Neutron powder diffraction and molecular dynamics study of superionic SrBr2.

Area of Science:

• Materials Science
• Solid-State Chemistry
• Crystallography

Background:

• Superionic conductors exhibit high ionic conductivity.
• Strontium bromide (SrBr2) is a unique superionic conductor featuring bromide (Br(-)) ion conduction.
• Understanding ionic disorder is crucial for designing advanced materials.

Purpose of the Study:

• To investigate the dynamic ionic disorder in the superionic phase of strontium bromide (β-SrBr2).
• To elucidate the mechanism of anion diffusion and cation-anion interactions.
• To compare the ionic disorder with the ordered phase and other superionic materials.

Main Methods:

• Neutron powder diffraction data analyzed using reverse Monte Carlo (RMC) modeling.
• Ab initio molecular dynamics (MD) simulations.
• Analysis of ionic trajectories and coordination environments.

Main Results:

• RMC and MD simulations showed good agreement, confirming extensive dynamic disorder in the Br(-) sublattice.
• Anion diffusion occurs primarily through nearest-neighbor hops along 〈100〉 directions with curved trajectories.
• Correlated Br(-) motion leads to transient square antiprism coordination around Sr(2+).

Conclusions:

• The study clarifies the nature of dynamic ionic disorder in β-SrBr2.
• Findings highlight the role of anion size in superionic conductivity.
• The observed phenomena provide insights into the behavior of superionic materials.