Refrigeration through Barocaloric Effect Using the Spin Crossover Complex {Fe[H₂B(pz)₂]₂(bipy)}

Abstract

Spin crossover complexes have a very striking signature of a huge volume change coupled with low–high spin conversion around a critical temperature, which can be pressure tuned in a large temperature interval. Herein, the barocaloric effect is reported in the spin crossover complex {Fe[H2B(pz)2]2(bipy)} (bipy = 2,2′‐bipyridine) from theoretical and applied points of view. The experimental data reveal a giant barocaloric effect, through the isothermal entropy change (ΔST = 83 J kg−1 K−1) around T = 273 K, upon moderated hydrostatic pressure variation (ΔP = 2 kbar). The high and linear behavior in the pressure dependence of the phase transition temperature (19 K kbar−1) leads to a huge relative cooling power (RCP = 7296 J kg−1) upon ΔP = 3 kbar, which is discussed using Ericsson's cooling cycle. Theoretical results, obtained from a microscopic model, updated with the vibration modes from density functional theory (DFT) calculation, show remarkable agreement with the experimental data.

Chemical pressure as an effective tool for tuning the structural disordering and barocaloric efficiency of complex fluorides (NH4)3MF7 (M: Sn, Ti, Ge, Si)

“…The values of ∆S BCE and ∆T AD are presented in table 2 without taking into account the temperature hysteresis. However, the actual reversible changes in the extensive and intensive BCE, which must be determined in accordance with (7) and (8), significantly depend, albeit to a different extent, on the value of δT 0 (figure 6(b)). Obviously, this effect is critical for materials with δT 0 ≫ 1 K.…”

“…This point reveals that, firstly, BCE can be realized in solids of different physical origin and, secondly, their largest values can be realized in the region of phase transitions, where the derivative (∂V/∂T) p demonstrates anomalous behavior. Such universality has recently stimulated a significant increase in interest in BCE in inorganic (ferroelastics, ferroelectrics, ferromagnets, superionic conductors, etc), organic (plastic crystals) and organic-inorganic hybrid (two-dimensional metal-halide perovskites, formamidinium iodide, etc) materials [7][8][9][10][11][12][13][14][15]. Until now, despite a lot of publications, intensive study of BCE is mainly aimed at searching for materials demonstrating 'a huge' ('unusual large', 'giant', 'colossal') extensive BCE and undergoing, as a rule, one phase transition.…”

Synergistic Advancement of Molecular Design and Dual Encapsulation Technology for High‐Performance Room‐Temperature Barocaloric Refrigeration Materials

“…Therefore, researchers have started exploring other alternative barocaloric materials with suitable refrigeration temperatures. For instance, P. J. von Ranke [23] discovered a giant barocaloric effect in Fe[H 2 B(pz) 2 ] 2 (bipy), with an entropy change (ΔS T = 83 J kg −1 K −1 ) at 273 K. Li et al [24] found a barocaloric effect in a ortho-carborance (C 2 B 10 H 12 ), with an entropy change of ≈86 J kg −1 K −1 at 275 K, and reported NH 4 I [25] as another potential barocaloric material with an entropy change of 71 J kg −1 K −1 at 268 K. However, while these materials have suitable refrigeration temperatures, their entropy change is significantly lower than that of NPG, resulting in a lower refrigeration capacity. Hence, finding a material with both a suitable refrigeration temperature and a colossal barocaloric effect remains a challenging task.…”

On the colossal barocaloric effect in higher n-alkanes

“…Different types of such materials have been studied recently and exhibit giant or colossal (or supergiant) BC effects, such as plastic crystals, 6–8 elastomeric polymers (elastomers), 9–13 organic–inorganic hybrid perovskites and metal–organic frameworks 14–17 and other coordination compounds. 18–20 Most of the BC materials studied so far present a more pronounced BC effect only around solid–solid phase transitions, while elastomers present a giant BC effect in wider temperature ranges, even in the absence of phase transitions. 9–13 Nevertheless, solid–liquid phase transitions may significantly increase the BC effects, and, consequently, the potential for application in BC-based refrigerators.…”