Incipient Ionic Conductors: Ion-Constrained Lattices Achieving Superionic-Like Thermal Conductivity Through Extreme...

Area of Science:

• Materials Science
• Solid State Physics
• Thermoelectrics

Background:

• Superionic conductors exhibit phonon liquid-like thermal conduction, making them promising for thermoelectric devices.
• However, high ion mobility in superionic conductors leads to material degradation and instability, posing a challenge for practical applications.

Purpose of the Study:

• To investigate phonon liquid-like thermal transport and ion migration in CsCu2I3 with incipient ionic conduction.
• To explore the potential of incipient ionic conductors for achieving both low thermal conductivity and high material stability.

Main Methods:

• Synchrotron X-ray diffraction
• Inelastic X-ray scattering
• Machine-learning potential-based simulations

Main Results:

• CsCu2I3 exhibits phonon liquid-like thermal transport with restricted long-range ion migration.
• Cu ions show confined migration within CuI4 tetrahedra, leading to extreme phonon anharmonicity.
• A glass-like thermal conductivity (κ ≈ 0.3 W m⁻¹ K⁻¹ at 300 K) was achieved with significantly reduced Cu ion migration compared to superionic conductors.

Conclusions:

• Incipient ionic conductors like CsCu2I3 offer a pathway to simultaneously achieve low thermal conductivity and high stability.
• Restricting ion migration is key to maintaining material integrity while leveraging phonon liquid-like transport.
• This work provides insights into thermal transport mechanisms and opens avenues for developing advanced thermoelectric materials.