Synthesis Of Plate-shaped La（Fe,Si）₁₃ Hydrides Under High-pressure Atmosphere And Study Of Magnetocaloric Effect

La（Fe,Si）₁₃ hydride is regarded as one of the most promising room-temperature magnetic refrigerants.Thin plate shape is an ideal structural feature for a typical active magnetic refrigerator（AMR）machine.However,a complete plate-shaped refrigerant can not be obtained by directly hydrogenation of a bulk due to the appearances of microcracks.In this paper,La_0.5Pr_0.5Fe_11.4Si_1.6,La_0.6Pr_0.4Fe_11.4Si_1.6B_0.2 and La_0.9Ce_0.1Fe_11.7-xMn_xSi_1.3 alloy ingots were made by arc-melting method.And then plate-shaped La（Fe,Si）₁₃ hydrides were synthesized by sintering in a self-made furnace in a high-purity H₂ gas atmosphere of 40 MPa or 50 MPa.Crystal and phase structures were analyzed by means of X-ray diffraction（XRD）.Microstructures of the samples were characterized by using a scanning electron microscopy（SEM）.Magnetic properties were measured in a superconducting quantum interference device（SQUID）magnetometer.Main studies of the paper were focused on the effect of duration or temperature of sintering,H₂-pressures and doping on crystal structures,phase components and magnetic properties of hydrides.Based on the reduction of hysteresis,AMR machine-suitable refrigerants with high magnetic refrigeration performance were synthesized.High density plate-shaped La_0.5Pr_0.5Fe_11.4Si_1.6 hydrides were prepared by sintering in a high-purity H₂ of 50 MPa and 600℃.High-pressure atmosphere suppresses the desorption of hydrogen atoms during the sintering process.And the phase structures and magnetocaloric effect of the hydrides were investigated.The sintered thin refrigerant exhibits a high magnetic-refrigeration performance with a maximal ΔS_m at 330 K of 15.5J/kg·K for the field change of 0-2T.Plate-shaped La_0.6Pr_0.4Fe_11.4Si_1.6B0.2 hydrides were prepared by sintering in a high-purity H₂ of 50 MPa and 600℃.And effect of B-doping on the phase structure and magnetocaloric effect was investigated by means of XRD and measurements of magnetic properties.The experimental results show that B-doping is able to improve the stability of 1:13 phase during the sintering process,and increases the Curie temperature of sintered sample while the hysteresis can be remarkably decreased.The sintered thin refrigerant exhibits a high magnetic-refrigeration performance with a maximal ΔS_m at 345 K of 16.2J/kg·K for the field change of 0-5T.A series of plate-shaped La_0.9Ce_0.1Fe_11.7-xMn_xSi_1.3（x=0,0.29,0.35,0.41）hydrides were prepared by sintering in a high-pressure H₂ atmosphere of 40 MPa and 700℃（or 500℃）.And effect of Mn-doping on the phase structure and magnetocaloric effect was investigated.Meanwhile,Mn-doping is beneficial for restraining the precipitation of α-Fe,and reduces the Curie temperature to around room temperature.A La_0.9Ce_0.1Fe_11.35Mn_0.35Si_1.3 thin plate-shaped hydride（prepared in 700℃）shows a magnetic-entropy change ΔS_m of 4.3 J/kg·K for a field change of 0-2T at 289 K.And the maximal ΔS_m at 290 K for a thin plate-shaped hydride（prepared in 500℃）for the field change of 0-2T（or 0-5T）is 7.5J/kg·K（or 12.4J/kg·K）.And the maximal temperature change ΔT_ad for the field change of 1.5T is as large as 2K.