Spin-Crossover Transition Leads to Giant Barocaloric Effect​

February 9, 2020
Spin-Crossover Transition Leads to Giant Barocaloric Effect​
(Top): Schematic energy level diagram for an octahedrally coordinated Fe(II) ion showing the effect of a ligand field in generating a low spin (LS) or high spin (HS) state. ∆0 is the ligand field splitting energy and P is the spin-pairing energy. (Bottom)

Scientific Achievement

The pressure and temperature dependence of structure and calorimetry in the compound [FeL2][BF4]2, where L is a partially deuterated ligand (2,6-di(pyradzol-1-yl)pyridine), established the existence of a large spin-crossover driven barocaloric effect.

Significance and Impact

This is the first experimental evidence for a spin cross-over driven barocaloric effect, relating hydrostatic pressure and temperature change, relevant for solid state refrigeration.​

Research Details

  • [FeL2][BF4]2 was deuterated at the Center for Nanoscale Materials Sciences.​
  • In situ high pressure neutron diffraction measurements determined the temperature and pressure dependence of the spin crossover (SC) transition. ​
  • Calorimetric measurements were made to determine the entropy change across the SC transition.​

S.P. Vallone2, 3, A.N. Tantillo2,3, A.M. dos Santos1, J. Molaison1, R. Kulmaczewski5, A. Chapoy4, P. Ahmadi4, M.A. Halcrow5, K.G. Sandeman2, 3, ​
Advanced Materials, 31, 1807334 (2019). DOI: 10.1002/adma.201807334​