科研之友
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摘要
Both the barocaloric effect (BCE) and its reversible behavior during martensitic transformation (MT) have been experimentally investigated in Ni42.3Co7.9Mn38.8Sn11 quaternary Heusler alloy. The experimental results show that the studied alloy experiences the MT from the ferromagnetic L2(1)-type cubic structure to the paramagnetic-like three-layered (3M) modulated monoclinic structure, resulting in a value of similar to 1.1% for the relative volume change epsilon between two phases. Due to appearance of an enhanced epsilon, the migration rate of martensitic transformation with respect to the hydrostatic pressure reaches similar to 4.7 K/kbar, while a high transition entropy change (similar to 28 J/kg K) is still maintained. Based on an indirectly estimated method, the calculated maximumvalue for isothermal entropy change Delta S-T achieves similar to-23 J/kg K with the pressure change of 6.2 kbar, which yields the values of similar to 10 K for adiabatic temperature change Delta T-ad and similar to 786 J/kg for relative cooling power (RCP), performing a large BCE. According to the change of phase fraction at selected hydrostatic pressures, a detailed schematic diagram has been established to evaluate the reversibility of this effect. With applying an external cyclic pressure of 6.2 kbar, the maximum repeatable values calculated for both Delta S-T and Delta T-ad are decreased to similar to-15 J/kg K and similar to 5 K, respectively. This is attributed to an insufficient driving force, which can only partially transform this material, leading to a reversible MT appeared in the mixed state.
