Title:	Pair distribution functions in amorphous Fe-Ni-Al-Zr alloys
DNr:	NAISS 2023/5-56
Project Type:	NAISS Medium Compute
Principal Investigator:	Gabriella Andersson <gabriella.andersson@physics.uu.se>
Affiliation:	Uppsala universitet
Duration:	2023-02-23 – 2024-03-01
Classification:	10304
Keywords:

Abstract

The absence of long-range order in amorphous metals and the possibility to alloy glass forming elements in non-stoichiometric fractions enable precise fine-tuning of the composition, atomic density and separation of atomic pairs. Linking the local atomic environment to mechanical, electrical, thermodynamical and magnetic properties via first principle calculations and experimental measurements makes it possible to construct a theoretical screening method in which novel promising materials can be identified and synthesized. The aim of this project is to investigate structural aspects of amorphous metals, in particular zirconium-based alloys, to relate local distribution of atomic pairs and their environment to macroscopic properties. From a scattering point of view, the distribution of atomic pairs lays the foundation of the allowed momentum transfers in the material via its static structure factor, which is a Fourier transform of the pair distribution function (PDF). X-ray diffraction [1] and nearly-free electric transport models [2] rely on the shape and magnitude of the structure factor. By connecting these quantities to in-house measured diffraction patterns and resistivity measurements we can assess the validity of the numerically constructed amorphous systems to extend the screening method beyond the current scope of our experiments. Furthermore, the configurational information in the form of the material’s entropy is also captured in the distribution of atoms [3]. The correlation between pairs of particles limits the required knowledge to describe a closed amorphous system such that the reduction in informational entropy from an uncorrelated gaseous state describe the total configurational entropy of the state of the material. Reliable first principle calculations of entropy are thus required to enable us to examine the thermodynamics of amorphous materials on an absolute scale. To perform this study, we will first use the stochastic quenching method [4]to ab initio construct atomistic models of the amorphous systems using VASP as our choice of density functional theory (DFT) code. The method creates candidate structures via the principle of maximally amorphous materials in which a randomised supercell of atomic coordinates is let to relax to a configurational state that eventually resides in a local degenerate amorphous energy minimum, exhibiting zero local forces. The ensemble average of several such quenched structures, initialized from different random starting conditions, will reflect the distributive properties of the structure, such as the total and pair decomposed pair distribution function and the atomic bond angle distribution. Once the amorphous candidate cells have been constructed, electronic structure calculations can be conducted to research the material’s enthalpic, elastic and electronic properties. For this reason, this project will be of significant value for Sweden’s scientific competitiveness. [1] Billinge, S. J. L., Zeitschrift für Kristallographie - Crystalline Materials, vol. 219, no. 3, 2004, pp. 117-121. [2] S. R. Nagel and J. Tauc, Physical Review Letters 35, 380(1975) [3] M. C. Gao and M. Widom,The Journal of Physical Chemistry B 2018 122 (13), 3550-3555 [4] E. Holmström et al., Physical Review B 82, 024203 (2010)