Non-local cooperative atomic motions that govern dissipation in amorphous tantala unveiled by dynamical mechanical spectroscopy

TL;DR

This study reveals that mechanical dissipation in amorphous tantala is driven by cooperative atomic rearrangements involving extended clusters, with low-temperature oxygen atom rearrangements correlating with increased mechanical losses.

Contribution

It uncovers the microscopic mechanisms of dissipation in amorphous tantala, highlighting the role of cooperative atomic motions and structural connectivity.

Findings

Dissipation linked to irreversible atomic rearrangements in extended clusters.

Low-temperature excess of plastically rearranging oxygen atoms correlates with mechanical loss peaks.

Rearranging polyhedra preferentially connect via edges and faces.

Abstract

The mechanisms governing mechanical dissipation in amorphous tantala are studied at microscopic scale via Molecular Dynamics simulations, namely by mechanical spectroscopy in a wide range of temperature and frequency. We find that dissipation is associated with irreversible atomic rearrangements with a sharp cooperative character, involving tens to hundreds of atoms arranged in spatially extended clusters of polyhedra. Remarkably, at low temperature we observe an excess of plastically rearranging oxygen atoms which correlates with the experimental peak in the macroscopic mechanical losses. A detailed structural analysis reveals preferential connections of the irreversibly rearranging polyhedra, corresponding to edge and face sharing. These results might lead to microscopically informed design rules for reducing mechanical losses in relevant materials for structural, optical, and sensing applications.