Effects Of Sintering Temperature And Graphene Substitution On The Properties And Structures Of MnFePGe Compounds

In recent years,humans have developed some refrigeration techniques to resolve the serious challenges of environment and energy.Magnetic refrigeration is the most promising technique due to the potential atmosphere friendly,energy saving.As an important part of magnetic refrigeration,excellent magnetic refrigeration materials are rather vital for achieving the maximum work efficiency.Compared with other magnetic refrigeration materials,MnFePGe compound is one of the outstanding candidates due to giant magnetocaloric effect?MCE?,non-toxic and lower cost.In this paper,nominal Mn_1.2Fe_0.8P_0.73Ge_0.27 compounds,including a diameter38mm sample making sure the consistency of initial components,sintering at different temperatures were prepared via mechanical milling?MA?and subsequent spark plasma sintering?SPS?technique.And their crystal structures,micromorphology,phase transition process and properties were investigated by XRD,SEM,DSC.The results show that these compounds possess a hexagonal Fe₂P-type crystal structure,and higher sintering temperature can promote the transformation of impurity phase Ge₆Fe₃Mn₄ to main phase Mn_1.2Fe_0.8P_0.73Ge_0.27.The average grain size and maximum grain size increases with higher sintering temperature.Also,Higher sintering temperature can enhance the entropy change,improve the Curie temperature T_c,and narrow the two-phase coexistence range(?T_coex).Hence,we can improve the properties of the compounds by increasing sintering temperature.In addition,Mn_1.2Fe_0.8P_0.73Ge_0.27C_x?x=0,0.001,0.003,0.005,0.021?compounds were prepared by the above way.We found that the addition of graphene degenerates the magnetocaloric properties slightly by virtue of smaller grain size and the percentage of Mn_1.2Fe_0.8P_0.73Ge_0.27 phase.However,a very few additives can keep the rather magnetocaloric properties,and improve the thermal conductivity of Mn_1.2Fe_0.8P_0.73Ge_0.27C_x?x=0.001,0.003?as much as 7.39 and 9.78 W·m^-1·K^-1,which is1.07 and 1.42 times than Mn_1.2Fe_0.8P_0.73Ge_0.27,respectively.Therefore,we propose to enhance the thermal conductivity,and keep their magnetocaloric properties by adding graphene.In conclusion,the results indicate that MnFePGe compound can be a very promising material for magnetic refrigeration around room temperature.We can improve the magnetocaloric properties of this compound by higher sintering temperature,enhance the thermal conductivity via adding graphene as well to meet application requirements in fact.