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| Home > Publications database > Elucidating entropy contributions of barocaloric effect in spin crossover complex Fe(PM-BiA)2(NCS)2 |
| Poster (Invited) | FZJ-2025-02979 |
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2025
Abstract: Background: The barocaloric effect (BCE) is characterized as a thermal response in solid-state materials induced by external hydrostatic pressure. Cooling technologies based on the BCE have emerged as a promising alternative to conventional vapor-compression cooling. Recently, spin crossover (SCO) transitions, where the low spin and high spin states can be switched by hydrostatic pressure, were proposed as a potential mechanism to generate outstanding BCE. Fe(PM-BiA)2(NCS)2 (with PM = N-2’- pyridylmethylene and BiA = 4-aminobiphenyl) is a classic SCO complex that crystalizes in two different structures, orthorhombic with abrupt transition and monoclinic with gradual transition. In this work, we aim to unveil the entropy contributions of Fe(PM-BiA)2(NCS)2 for optimizing the BCE performance on SCO complexes. Methods: Spectroscopic methods including nuclear inelastic scattering (NIS, P01), inelastic neutron scattering (INS, PANTHER & PELICAN) and quasi elastic scattering (QENS, PANTHER & EMU) have been used for dynamic studies of Fe(PM-BiA)2(NCS)2. Results: The dynamic features of both polymorphs over a large energy range are highlighted by spectroscopic methods. The complete and Fe-related lattice dynamics have been accessed through INS and NIS, respectively. It indicates that the Fe-related entropy change across the spin transition is around 54.6% of the total entropy change. The single crystal X-ray diffraction evidences the potential dynamic disorder of phenyl groups. A two-site reorientation mode of the phenyl group at the ps time scale has been observed by QENS. This local mode also generates 12% of the total entropy change.Conclusion: In summary, we confirm that both the phonon excitations of Fe-N octahedron and the local motions of phenyl groups play crucial roles in contributing to the total entropy change in Fe(PM-BiA)2(NCS)2. Our study will enhance the understanding of the caloric effect in the SCO complex and promote the application of SCO complexes as BCE refrigerants.
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