Reversible colossal barocaloric effect dominated by disordering of organic chains in (CH3–(CH2)n−1–NH3)2MnCl4 single crystals

Abstract

Solid-state refrigeration based on the caloric effect is viewed as a promising efficient and clean refrigeration technology. Barocaloric materials were developed rapidly but have since encountered a general obstacle: the prominent caloric effect cannot be utilized reversibly under moderate pressure. Here, we report a mechanism of an emergent large, reversible barocaloric effect (BCE) under low pressure in the hybrid organic–inorganic layered perovskite (CH3–(CH2)n−1–NH3)2MnCl4 (n = 9,10), which show the reversible barocaloric entropy change as high as ΔSr ∼ 218, 230 J kg−1 K−1 at 0.08 GPa around the transition temperature (Ts ∼ 294, 311.5 K). To reveal the mechanism, single-crystal (CH3–(CH2)n−1–NH3)2MnCl4 (n = 10) was successfully synthesized, and high-resolution single-crystal X-ray diffraction (SC-XRD) was carried out. Then, the underlying mechanism was determined by combining infrared (IR) spectroscopy and density function theory (DFT) calculations. The colossal reversible BCE and the very small hysteresis of 2.6 K (0.1 K/min) and 4.0 K (1 K/min) are closely related to the specific hybrid organic–inorganic structure and single-crystal nature. The drastic transformation of organic chains confined to the metallic frame from ordered rigidity to disordered flexibility is responsible for the large phase-transition entropy comparable to the melting entropy of organic chains. This study provides new insights into the design of novel barocaloric materials by utilizing the advantages of specific organic–inorganic hybrid characteristics.

Low pressure reversibly driving colossal barocaloric effect in two-dimensional vdW alkylammonium halides

“…Leveraging the 2D character, there forms the phase transition during which interlayer vdW interactions get significantly weakened and interlayer spacing significantly enlarges, hence drastic orientational disorder of partial group emerges in long ((CH 3 –(CH 2 ) 9 ) 2 NH 2 ) + chains, i.e., conformational disorder of organic chains; consequently, the colossal entropy change and large volume change of phase transition can be realized altogether. Also, the interlayer weak vdW force-related 2D structural feature is deduced to induce low energy barrier of phase transition and consequently low hysteresis, for instance the hysteresis lower than 10 K in present dialkylammonium halide system and the hysteresis lower than 5 K in hybrid organic–inorganic layered perovskites 28 , 29 . Therefore, the combination of large entropy change, large volume change-related high pressure-sensitivity and weak vdW force-related low hysteresis of phase transition contributes to the enhanced reversibility of BCE meanwhile maintaining the advantage of colossal thermal effect in 3D plastic crystals, accomplishing the colossal reversible BCE driven by low pressure in 2D vdW alkylammonium halides.…”

Structure and thermal property relationships in the thermomaterial di-n-butylammonium tetrafluoroborate for multipurpose cooling and cold-storage

“…In the recent years, barocaloric materials have been demonstrated to exhibit very large thermal changes, some of them as large as Δ S ≥ 100 J K −1 kg −1 (the same order of magnitude as refrigerant gases) under the application of low/moderate pressures of p = 70–1000 bar (while refrigerant gases normally operate at p ≤ 150 bar). 17–34 These barocaloric materials belong to many different families of compounds, such as ammonium or phosphate salts, 35–43 superionic conductors, 44,45 spin crossover materials, 46–52 n -alkanes, 53 hybrid organic–inorganic materials, 54–61 organic plastic crystals 62–69 and polymers. 70–72 Even more recently, barocaloric effects have been combined with gas adsorption/desorption processes in solid-to-solid breathing-transitions in MOFs, giving rise to larger thermal changes of Δ S ∼ 300 J K −1 kg −1 under pressures as small as p ≤ 16 bar.…”

Colossal Barocaloric Effect of Binary Fatty Acid Methyl Esters under Low Pressures near Room Temperature

“…As a material changes its states (solid, liquid, and gas) under external conditions, it undergoes a significant configurational change that generates a dramatic entropy change . Unlike other caloric effects, the BC effect is not system-selective as observed in a variety of materials such as hybrid organic–inorganic material, plastic crystals, ferroelastics, etc. Therefore, the BC effect can be produced whenever a phase transition occurs.…”