Strong Proton-Phonon Coupling Drives Fast Ion Transport in Perovskites

Area of Science:

• Materials Science
• Solid-State Chemistry
• Condensed Matter Physics

Background:

• Proton conduction in solids is crucial for energy applications but is complex, influenced by thermal vibrations.
• Understanding the role of lattice dynamics and phonon interactions is key to designing efficient proton conductors.

Purpose of the Study:

• To investigate the mechanism of proton transport in Y-doped BaSnO3.
• To elucidate the role of phonon modes and lattice structure in proton conductivity.
• To develop a quantitative model for predicting proton transport properties.

Main Methods:

• High-resolution neutron diffractometry for crystallographic structure determination.
• Density functional theory calculations for phonon density of states.
• Element-specific nuclear resonant vibration spectroscopy for experimental validation.
• Quantitative transport modeling based on phonon analysis.

Main Results:

• Yttrium substitution induces an imaginary phonon mode, facilitating proton transport.
• The oxygen sub-lattice momentum transfer, not individual modes, drives proton conduction.
• A quantitative model successfully predicts activation energy and performance based on ionic radii ratio.
• The model incorporates phonon-phonon interactions, extending transition state theory.

Conclusions:

• Lattice dynamics, specifically phonon properties influenced by dopants like Y, are critical for proton transport.
• The ratio of ionic radii governs momentum transfer from the oxygen sub-lattice to protons.
• The developed model provides a predictive framework for designing advanced proton conducting materials.