Changes in the phonon density of states of Fe induced by external strain
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Changes in the phonon density of states of Fe induced by external strain Robert Meyer1,2 · Lena Scherthan1 · Tim Hochdörffer1 · Sakshath Sadashivaiah1 · Juliusz A. Wolny1 · Matthias W. Klein3 · Marek Smaga3 · Tilmann Beck3 · Volker Schünemann1 · Herbert M. Urbassek1,2 Received: 21 August 2020 / Accepted: 24 November 2020 © The Author(s) 2020
Abstract Nuclear inelastic scattering of synchrotron radiation is used to study the changes induced by external tensile strain on the phonon density of states (pDOS) of polycrystalline Fe samples. The data are interpreted with the help of dedicated atomistic simulations. The longitudinal phonon peak at around 37 meV and also the second transverse peak at 27 meV are decreased under strain. This is caused by the production of defects under strain. Also the thermodynamic properties of the pDOS demonstrate a weakening of the force constants and of the mean phonon energy under strain. Remaining differences between experiment and simulation are discussed. Keywords Nuclear inelastic scattering · Molecular dynamics · Phonon density of states · Extended defects
1 Introduction The phonon density of states (pDOS) constitutes a fundamental characteristics of a solid. Nowadays, for Fe the method of nuclear inelastic scattering (NIS) of synchrotron radiation can be used to measure this quantity [1]. This method also allows to study the changes of the pDOS in situations relevant for applications, such as in fatigue test used in materials science [2]. From the theoretical side, the pDOS of ideal crystals has been studied for long and is well understood [3]. However, real materials have defects, which render the calculation of the pDOS more complicated [4, 5]. For extended defects, such as dislocations or grain boundaries, atomistic simulations based on molecular dynamics can be used to calculate the pDOS of materials [6, 7]. * Herbert M. Urbassek [email protected]‑kl.de http://www.physik.uni-kl.de/urbassek/ 1
Physics Department, University Kaiserslautern, Erwin‑Schrödinger‑Straße, 67663 Kaiserslautern, Germany
2
Research Center OPTIMAS, University Kaiserslautern, Erwin‑Schrödinger‑Straße, 67663 Kaiserslautern, Germany
3
Department of Mechanical and Process Engineering, University Kaiserslautern, Erwin‑Schrödinger‑Straße, 67663 Kaiserslautern, Germany
Physical phenomena involving phonons are very often investigated via inelastic neutron scattering. This technique however is restricted to large sample volumes. Synchrotron based NIS is able to deliver the pDOS not only of 57 Fe containing samples but also of single micrometer-sized objects, thin films and even monolayers. This motivates the present study which paves the way for future investigations of defects and grain boundaries in micro- and possibly nano-objects. In this study, we present experimental data of the pDOS of Fe obtained by NIS. The data focus on the changes of the pDOS induced by straining an Fe sample. To analyze the data, we use molecular dynamics data of the pDOS in homogeneously strained Fe, on the basis of
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