arXiv subjects

Maximilian A. Springer

Publications and source records attributed to Maximilian A. Springer.

4 recordsLinked to original sources

arXiv2024

Surface segregation in high-entropy alloys from alchemical machine learning

High-entropy alloys (HEAs), containing several metallic elements in near-equimolar proportions, have long been of interest for their unique mechanical properties. More recently, they have emerged as a promising platform for the development of novel heterogeneous catalysts, because of the large design space, and the synergistic effects between their components. In this work we use a machine-learning potential that can model simultaneously up to 25 transition metals to study the tendency of different elements to segregate at the surface of a HEA. We use as a starting point a potential that was previously developed using exclusively crystalline bulk phases, and show that, thanks to the physically-inspired functional form of the model, adding a much smaller number of defective configurations makes it capable of describing surface phenomena. We then present several computational studies of surface segregation, including both a simulation of a 25-element alloy, that provides a rough estimate of the relative surface propensity of the various elements, and targeted studies of CoCrFeMnNi and IrFeCoNiCu, which provide further validation of the model, and insights to guide the modeling and design of alloys for heterogeneous catalysis.

cond-mat.mtrl-sci↗

arXiv2023

Modeling high-entropy transition-metal alloys with alchemical compression

Alloys composed of several elements in roughly equimolar composition, often referred to as high-entropy alloys, have long been of interest for their thermodynamics and peculiar mechanical properties, and more recently for their potential application in catalysis. They are a considerable challenge to traditional atomistic modeling, and also to data-driven potentials that for the most part have memory footprint, computational effort and data requirements which scale poorly with the number of elements included. We apply a recently proposed scheme to compress chemical information in a lower-dimensional space, which reduces dramatically the cost of the model with negligible loss of accuracy, to build a potential that can describe 25 d-block transition metals. The model shows semi-quantitative accuracy for prototypical alloys, and is remarkably stable when extrapolating to structures outside its training set. We use this framework to study element segregation in a computational experiment that simulates an equimolar alloy of all 25 elements, mimicking the seminal experiments by Cantor et al., and use our observations on the short-range order relations between the elements to define a data-driven set of Hume-Rothery rules that can serve as guidance for alloy design. We conclude with a study of three prototypical alloys, CoCrFeMnNi, CoCrFeMoNi and IrPdPtRhRu, determining their stability and the short-range order behavior of their constituents.

cond-mat.mtrl-sci↗

arXiv2021

Electronic Structures of Two-Dimensional PC6-Type Materials

Two-dimensional (2D) materials may exhibit intriguing band structure features (e.g., Dirac points), that lay far away from the Fermi level. They are, thus, not usable in applications. The semiconducting 2D material PC6 has two Dirac cones above and below the Fermi level. Therefore, it is an ideal playground to demonstrate chemical functionalization methods for shifting the Fermi level in order to access interesting band structure features. PC6 is based on the sqrt(7) x sqrt(7)R19.1deg super cell of graphene with two carbon atoms per unit cell substituted by phosphorous. It is demonstrated how substitution with other heteroatoms that contain a different number of valence electrons, the Dirac points can be accessed. Alternatively, hydrogen atoms can be used as adatoms at the heteroatom sites. This increases electron filling and shifts the Fermi level upwards.

cond-mat.mtrl-sci↗

arXiv2021

A semimetallic square-octagon (fes) two-dimensional polymer with high mobility

The electronic properties of $π$-conjugated two-dimensional (2D) polymers near the Fermi level are determined by structural topology and chemical composition. Thus, tight-binding (TB) calculations of the corresponding fundamental network can be used to explore the parameter space to find configurations with intriguing properties before designing the the atomistic 2D polymer network. The vertex-transitive \textbf{fes} lattice, which is also called square-octagon lattice, is rich in interesting topological features including Dirac points and flat bands. Herein, we study its electronic and topological properties within the TB framework using representative parameters for chemical systems. Secondly, we demonstrate that the rational implementation of band structure features obtained from TB calculations into 2D polymers is feasible with a family of 2D polymers possessing \textbf{fes} structure. A one-to-one band structure correspondence between fundamental network and 2D polymers is found. Moreover, changing the relative length of linkers connecting the triangulene units in the 2D polymers reflect tuning of hopping parameters in the TB model. These perturbations allow to open sizeable local band gaps at various positions in the Brillouin zone. From analysis of Berry curvature flux, none of the polymers exhibits a large topologically non-trivial band gap. However, we find a particular configuration of semimetallic characteristics with separate electron and hole pockets, which possess very low effective masses both for electrons (as small as $m^*_\mathrm{e} = 0.05$) and holes (as small as $m^*_\mathrm{h} = 0.01$).

cond-mat.mtrl-sci↗