Colossal barocaloric effects near room temperature in plastic crystals of neopentylglycol

Abstract

There is currently great interest in replacing the harmful volatile hydrofluorocarbon fluids used in refrigeration and air-conditioning with solid materials that display magnetocaloric, electrocaloric or mechanocaloric effects. However, the field-driven thermal changes in all of these caloric materials fall short with respect to their fluid counterparts. Here we show that plastic crystals of neopentylglycol (CH 3 ) 2 C(CH 2 OH) 2 display extremely large pressure-driven thermal changes near room temperature due to molecular reconfiguration, that these changes outperform those observed in any type of caloric material, and that these changes are comparable with those exploited commercially in hydrofluorocarbons. Our discovery of colossal barocaloric effects in a plastic crystal should bring barocaloric materials to the forefront of research and development in order to achieve safe environmentally friendly cooling without compromising performance.

Extraordinarily Large Electrocaloric Strength of Metal‐Free Perovskites

“…The barocaloric effect is defined as the temperature change induced by a change in pressure under the adiabatic condition, or by the entropy change per unit of pressure change under the isothermal condition . It is shown that the barocaloric strength of MDABCO is superior to oxide perovskite ferroelectrics such as BaTiO 3 and PbTiO 3 , but inferior to recently studied plastic crystals . One possible reason is the intermediate hardness of MDABCO between the softer plastic crystals and the harder oxide perovskite ferroelectrics.…”

Novel mechanocaloric materials for solid-state cooling applications

“…In Table 3, we enclose some of the most representative BC compounds along with some basic refrigerant characteristics. To date, giant BC effects have been measured in a number of organic-inorganic hybrid perovskites [99,100], shape-memory alloys [115][116][117], polar compounds [118,119], the archetypal fast-ion conductor AgI [120], fluoride-based materials [121], polymers [122], and molecular crystals [123][124][125][126]. The phase transitions leading to the giant BC effects reported in Table 3 present some similarities to those explained in preceding sections, made the exception of molecular crystals.…”

“…The barocaloric strengths and giant adiabatic temperature changes measured in molecular crystals, reported within the last few years, are very impressive. For instance, the |ΔT(qd)| obtained in neopentylglycol, with chemical formula (CH3)2C(CH2OH)2 [1,123,124], amounts to 45-50 K near room temperature, which actually deserves the adjective "colossal". On the other hand, the ΔT/ΔP values reported in the magnetic compounds [Fe(pzt)6](PF6)2 [125] and [FeL2][BF4]2 [126] are superior to those achieved in the rest materials listed in Table 3, made the exception of the hybrid perovskites [TPrA][Mn(dca)3] (although their corresponding operating temperatures probably are too low).…”

“…By means of external pressure it is possible to stop such molecules rotations, hence inducing a fully ordered state with low entropy. Very recently, it has been shown by several independent research groups [123,124] that the entropy changes driven by pressure near 300 K in plastic crystals are huge and render colossal BC effects (see (CH3)2C(CH2OH)2 in Table 3). It is worth mentioning that similar σ-induced caloric mechanisms were predicted previously in CH3NH3PbI3 based on the outcomes of classical molecular dynamics simulations [73] (Section 4.4).…”

“…Nevertheless, the operating temperatures associated with some ferroelectrics and fastion conductors normally are well above or below room temperature, which suggests the use of additional doping strategies in order to shift the corresponding transition temperatures. Meanwhile, colossal mechanocaloric effects (ΔT ~ 50 K near room temperature for small hydrostatic pressures of ~ 0.1 GPa [123,124]) have been discovered very recently in a class of molecular solids known as plastic crystals (e.g., neopentylglycol), which are also related to pressure-driven order-disorder phase transitions (it remains to be demonstrated whether analogous elastocaloric effects exist also in such materials). Interestingly, other types of molecular solids like organic-inorganic hybrid perovskites and spin-crossover complexes have been reported to exhibit also giant mechanocaloric effects in the last few years.…”