Reversible and irreversible colossal barocaloric effects in plastic crystals

Abstract

Colossal barocaloric effects were observed in four species of plastic crystals, and two displayed the reversibility required for cooling devices.

Reversible barocaloric effects over a large temperature span in fullerite C60

“…Above this threshold pressure change, ∆S rev (T, p atm ↔ p) is determined as the overlap between ∆S(T ) on compression and ∆S(T ) on decompression. Using the procedure described elsewhere 5 we obtain that for fullerite C 60 across its sc→fcc transition, p ∆S rev = 0 and p ∆T rev = 0.02 ± 0.01 GPa. Fig.…”

“…at first-order phase transitions because the mentioned thermodynamic changes can be large, driving the exchange of the transition latent heat. However, first-order transitions are affected by hysteresis, which can dramatically degrade the caloric performance because, on the one hand, it increases the required input work to drive the changes cyclically forth and back with the consequent decrease in efficiency, and because, on the other hand, it reduces the temperature range of operation [5][6][7] . Although strategies have been proposed 8 to take advantage of hysteresis in specific cases, in general a relatively small hysteresis is required in any solidstate caloric material to be actually suitable for implementation in future devices.…”

“…Very recently, crystals exhibiting strong orientational disorder (plastic crystals) have been identified as compounds with the largest caloric effects achieved so far in the solid state, comparable to current fluid refrigerants 21,22 . However, some are shadowed by a considerable transition hysteresis which may disqualify them for applications 5 .…”

Near-room-temperature reversible giant barocaloric effects in [(CH3)4N]Mn[N3]3 hybrid perovskite

“…With this motivation, a number of materials families have been investigated for barocaloric applications, which include magnetic alloys, [4][5][6][7][8][9] polymers, 10 oxyflourides, [11][12][13][14] ferroelectric oxides, 15,16 ferrielectric salts, 17 superionic conductors, 18,19 plastic crystals, [20][21][22][23] and hybrid organic-inorganic perovskites. [24][25][26] The latter have the potential to operate at hydrostatic pressures that are similar to those available in commercial compressors (r150 bar), specifically in the case of dicyanamide hybrid perovskites.…”

Giant and Reversible Barocaloric Effect in Trinuclear Spin‐Crossover Complex Fe3(bntrz)6(tcnset)6

“…The reversible ∆ S and ∆ T found for FBT are significantly larger than the (irreversible) values previously reported for other SCO compounds. [ 32 ] Compared to the recently reported colossal BCE in plastic crystals, [ 9,10,44 ] FBT exhibits lower ∆ S but about double ∆ T values. These larger ∆ T are due to the negligible hysteresis of the SCO transition.…”