Atomic-scale tunable phonon transport at tailored grain boundaries and Their Impact on Thermal Conductivity

TL;DR

This study uses atomic-resolution vibrational spectroscopy to understand how specific grain boundary geometries in crystalline solids influence phonon behavior and thermal conductivity, revealing regimes of tunable thermal transport.

Contribution

It provides a detailed atomic-level correlation between grain boundary structure, vibrational states, and thermal transport, introducing a predictive framework for thermal engineering.

Findings

Low-angle tilt GBs significantly modulate thermal conductivity.

High-angle tilt GBs show saturated structural disorder with weak conductivity change.

Twist GBs locally tailor phonon transport through defect motifs.

Abstract

Grain boundaries (GBs) strongly influence thermal transport in crystalline solids by disrupting lattice periodicity and scattering phonons. Due to the atomic-level disorder and structural complexity, a fundamental understanding of how specific GB geometries regulate nanoscale phonon behavior and macroscopic thermal conductivity has remained elusive. Here, using emerging atomic-resolution vibrational spectroscopy, we directly correlate GB structure, defect-specific vibrational states, and thermal transport in bicrystal strontium titanate with controlled tilt and twist angles. The phonon characterizations and thermal conductivity data reveal two distinct regimes, where low-angle tilt GBs (2deg, 6deg, 10deg) substantially modulate phonon populations and mode frequencies, resulting in pronounced changes in thermal conductivity, whereas high-angle tilt GBs (22deg, 36deg) exhibit weak conductivity variation due to saturated structural disorder and scattering. In contrast, twist GBs introduce periodic defect motifs that only locally tailor phonon transport. Our results suggest tilt and twist angles as complementary knobs for coarse and fine control of phonon propagation and cross-GB thermal transport, providing a predictive framework for thermal engineering in materials.