成分配比及Se替代对MnFePGe化合物磁热性能和结构的影响
发布时间：2018-10-18 12:00
【摘要】：利用机械合金化(MA)结合放电等离子烧结(SPS)技术，制备了Mn1.2Fe0.8P1-yGey(y=0.25,0.26,0.27)、MnxFe2-xP0.74Ge0.26(x=1.13,1.15,1.18,1.20,1.22)和Mn1.2Fe0.8P0.74Ge0.26-zSez(z=0,0.005,0.01,0.015,0.02,0.03)化合物，采用X射线衍射(XRD)、差热扫描量热仪(DSC)、振动样品磁强计(VSM)和磁热效应直接测量仪对其晶体结构、相变过程及磁热性能进行了研究，并探讨了其间的相互关联。同时研究了均匀化退火对化合物磁热性能和微观结构的影响。得到以下研究成果： (1)采用MA和SPS技术制备的Mn1.2Fe0.8P1-yGey、 MnxFe2-xP0.74Ge0.26和Mn1.2Fe0.8P0.74Ge0.26-zSez化合物均为六方Fe2P结构，空间群P62m，杂相非常少。 (2)随着Mn含量的增加，化合物的Curie温度TC、热滞Thys、转变温区Tcoex、熵变SDSC和磁熵变SM都逐渐降低或减小，而化合物的绝热温变Tad在Mn含量较少(x=1.13)或者较多(x=1.22)时达到最大；随着Ge含量的增加，化合物的TC逐渐升高， Thys逐渐减小， SDSC和SM先增大后减小，而Tcoex逐渐宽化， Tad大幅度降低；少量Se (z≤0.015)对Ge的置换能够使化合物的TC升高， Tcoex变窄， Tad增大，而Thys和SDSC基本不变。因此，通过调节化合物中的Mn/Fe和P/Ge比以及采用少量Se替代Ge都可以有效改善化合物的磁热性能。 (3)均匀化退火减轻了Mn1.2Fe0.8P0.74Ge0.26化合物中的元素偏聚，使主相成分微调且晶粒长大，从而引起了化合物的SDSC、 SM和Tad增大，， Tcoex变窄，而TC和Thys基本保持不变。因此，合理的均匀化退火处理可以有效改善化合物的磁热性能。 (4)相对于其它组分，Mn1.18Fe0.82P0.74Ge0.26和Mn1.2Fe0.8P0.74Ge0.25Se0.01化合物的磁热性能较为优异，是很有应用前景的室温磁制冷材料。前者的TC、 Tcoex、 Thys和Tad分别为293.8，7.3，3.1和2.1K， SDSC和SM分别为26.0和19.0J/(kg·K)；后者的TC、 Tcoex、 Thys和Tad分别为285.8，7.6，3.2和2.2K， SDSC和SM分别为24.4和18.6J/(kg·K)。 (5)随着Ge含量的增加，化合物的晶格常数a和体积V逐渐增大，c和c/a逐渐减小；随着Se含量的增加，化合物晶格常数a和体积V发生了明显的变化，c与c/a先减小后增大；随着Mn含量的增加，化合物的晶格常数a和c发生了明显变化，晶胞体积V逐渐增大，c/a没有规律。分析表明Ge和Se会优先占据六方Fe2P结构中的2c位置，并通过减小c/a提高化合物Curie温度。而Mn会优先占据六方Fe2P结构中的3g位置，Mn含量增加会减弱化合物的一级相变特征。 (6)总之，可以通过同时调节Mn、Ge和Se这3种元素的含量来获得综合性能符合应用要求的室温磁制冷材料，即Curie温度在室温附近，滞后很小，两相共存区较窄，熵变和绝热温变较大。
[Abstract]:By means of mechanical alloying (MA) and spark plasma sintered (SPS) technique, the crystal structures of Mn1.2Fe0.8P1-yGey, MnxFe2-xP0.74Ge0.26 and Mn1.2Fe0.8P0.74Ge0.26-zSez were prepared by means of (DSC), vibrating sample magnetometer (VSM) and direct magnetocalorimeter (VSM) with X-ray diffraction (XRD), differential scanning calorimeter (DSC),) and direct magnetocalorimeter (VSM). The phase transition process and magnetocaloric properties are studied and the correlation between them is discussed. At the same time, the effect of homogenization annealing on the magnetocalorimetric properties and microstructure of the compounds was studied. The main results are as follows: (1) the Mn1.2Fe0.8P1-yGey, MnxFe2-xP0.74Ge0.26 and Mn1.2Fe0.8P0.74Ge0.26-zSez compounds prepared by MA and SPS have hexagonal Fe2P structure, space group P62 m, and very few heterophases. (2) with the increase of Mn content, The Tcoex, entropy and magnetic entropy of the compound decreased or decreased gradually in the TC, thermal lag Thys, transition temperature range, while the adiabatic Tad reached the maximum when the Mn content was less (XN 1.13) or more (XN 1.22), and with the increase of Ge content, the Tcoex, entropy and the magnetic entropy of the compound decreased or decreased gradually, while the adiabatic temperature variation of the compound reached the maximum when the Mn content was less (XN 1.13) or more (XN 1.22). The TC of the compound increased gradually, the Thys decreased, the SDSC and SM increased first and then decreased, while the Tcoex became wider and the Tad decreased significantly, and a small amount of Se (z 鈮
本文编号：2279061
[Abstract]:By means of mechanical alloying (MA) and spark plasma sintered (SPS) technique, the crystal structures of Mn1.2Fe0.8P1-yGey, MnxFe2-xP0.74Ge0.26 and Mn1.2Fe0.8P0.74Ge0.26-zSez were prepared by means of (DSC), vibrating sample magnetometer (VSM) and direct magnetocalorimeter (VSM) with X-ray diffraction (XRD), differential scanning calorimeter (DSC),) and direct magnetocalorimeter (VSM). The phase transition process and magnetocaloric properties are studied and the correlation between them is discussed. At the same time, the effect of homogenization annealing on the magnetocalorimetric properties and microstructure of the compounds was studied. The main results are as follows: (1) the Mn1.2Fe0.8P1-yGey, MnxFe2-xP0.74Ge0.26 and Mn1.2Fe0.8P0.74Ge0.26-zSez compounds prepared by MA and SPS have hexagonal Fe2P structure, space group P62 m, and very few heterophases. (2) with the increase of Mn content, The Tcoex, entropy and magnetic entropy of the compound decreased or decreased gradually in the TC, thermal lag Thys, transition temperature range, while the adiabatic Tad reached the maximum when the Mn content was less (XN 1.13) or more (XN 1.22), and with the increase of Ge content, the Tcoex, entropy and the magnetic entropy of the compound decreased or decreased gradually, while the adiabatic temperature variation of the compound reached the maximum when the Mn content was less (XN 1.13) or more (XN 1.22). The TC of the compound increased gradually, the Thys decreased, the SDSC and SM increased first and then decreased, while the Tcoex became wider and the Tad decreased significantly, and a small amount of Se (z 鈮
本文编号：2279061
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