Regensburg 2022 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 10: Poster Session 1

MM 10.6: Poster

Monday, September 5, 2022, 18:00–20:00, P2

Investigating the short-range order of amorphous GeTe upon structural relaxation obtained by TEM diffractometry and RMC methods — •Christian Stenz¹, Julian Pries¹, T. Wesley Surta², Michael W. Gaultois², and Matthias Wuttig¹ — ¹Institute of Physics IA, RWTH Aachen University, 52074 Aachen, Germany. — ²Faculty of Chemistry, University of Liverpool, Liverpool L7 3NY, United Kingdom.

New experimental insights into the structural changes during resistance drift in amorphous GeTe are presented. Selected area electron diffraction is performed on a-GeTe in five different annealing states to compute the pair distribution functions upon relaxation. Examination of the short-range order based on the order parameters S(q₂)/S(q₁) and r₂/r₁ implies a continuous increase in the most prominent average bond angle by 1^∘ towards 104.5^∘. This is consistent with the analysis of the bond angle distribution (RMC simulations) which reveals a shift of the main contribution (∼ 103.5^∘) towards larger angles. A concomitant increase of intermediate geometries between tetrah. and octah. (∼ 140^∘) is observed. Applying three different techniques to estimate the fraction of tetrahedral Ge atoms the three measures coherently suggest a decrease in tetrahedicity. We conclude that an enhancement of Peierls-like distorted/pyramidal motifs, i.e. an increase in the PD-ratio r_L/r_S, causes the increase of the average bond angle, resulting in a widening of the band gap. This structural relaxation ultimately leads to the resistance drift.