity increased due to the Sn substitution, since Sn behaves as a shallow electron donor in InSe, while the Seebeck coefficient decreased moderately. In addition, it was found that effective mass was increased by more than 10 times by Sn doping. As a result, the power factor was enhanced from 0.07 mW/mK<sup>2</sup> to 0.13 mW/mK<sup>2</sup> at 800 K. The total thermal conductivity was unchanged despite Sn doping because the electrical contribution to the total thermal conductivity was very small. Consequently, Sn doping in InSe enhanced the dimensionless thermoelectric figure of merit <i>zT</i> from 0.04 to 0.14 at 800 K, mainly due to enhanced electrical properties.

Measurement of ultrashort laser ablation of four metals (Al, Cu, Ni, W) in the single-pulse regime

Abstract We provide measurements of the ablation of four post-transition and transition metals [aluminum (Al), copper (Cu), nickel (Ni) and tungsten (W)] irradiated by single 800 nm laser pulses, in ultrashort regime from 100 femtosecond (fs) pulse duration down to 15 fs covering a temporal range little explored as yet. For each metal and pulse duration tested, we measured its ablation characteristics (depth and diameter) as a function of incident energy allowing us to determine its laser-induced ablation threshold and ablation rate in a single-shot regime. For all the metals studied, we observed a constant ablation threshold fluence as a function of pulse duration extending this scaling law to pulse duration of few-optical-cycles. We provide evidence of the interest of adjusting the incident fluence to maximize the energy specific ablation depth but also of the absence of any peculiar advantage related to the use of extremely short-pulse duration for ablation purposes. Those informative and detailed ablation data have been obtained in the single-pulse regime and in air ambiance. They can serve as rewarding feedback for further establishing smart strategy for femtosecond laser micromachining and laser damage handling of metallic and metal-based components as well as for enhancing accuracy of modeling of fs laser interaction with metals in ultrashort regime.

(Keynote) New Classes of Copper-Free Electrocatalysts for CO2 Reduction Based on Transition Metal/Post Transition Metal Alloys and Intermetallic Compounds

Binary alloys and intermetallic compounds composed of a first row transition metal and a post transition metal such as aluminum or gallium provide a new source of heterogeneous electrocatalysts for the reduction of CO2. Unlike the related Group 13 and 14 single metal systems (tin and indium which only generate formate and CO, the mixed metal systems form a variety of C1 products, along with carbon-carbon bonded products. The alloy systems resemble the indium and tin systems, in that they show a catalytic dependence on the surface oxides present.We have reported that Ni3Al reduces CO2 to a variety of C3 oxygenates,1-2 while Lewis et. al. has noted that various NixGay alloys generate C2 products from CO2.3 In both cases, the higher order products are observed in low yield. However, these examples are important since they demonstrate that metallic systems that do not contain copper can form carbon-carbon bonds from CO2. Recently we discovered that chromium-gallium bimetallic combinations can produce oxalate in high faradaic yields in aqueous electrolytes.4 Here again an oxide plays a key role in the observed electrocatalysis.The Cr-Ga system, which may best be thought of as an alloy of Cr2O3 and Ga2O3 is particularly intriguing since it produces oxalate at modest potentials (~-1.5 V vs. Ag/AgCl) in aqueous electrolyte. Prior reports on oxalate electrogeneration from CO2 required the use of nonaqueous electrolytes and significantly more negative potentials (>-2.0 V vs. Ag/AgCl). In the current system, we find that CO2 reduction can be carried out at potentials where oxalate formation competes favorably with H2 production yielding faradaic efficiencies in excess of 50%. Our new findings argue for a previously unexplored mechanism for the formation of carbon-carbon bonds that circumvents the generation of a [CO2 –• ] intermediate. Preliminary data hints at a mechanism that goes through a CO intermediate. Interestingly this system is strongly cation dependent, showing reactivity patterns that suggest two distinct active sites are present at the electrode interface.For all of the alloy and intermetallic systems we have investigated, there appears to be strong correlation between the morphology of the mixed metal electrocatalyst and the product distribution. The chemical source of this effect remains under study. It is also observed that the composition of the underlying electrode strongly influences the product composition. For example, while Ni3Al on glassy carbon produces a variety of C3 products, the same catalyst when placed on a p-type CIGS photocathode primarily produces methanol with no indication of carbon-carbon coupling processes.A detailed mechanistic understanding of these systems is likely to offer new opportunities for the electrosynthesis of organic products from CO2 with high faradaic yield and modest overpotential.

Origin of high carrier concentration in amorphous wide-bandgap oxides: Role of disorder in defect formation and electron localization in In2O3−x

Structural disorder has been known to suppress carrier concentration and carrier mobility in common covalent semiconductors, such as silicon, by orders of magnitude. This is expected from a reduced overlap of the electron clouds on neighboring orbitals and the formation of localized tail states near the band edges caused by local distortions and lack of periodicity in the amorphous phase. In striking contrast to the covalent semiconductors, wide-bandgap oxides of post-transition metals with ionic bonding not only allow for crystalline-like electron mobility upon amorphization, but also exhibit two orders of magnitude higher carrier concentration in the disordered phase as compared to the crystalline oxide. Here, the results of computationally intensive ab initio molecular dynamics simulations, comprehensive structural analysis, and accurate density-functional calculations reveal complex interplay between local distortions, coordination, and long-range bond morphology and help establish the microscopic origin of carrier generation and transport across the crystalline–amorphous transition in In2O3−x. Departing from traditional oxygen vacancy in crystalline oxides, the derived structural descriptors help categorize “defects” in disordered ionic oxides, quantify the degree of the associated electron localization and binding energy, and determine their role in the resulting electronic and optical properties. The results will be instrumental in the development of next-generation transparent amorphous semiconductors with a combination of properties not achievable in Si-based architectures.

(Invited) Correlation in 2D Materials: Proximity Effects and Reactivity through the Lens of Quantum Monte Carlo

2D materials are an exciting new class of materials promising for a wide range of engineering applications because of their exceptionally tunable electronic properties; indeed, these materials’ band gaps, charge densities, and spin densities can be dramatically altered just by stretching, compressing, or stacking them. Despite their promise, however, our modern understanding of 2D materials is partially obscured by the fact that most have only been computationally modeled using Density Functional Theory (DFT), a theory that cannot readily describe electron correlation and is known to yield widely varying results for such integral quantities as band gaps and molecular binding energies depending upon the exchange-correlation functional employed. In this talk, I will describe our recent efforts to model an array of 2D materials using fully correlated quantum Monte Carlo (QMC) techniques and the unanticipated physics these efforts have revealed. First, we will discuss for which materials our simulations reveal the largest discrepancies between DFT and QMC. We will then illustrate the importance of using correlated methods in the modeling of proximity-induced magnetism and spin-orbit coupling in multilayer materials. Lastly, if time permits, we will detail how correlation influences carbon dioxide reduction on post-transition metal chalcogenides. Altogether, this work paints a more complete picture of the electronic structure of this increasingly important class of materials.

Proton induced L-shell cross-sections for some post-transition metals: A comparison of ECPSSR and SCA models

The L-shell ionisation and X-ray production cross-sections of some post-transition elements: In, Sn and Tl, induced by protons of energies 1 MeV–4 MeV, have been calculated. The targets considered have few experimental cross-sections, for indium and tin, while thallium has no existing cross-section values in the database due to its radioactive and toxic nature. The cross-sections for the targets were obtained using computer codes based on the ECPSSR and SCA theories; and were subsequently validated using lead and bismuth targets whose experimental values are known within this energy range. The comparison of the experimental and calculated cross-sections showed that both models are in good agreement within certain proton energy region. However, above 2 MeV, the ECPSSR models should be employed. For the case where the SCA model is to be employed, the energy loss and Coulomb deflection factors should be taken into account.

Indium as a critical mineral: A research progress report

Indium (In) is a post-transition metal of Group 13 in the Periodic Table. It is a highly volatile chalcophile element which behaves in a moderately to highly incompatible manner. Abundance of indium in the continental crust is estimated at 0.01 ppm. Indium has been widely used in high-tech products, especially in emerging industry technology and national defense and security sectors. Therefore, it is called “critical mineral” in developed countries. Indium becomes one of the critical metals to support vigorous development of China’s emerging strategic industries. More than 90% of indium is recovered as a by-product of zinc mining. The most recent assessment of global indium reserves in 2018 was 79000 tones. China accounts for more than 18.2% of global indium reserves, while Peru, Canada, USA and Russia together own more than 62.4%. Indium occurs in different types of ore deposits. Indium-rich deposits include volcanic- and sediment-hosted exhalative massive sulfide deposits, epithermal deposits, polymetallic base metal vein-type deposits, granite-related tin-base-metal deposits, skarn deposits and porphyry copper deposits. These deposits are commonly associated with active oceanic or continental plate margins and orogenic belts with steep geothermal gradients due to enhanced magmatic activities. Most of indium deposits are associated with highly differentiated granites. Biotite is the main carrier mineral of indium. Recent research indicates that the enrichment of indium does not increase with the increase of crystallization differentiation in felsic magmatic systems. The increase of magnesium concentration in biotite reduces the potential of indium mineralization. The joint action of alkaline and sub-alkaline mafic and granitic magmas is an important prerequisite for the formation of high-grade indium deposits. Volcanic systems provide favorable conducive environment for the enrichment of indium. There are few studies on the enrichment of indium in silicate minerals. Garnet is a major tin-bearing skarn mineral at the Dulong Sn-Zn deposit of Yunan Province. Based on LA-ICP-MS analysis, indium concentration is 166.0–629.0 ppm in the garnet that was formed in the early skarn stage and 1.6–10.0 ppm in the garnet that was formed in the late skarn stage. The data indicate that the earlier garnet is enriched in indium than the later one. The data also show that indium has an apparent covariant relationship with tin, but an inverse correlation with aluminum. Multi-stage fluid activities in the evolution of magmatic hydrothermal processes are the key to enrichment of indium. Overprinting of multi-stage hydrothermal processes plays an important role in the formation of high-grade indium deposits. For example, indium-rich sphalerite in the Hammerlein skarn polymetallic deposit in Germany occurs around the early indium-free sphalerite grain, demonstrating overprinting of later indium-rich ore fluids. There are three ways for indium to substitute for zinc in sphalerite: (1) Cu++In3+↔2Zn2+, (2) Cu+/Ag++In2+↔2Zn2+, and (3) In3++Sn3++(vacancy)↔3Zn2+. The substitute of indium for zinc in sphalerite is slightly different due to the ore-formingelement (Cu, Ag, Sn, Ga, Ge, etc.). Tin can replace zinc with different valence state and other elements depending on the precipitation environment of sphalerite. Recent studies have shown that there are “indium window” and “indium explosion” that exist during the process of indium mineralization. Modern analytical technology and experimental simulation reveal the mechanism for “indium explosion” effect in the Dulong Sn-Zn deposit of Yunan Province. In this mechanism, lattice displacement and vacancies in small number within sphalerite facilitate indium enrichment in {111} direction in sphalerite. In summary, several items should be followed for the future research and exploration of resources of critical mineral indium: (1) Fully understand the occurrence state of indium in major carrier minerals and reveal mechanism for selective super-enrichment of indium; (2) improve our understanding of indium enrichment mechanism in different geological settings, which would effectively guide future exploration of indium deposits; (3) renovate indium recycling technologies and seek its substitutes.

Expression and interactions of stereochemically active lone pairs and their relation to structural distortions and thermal conductivity.

In chemistry, stereochemically active lone pairs are typically described as an important non-bonding effect, and recent interest has centred on understanding the derived effect of lone pair expression on physical properties such as thermal conductivity. To manipulate such properties, it is essential to understand the conditions that lead to lone pair expression and provide a quantitative chemical description of their identity to allow comparison between systems. Here, density functional theory calculations are used first to establish the presence of stereochemically active lone pairs on antimony in the archetypical chalcogenide MnSb2O4. The lone pairs are formed through a similar mechanism to those in binary post-transition metal compounds in an oxidation state of two less than their main group number [e.g. Pb(II) and Sb(III)], where the degree of orbital interaction (covalency) determines the expression of the lone pair. In MnSb2O4 the Sb lone pairs interact through a void space in the crystal structure, and their their mutual repulsion is minimized by introducing a deflection angle. This angle increases significantly with decreasing Sb-Sb distance introduced by simulating high pressure, thus showing the highly destabilizing nature of the lone pair interactions. Analysis of the chemical bonding in MnSb2O4 shows that it is dominated by polar covalent interactions with significant contributions both from charge accumulation in the bonding regions and from charge transfer. A database search of related ternary chalcogenide structures shows that, for structures with a lone pair (SbX 3 units), the degree of lone pair expression is largely determined by whether the antimony-chalcogen units are connected or not, suggesting a cooperative effect. Isolated SbX 3 units have larger X-Sb-X bond angles and therefore weaker lone pair expression than connected units. Since increased lone pair expression is equivalent to an increased orbital interaction (covalent bonding), which typically leads to increased heat conduction, this can explain the previously established correlation between larger bond angles and lower thermal conductivity. Thus, it appears that for these chalcogenides, lone pair expression and thermal conductivity may be related through the degree of covalency of the system.

Corrosion of Late- and Post-Transition Metals into Metal–Organic Chalcogenolates and Implications for Nanodevice Architectures

Metal chalcogenide compounds have attracted interest as materials for next generation semiconductors, catalysts, and device architectures. Hybrid compounds containing both a metal chalcogenide arch...

On the spectroscopy of Bi3+ in d10 post-transition metal oxides

The optical spectroscopy of Bi3+ in d10-based post transition metal oxides (i. e. gallates, germanates, antimonates indates, stannates) is reviewed and analyzed in the frame of empirical models. 20 different compounds are examined. From this, a methodology is introduced to identify the preferred doping sites for Bi3+ and predict the intra- or extra-ionic origin of the Bi3+ emission in these systems. Further, the emission process in calcite-structured InBO3:Bi and GaBO3:Bi is reconsidered.

Effect of microalloying with transition and post-transition metals on the aging of precipitation-hardened Al–Cu alloys

An effective alloying system for providing improved mechanical and technological properties of model cast Al–Cu alloys (Al-4.6%Cu-0.4%Mn-0.2%Ti), using magnetohydrodynamic (MHD) melt mixing, has been chosen in this research. It was shown that MHD treatment provides a non-dendritic (globular) ingot structure and can be applied to ensure thixotropy in the mass production of high-precision cast parts. Small additives of alloying elements that modify both grain structure (Mn, Zr) and reinforcing phases (Sn, In, Sc) were used. It is shown that the most effective alloying elements which improved the strength characteristics of the alloy are Sn and In. The introduction of 0.1–0.2% Sn or In followed by heat treatment led to a 50% increase in its yield strength, a 15% increase in the tensile strength. Sn and In modified the decomposition kinetics, providing a high density of precipitate and slow coalescence of nano-sized particles of the strengthening θ′-phase, which resulted in higher strength characteristics of the alloy.

Comparative analysis of transition and post transition metal mediated Allamanda cathartica L latex nanoparticles on human peripheral blood mononuclear cells

The green nanoparticles (NPs) are widely accepted as their synthesis is inexpensive and eco-friendly. In the present study, this approach was applied to synthesise nanoscale particles with transition (copper and zinc) and post-transition (iron) metals and aqueous latex of Allamanda cathartica. The selected metals are safe for human use. The experiments were carried out on human peripheral blood mononuclear cells (hPBMCs) isolated from leftover blood sample collected from diagnostic laboratory. The ratio of latex and metal solutions used to prepare NPs was 3% and 1 millimolar respectively. Ultraviolet-visible, Fourier transmission infra-red, scanning and transmission electron microscopy techniques were used to characterise the NPs. The particles were spherical, hexagonal, aggregated and rectangular and the diameter was ranged from 20.5 to 38.6 nm (zinc oxide), 17.9 to 59.2 nm (copper chloride), 29.2 to 55.4 nm (iron sulphate). Fragmentation and/or shearing took place with all the metal NPs, but clear DNA ladder pattern appeared when hPBMCs were treated with latex ZnO NPs. The order of dead cell percentage was CuCl2 (86%) > FeSO4 (87%) > ZnO (95%) after 72 h of treatment with a concentration of 100 μg. These findings indicate that the synthesised NPs are selectively damaging the DNA. Further studies need to be carried out on cancer cell lines to control the cell proliferation.

Forming indium-carbon (In–C) bonds at the edges of graphitic nanoplatelets

Indium (In), one of the soft and malleable post-transition metals, was introduced along the broken edges of graphitic nanoplatelets (GnPs) by mechanochemically ball-milling graphite in the presence of solid state In beads. After completely leaching off unreacted In using royal water (aqua regia), the formation of In–C bonds in the resulting In-doped graphitic nanoplatelets (InGnPs) was confirmed using various analytical techniques, including atomic-resolution transmission electron microscopy (AR-TEM). Scanning TEM (STEM) image shows that In elements instead of In clusters were uniformly distributed in the InGnPs, suggesting the formation of In–C bonds. The content of In in the InGnPs was 0.34 at% (3.01 wt%), as determined by X-ray photoelectron spectroscopy (XPS). The mechanochemically induced chemical reaction was powerful enough to form In–C bonds. Further, the InGnPs demonstrated catalytic activity toward the oxygen reduction reaction (ORR) comparable to commercial Pt/C catalysts, as well as excellent durability and tolerance against impurities (methanol and CO) in alkaline medium.

Efficient Conversion of CO2to Formate Using Inexpensive and Easily Prepared Post-Transition Metal Alloy Catalysts

Developing affordable electrocatalysts to facilitate the reduction of carbon dioxide (CO2) to high-value products with high selectivity, efficiency, and large current densities is a critical step f...

Nickel - p-block metal mixed chalcogenides based on AuCu3-type fragments: iodine-assisted synthesis as a way of obtaining new structures.

Two new mixed nickel-gallium chalcogenides, Ni9.39Ga2S2 and Ni5.80GaTe2, and a new mixed nickel-indium telluride, Ni5.78InTe2, have been synthesized by a high-temperature ampoule route with the addition of iodine, and characterized from single-crystal or powder diffraction data. They belong to the relatively uncommon Ni7-xMQ2/Ni10-xM2Q2 type of structures (M = Ge, Sn, Sb, In), and are built from p-block metal-centered nickel cuboctahedra, alternating along the c axis with defective Cu2Sb-type nickel-chalcogen ones. Both tellurium-containing compounds show a small degree of orthorhombic distortion with respect to the idealized tetragonal structure, only detectable in the powder diffraction data. No phase transition to the tetragonal structure was detected for Ni5.80GaTe2 by the in situ powder diffraction measurements from room temperature to 550 °C. DFT calculations show close relationships of electronic structures of these ternary compounds to their parent intermetallics, Ni3M (M = Ga, In). Metallic conductivity and paramagnetic properties are predicted for all three with the latter confirmed by magnetic measurements. The bonding patterns, investigated via the ELF topological analysis, show multi-centered nickel - p-block metal bonds in the AuCu3-type fragments and pairwise covalent interactions in the nickel-chalcogen fragments. Both Ni7-xMTe2 compounds showed no structural or compositional changes upon high-temperature mid-pressure hydrogenation.

Are There Any Overlooked Catalysts for Electrochemical NH <sub>3</sub> Synthesis? – New Insights from the Analysis of Thermochemical Data

Standard enthalpies and entropies of formation of many metal nitrides (MN) were measured in 60s, 70s and 80s of the last century. We have used this available thermochemical data and made a unique analysis in the NH3 electrocatalysis field. Briefly, we have calculated M→MN and MN→NH3 standard cell potentials for 36 metal nitrides. We found that potentials needed to start the onset for nitrogen reduction reaction (NRR), earlier calculated using density functional theory, scale linearly with the cell potentials we calculated. We have used the linear relations as “calibration curves” and from known cell potentials calculated NRR onset potentials for all elements analysed. This allowed us to build a large Volcano plot for NRR. We found that: i) transition metal Mn is the most reactive catalyst; ii) there is a gap of unidentified materials close to the top of the Volcano plot; and iii) posttransition metals, Ga and In, are close to the top. We have calculated the potentials needed to start the onset for HER and NRR at different pH and we have identified new, overlooked metal catalysts which might selectively catalyse NRR at pH>4.

High-throughput HSE study on the doping effect in anatase TiO2.

Titania is a widely used semiconductor due to its excellent optoelectronics and catalytic properties. Doping with other cations or anions by substitution of Ti or O is a common way to adjust the electronic structure of pristine TiO2. Here, using ab initio calculations at the Heyd-Scuseria-Ernzerhof (HSE06) level, the substitution energy, formation energy and electronic structures of anatase TiO2 doped with 40 kinds of elements including transition metals, alkali metals, alkaline earth metals, p-block metals, and nonmetals have been studied systematically. It is found that doping with most of these elements can narrow down the band gap of TiO2, while in some doped systems, a recombination center induced by intermediate bands is also observed. Besides, for transition metal-doped TiO2 systems, the electron spin state analysis of dopants and the doping level investigation reveal that a relatively high spin structure tends to be formed in Cr, Mn, Fe, Zn, Mo, Tc, Ru and Cd-doped TiO2, and the doping levels of 4d-orbital transition metals are generally higher than those of 3d-orbital transition metals.

Doping Effect of Lead(II) on Structural and Optical Properties of Chromium Oxide Nanoparticles

In this work, the effects of doping post transition metal (Pb2+) on the structural, morphological, elemental and optical properties of pure chromium oxide nanoparticles are reported. The structural and morphological properties were examined by X-ray diffraction and scanning electron microscopy (SEM). The elemental composition of the prepared nanoparticles were estimated from energy dispersive X-ray (EDX) absorption spectra. The band gap energies of the prepared nanoparticles (4.72-3.78 eV) obtained from UV-vis absorption spectroscopy is higher than that of bulk Cr2O3 (3.3 eV), which ensures that the prepared nanoparticles were successfully synthesized in the nano-region.

CO2 reduction on p-block metal oxide overlayers on metal substrates—2D MgO as a prototype

Recently, two-dimensional (2D) metal oxide films with a thickness of one to a few atomic layers have been grown on metal substrates, which are naturally resistant to oxidation and possess highly tunable surface properties.

Reversible OH-bond activation and amphoterism by metal-ligand cooperativity of calix[4]pyrrolato aluminate.

Most p-block metal amides irreversibly react with metal alkoxides when subjected to alcohols, making reversible transformations with OH-substrates a challenging task. Herein, we describe how the combination of a Lewis acidic square-planar-coordinated aluminum(iii) center with metal–ligand cooperativity leverages unconventional reactivity toward protic substrates. Calix[4]pyrrolato aluminate performs OH-bond activation of primary, secondary, and tertiary aliphatic and aromatic alcohols, which can be fully reversed under reduced pressure. The products exhibit a new form of metal–ligand cooperative amphoterism and undergo counterintuitive substitution reactions of a polar covalent Al–O bond by a dative Al–N bond. A comprehensive mechanistic picture of all processes is buttressed by isolation of intermediates, spectroscopy, and computation. This study delineates how structural constraints can invert thermodynamics for seemingly simple addition reactions and invert common trends in bond energies.