Theoretical investigations of electrical transport properties in CoSb3 skutterudites under hydrostatic loadings

CoSb3-based mark mid-temperature skutterudites have been a benchthermoelectric material under intensive experimental and theoretical studies for decades. Doping and filling, to the first order, alter the crystal lattice constant of CoSb3 in the context of ＂chemical pressure.＂ In this work, we employed ab initio density functional theory in conjunction with semiclassical Boltzmann transport theory to investigate the mechanical properties and especially how hydrostatic loadings, i.e., ＂physical pressure,＂ impact the electronic band structure, Seebeck coefficient, and power factor of pristine CoSb3. It is found that hydrostatic pressure enlarges the band gap, suppresses the density of states （DOS） near the valence band edge, and fosters the band convergence between the valley bands and the conduction band minimum （CBM）. By contrast, hydrostatic tensile reduces the band gap, increases the DOS near the valence band edge, and diminishes the valley bands near the CBM. Therefore, applying hydrostatic pressure provides an alternative avenue for achieving band convergence to improve thermoelectric properties of N-type CoSb3, which is further supported by our carrier concentration studies. These results provide valuable insight into the further improvement of thermoelectric performance of CoSb3-based skutterudites via a synergy of physical and chemical pressures.

Atomistic observation of in situ fractured surfaces at a V-doped WC–Co interface

1.Introduction Cemented carbides are composites of WC ceramic phases and metallic Co binders that endow them with superior hardness and excellent toughness.Hard metals are widely used as metal cutting and rock drilling tools[1,2].Their hardness is believed to be inversely proportional to the sizes of WC grains^([3]).Grain growth inhibitors are widely employed to achieve smaller grain sizes.

Computing grain boundary diagrams of thermodynamic and mechanical properties

Computing the grain boundary(GB)counterparts to bulk phase diagrams represents an emerging research direction.Using a classical embrittlement model system Ga-doped Al alloy,this study demonstrates the feasibility of computing temperature-and composition-dependent GB diagrams to represent not only equilibrium thermodynamic and structural characters,but also mechanical properties.Specifically,hybrid Monte Carlo and molecular dynamics(MC/MD)simulations are used to obtain the equilibrium GB structure as a function of temperature and composition.Simulated GB structures are validated by aberrationcorrected scanning transmission electron microscopy.Subsequently,MD tensile tests are performed on the simulated equilibrium GB structures.GB diagrams are computed for not only GB adsorption and structural disorder,but also interfacial structural and chemical widths,MD ultimate tensile strength,and MD tensile toughness.This study suggests a research direction to investigate GB composition–structure–property relationships via computing GB diagrams of thermodynamic,structural,and mechanical(or potentially other)properties.