Solid-state refrigeration based on caloric effects is an energetically efficient and environmentally friendly technology, which is deemed as a potential alternative to the conventional vapor-compression technology. One of the greatest obstacles to the real application is the huge driving fields. Here, we report a giant barocaloric effect in inorganic NH4I with maximum entropy changes of {\Delta}S_BCE^max ~89 J K-1 kg-1 around room temperature, associated with the orientationally order-disorder phase transition. The phase transition temperature, Tt, varies dramatically with pressure in a rate of dTt/dP ~0.81 K MPa-1, which leads to a very much small saturation driving pressure of {\Delta}P ~20 MPa, an unprecedentedly large caloric strength of |{\Delta}S_BCE^max/{\Delta}P| ~4.45 J K-1 kg-1 MPa-1, as well as a broad temperature window of ~68 K under an 80 MPa driving pressure. Comprehensive characterization of the crystal structure and dynamics by neutron scattering measurements reveals a strong reorientation-vibration coupling that is responsible for the large pressure sensitivity of Tt. This work is expected to advance the practical application of barocaloric refrigeration.

Ultrasensitive barocaloric material for room-temperature solid-state refrigeration.

The magnetocaloric effect (MCE) has been extensively studied in various magnetic solids, aiming to both facilitate practical applications in magnetic cooling and deepen our understanding these materials' intrinsic properties. This study presents a systematic investigation of Gd2Ti2O7 oxide, characterized by a geometrically frustrated magnetic structure, focusing on its structural and magnetic characteristics through experimental analysis and theoretical calculations. Emphasis is placed on its magnetic phase transition (MPT) and magnetocaloric properties, scrutinizing temperatures as low as 0.4 K and magnetic fields up to 16 T. The results reveal that Gd2Ti2O7 oxide possesses a crystalline cubic pyrochlore-type structure with an antiferromagnetic (AFM) semiconductor ground state. The material undergoes a first-order MPT in low field and low-temperature regimes, transitioning to a second-order MPT above 2 K up to 16 T. Evaluation of magnetocaloric parameters, including maximum magnetic entropy change, temperature-averaged entropy change, relative cooling power, and refrigerant capacity, indicates moderate values under low magnetic field changes, while significantly large values are achievable under high magnetic field changes. This finding suggests that potential cryogenic magnetocaloric materials (MCMs) with optimal performance should exhibit low MPT temperatures induced by magnetic frustration and possess a ground state with a sufficiently large magnetic moment induced by low magnetic fields, thus avoiding excessively strong AFM coupling. This study lays the groundwork for future cryogenic MCM design and provides valuable insights into the intrinsic properties of geometrically frustrated magnetic materials. 

Geometrically frustrated Gd2Ti2O7 oxide: A comprehensive exploration of structural, magnetic, and magnetocaloric properties for cryogenic magnetic cooling applications

Barocaloric is the more recent among the caloric technologies employing solid-state materials. The name derives from BaroCaloric Effect (BCE), the phenomenon responsible of changes in the material temperature following an adiabatic variation of the value of the applied hydrostatic pressure. Barocaloric is the technology for refrigerating and air conditions that lately earned the scene among the other caloric ones. Specifically, in the last 6 years the caloric route was turned towards barocaloric, with the consequence that it has an embryonic state, yet. The reason for such attraction lies in the promising giant temperature changes due to BCE exhibited by a wide number of materials in room temperature range. The present would be the first general review on barocaloric technology touching all the aspects of the related state of the art from a general point of view: the thermodynamic cycles, materials, numerical models, experimental devices and future perspectives. 

Cooling Through Barocaloric Effect: A Review of the State of the Art Up To 2022

Cryogenic magnetic cooling based on the principle of the magnetocaloric effects (MCEs) of magnetic solids has been recognized as an alternative cooling technology due to its significant economic and social benefits. Designing novel magnetic materials with good magnetocaloric performance is a prerequisite for practical applications. In this study, three gadolinium-transition metal-based high entropy oxides (HEOs) of Gd(Fe1/4Ni1/4Al1/4Cr1/4)O3, Gd(Fe1/5Ni1/5Al1/5Cr1/5Co1/5)O3, and Gd(Fe1/6Ni1/6Al1/6Cr1/6Co1/6Mn1/6)O3 were designed and systematically characterized regarding their structural and cryogenic magnetic properties. These HEOs were confirmed to crystallize into a single-phase perovskite-type orthorhombic structure with a homogeneous microstructure, reveal a second-order magnetic transition at low temperatures, and exhibit significant cryogenic MCEs. The magnetocaloric performances of the present HEOs, identified by magnetic entropy changes, relative cooling power, and temperature-averaged entropy changes, were comparable with recently reported candidate materials. The present study indicates potential applications for cryogenic magnetic cooling of the present HEOs and provides meaningful clues for designing and exploring HEOs with good cryogenic magnetocaloric performances. 

Designing gadolinium-transition metals-based perovskite type high entropy oxides with good cryogenic magnetocaloric performances

Investigation of the structural and magnetic properties of the GdCoC compound featuring excellent cryogenic magnetocaloric performance

The discovery of colossal barocaloric effects in organic plastic crystals has significantly advanced the development of solid‐state refrigerant techniques. Adapting to the real application, a tradeoff of various barocaloric performances has to be achieved. Here, it is reported a novel plastic crystal system, that is, carboranes (C2B10H12), including three positional isomers: ortho‐carborane, meta‐carborane, and para‐carborane, which are characterized by C2v, C2v, D5d point groups, respectively. They all undergo an orthorhombic‐to‐tetragonal phase transition around room temperature. Compared to the previously reported organic plastic crystals, this system exhibits a combination of large pressure‐normalized entropy changes, the high‐pressure sensitivity of the transition temperature, small thermal hysteresis, and so forth. Their barocaloric performances are positional‐isomerism dependent, and the best performances are obtained in para‐carborane with maximum entropy changes of about 106.2 J kg−1 K−1 achieved under pressure changes below 30 MPa. This study not only suggests that carboranes would be a considerably promising working material for barocaloric refrigeration at room temperature but also indicates that delicate tuning of molecular isomerism is an effective strategy to enhance barocaloric performances.

Colossal Barocaloric Effect in Carboranes as a Performance Tradeoff

Ultralow-field magnetocaloric materials for compact magnetic refrigeration

The senescence of mesenchymal stem cells (MSCs) impairs their regenerative capacity to maintain tissue homeostasis. Numerous studies are focusing on the interventions and mechanisms to attenuate the senescence of MSCs. C-phycocyanin (C-PC) is reported to have multiple functions such as antitumor, antioxidation, anti-inflammation and anti-aging roles, but there is little research about the effects of C-PC on the senescence of MSCs. Here we investigated the roles and mechanism of C-PC on MSCs senescence. In vitro results showed that C-PC could reduce senescence, enhance proliferation, promote the adipogenic and osteogenic differentiation in senescent MSCs induced by oxidative stress. In vivo D-Galactose (D-Gal) induced rats aging models showed C-PC also increased the viability and differentiation of intrinsic senescent bone marrow derived MSCs (BMSCs). Furthermore, C-PC also decreased the levels of oxidative stress markers ROS or MDA, elevated the SOD activity, and increased the anti-inflammatory factors. Proteomic chip analysis showed that C-PC interacted with ZDHHC5, and their interaction was verified by pull down assay. Overexpression of ZDHHC5 aggravated the senescence of MSCs and greatly lessened the beneficial effects of C-PC on senescence. In addition, we found ZDHHC5 regulated autophagy by altering LC3, Beclin1 and PI3K/AKT/mTOR pathway. In summary, our data indicated that C-PC ameliorates the senescence of MSCs through zinc finger Asp-His-His-Cys (DHHC) domain-containing protein 5 (ZDHHC5) mediated autophagy via PI3K/AKT/mTOR pathway. The present study uncovered the key role of autophagy in MSCs senescence and PI3K/AKT/mTOR pathway may be a potential target for anti-senescence studies of MSCs.

C-Phycocyanin Ameliorates the Senescence of Mesenchymal Stem Cells through ZDHHC5-Mediated Autophagy via PI3K/AKT/mTOR Pathway.

A large driving pressure is required for barocaloric effects (BCEs) in intermetallics, usually above 100 MPa. Here, we report barocaloric effects in Mn3-xPt1+xalloys saturated at about 60 MPa, the lowest pressure reported in intermetallics to date. A first-order phase transition occurs from the colinear antiferromagnetic phase to the triangular antiferromagnetic phase as temperature decreases. The transition temperature strongly depends on the composition x, ranging from 331 K for x = 0.18 to 384 K for x = 0.04, and is sensitive to pressure, with dTt/dP up to 139 K/GPa. However, the maximum pressure-induced entropy changes are as small as 13.79 J kg-1 K-1, attributed to the mutual cancellation of lattice and magnetic entropy changes. The small driving pressure and total entropy changes are due to the special magnetic geometric frustration.

https://doi.org/10.20517/microstructures.2022.46

Low-pressure-driven barocaloric effects at colinear-to-triangular antiferromagnetic transitions in Mn3-xPt1+x

AgCrSe2, a quasi-two-dimensional material, is famous for its superionic conducting. Here, it is confirmed that the anisotropic behaviors exist in the magnetic, electronic, and magneto-transport properties of the AgCrSe2 single crystal. A field induced phase transition causes asymmetrical antiferromagnetic states in the μ0 H//ab plane and the c axis, which correspond to the positive/negative magnetoresistances in two directions, respectively. Below ∼32 K, a spin flop is manifested with a magnetic field of about 4 T, according to the field dependent electoral resistance. The anisotropic behaviors are ascribed to the quasi-two-dimensional structure and also to the unstable Ag+ ions and the puckered honeycomb lattice of Cr3+ ions. This research reveals fundamental transport properties in AgCrSe2 single crystals and can be explored further in superionic conductor engineering.

Anisotropic magnetoelectric transport in AgCrSe2 single crystals

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