A collaborated research team from the Institute of Solid State Physics, the Hefei Institutes of Physical Science of the Chinese Academy of Sciences, has discovered a high-energy-density barocaloric effect in the plastic superionic conductor Ag₂Te₁₋ₓSₓ.
"This material shows a volumetric barocaloric performance far beyond that of most known inorganic materials," said the Prof. TONG Peng, who led the team, "Its high energy density makes it well-suited for smaller and lighter cooling devices."
The findings were published online in Advanced Functional Materials.
Modern refrigeration mainly relies on vapor-compression systems, which use greenhouse-gas refrigerants and are already near their efficiency limit. Barocaloric refrigeration—cooling by applying pressure to solid materials—offers a cleaner and potentially more efficient alternative. However, a key factor for real devices, volumetric entropy change, has not been well addressed.
Through finite element simulation, the team found that reducing the container size enhances its pressure-bearing capacity under pressure, thereby permitting a reduction in wall thickness and achieving a secondary weight reduction. This highlights the need for high-energy-density materials, yet most known barocaloric materials still fall short in this area.
In this study, the team focused on a dense solid solution, Ag₂Te₁₋ₓSₓ. Experiments showed that under a moderate pressure of only 70 MPa, the material produces a reversible volumetric entropy change of 0.478 J·cm⁻³·K⁻¹—the highest value reported for any inorganic barocaloric material so far. Its barocaloric strength, 6.82 mJ·cm⁻³·K⁻¹·MPa⁻¹, also surpasses most inorganic systems and even beats well-known organic materials such as neopentyl glycol.
Neutron diffraction data reveal what drives this unusually strong thermal response. When pressure is applied, the material undergoes a structural shift from a cubic to a monoclinic phase, accompanied by a lattice volume change of about 5.4%. At the same time, the diffusions of silver ions inside the structure changes sharply, further amplifying the caloric effect.
The material also shows several practical advantages. It conducts heat relatively well and is highly deformable, allowing it to be shaped into millimeter-scale pellets or thin sheets that can efficiently exchange heat. Even after heavy deformation, rapid temperature changes, and repeated pressure cycling, the barocaloric performance remains stable—an important sign of reliability for future solid-state cooling technologies.
This work introduces a new material platform that combines giant volumetric barocaloric effects, good mechanical processability, and relatively high thermal conductivity—offering fresh possibilities for next-generation green cooling technologies.
