Construction And Application Of Phase Transition Caloric Effect Measurement System Under Hydrostatic Pressure And Magnetic Field

Solid-state refrigeration technology is expected to become a new generation of refrigeration technology to replace traditional compression refrigeration technology due to its high efficiency,environmental protection and many other advantages in the future.In recent years,the caloric effect of pressure-driven phase transition(barocaloric effect)has attracted wide attention due to its rich material variety and excellent properties.Currently,commercial equipment for barocaloric effect testing is extremely scarce and expensive.Most of the equipment abroad is self-developed by research groups,and there is no self-made equipment in China,which restricts the further scientific research.Plenty of phase change materials are sensitive to pressure and magnetic field simultaneously,which provides an important opportunity for the synergy of multiple external fields to achieve enhanced caloric effect.However,the caloric effect of phase change under the combining hydrostatic pressure and magnetic field is mainly measured by indirect method.This method exists some problems such as poor accuracy and inconsistent testing standards.In view of the problems above,we designed and built a barocaloric effect system based on the principle of DTA(Differential Thermal Analysis),and reported a giant barocaloric effect in PdNMn3 compound with small thermal hysteresis.In addition,based on the HP-DTA system,we also successfully built a HPM-DTA testing system.Using this system,we study the multiple-field induced caloric effect of Mn0.6Fe0.4NiGe0.5Si0.5 alloy.The results show that the caloric effect of this alloy is enhanced by the synergistic cooperation of multiple external fields.The main contents of this paper are as follows:1.We designed and built a HP-DTA and a HPM-DTA testing systems.The structure of the high-pressure mould,the hardware and software are self-designed.The maximum pressure can reach 1GPa due to the use of a hydraulic pressure supply system.Pressure calibration adopted digital pressure sensor combined with manganese-copper alloy pressure sensor,which can realize accurate application and real-time monitoring the pressure of sample.Using of heating wire and liquid nitrogen combined with the PID(Proportion Integral Differential)algorithm can achieve precise temperature control of a wide temperature range and high speed for the pressure mould.It was tested that the baseline noise is about 0.06 uV,the baseline drift is 4.1 uV and the error of temperature change rate is about 6.7%.Moreover,GaNMn3 was also tested in commercial HP-DSC(High Pressure Differential Scanning Calorimetry)as a standard sample.The HP-DSC data also can verifiy the accuracy of the self-built DTA.In addition,based on the PPMS(Physical Property Measurement System)platform,a HPM-DTA testing systems was successfully built.It was measured that the baseline noise is about 0.18 uV,the baseline drift is 6.6 uV and the error of temperature change rate is about 6-10%.The Mn0.6Fe0.4NiSi0.5Ge0.5 alloy was used for systematic verification which also proves the stability and reliability of this device.2.We report the giant BC effect along with weak hysteresis at the antiferromagnetic(AFM)to paramagnetic(PM)phase transition(TN=283 K)in antiperovskite PdNMn3 compound.The reversible isothermal entropy change reaches 28.3 J/kg K under 290 MPa.The hysteresis is only about 2 K,which is associated with a small volumetric change ΔV/V at TN(～0.2%).The magnetic entropy is proposed to mainly contribute to the entropy change at TN,which compensates for the reduced lattice contribution due to the small ΔV/V.Our result demonstrates the possibility of realizing giant BC effect together with weak hysteresis in materials where both crystallographic and non-crystallographic entropy changes cooperate at the first-order phase transition(FOPT).3.We proposed a quasi-direct method for caloric effect measurements under the combination of magnetic field and hydrostatic pressure.By combining two external fields in a proper sequence,the reversible caloric effect of Mn0.6Fe0.4NiSi0.5Ge0.5 alloy was markedly enhanced.Our method can be expanded to study the multiple-field induced caloric effect in other multiferroic materials and promote the development of solid-state refrigeration in practical applications.The establishment of HP-DTA and HPM-DTA testing systems makes up for the blank of domestic self-made barocaloric and multi-caloric(magnetic field and hydrostatic pressure)testing systems.It is very useful for the development of barocaloric or multi-caloric demos and the other industrial products.On this basis,the large reversible barocaloric effect of PdNMn3 compound was studied,and it was found that the large barocaloric effect of the PdNMn3 compound came from the spin-entropy compensation mechanism in the system.In addition,the multi-field driven phase transition caloric effect of Mn0.6Fe0.4NiSi0.5Ge0.5 alloy was studied,and it was found that the synergistic effect of the two external fields can greatly improve the reversible phase transition caloric effect of the alloy.It also provides a new idea for the study of multi-field composite solid-state refrigeration technology.