All-temperature barocaloric effects at pressure-induced phase transitions.

Area of Science:

• Solid-state physics
• Materials science
• Thermodynamics

Background:

• Caloric effects are crucial for solid-state refrigeration but are typically limited by narrow temperature spans.
• Existing technologies often require multi-stage systems to achieve desired cooling ranges.

Purpose of the Study:

• To introduce and demonstrate an all-temperature barocaloric effect for advanced solid-state refrigeration.
• To investigate the underlying mechanisms of this effect in KPF$_{6}$ across a broad temperature spectrum.

Main Methods:

• Experimental measurement of barocaloric adiabatic temperature change under pressure.
• Pressure-dependent neutron powder diffraction and Raman scattering analyses.
• First-principles calculations and thermodynamic energy landscape depiction.

Main Results:

• Demonstrated a significant barocaloric effect in KPF$_{6}$ from 77.5 K to 300 K, with potential down to 4 K.
• Achieved adiabatic temperature changes of 12 K at room temperature and 2.5 K at 77.5 K under 250 MPa pressure.
• Identified a persistent phase transition to a rhombohedral high-pressure phase as the cause.

Conclusions:

• The all-temperature barocaloric effect in KPF$_{6}$ offers a groundbreaking solution for versatile solid-state refrigeration.
• This discovery transcends limitations of conventional refrigeration, paving the way for highly applicable technologies.
• Understanding the thermodynamic energy landscape explains the observed structural instability and effect.