【摘要】：利用機(jī)械合金化(MA)結(jié)合放電等離子燒結(jié)(SPS)技術(shù)，制備了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射線衍射(XRD)、差熱掃描量熱儀(DSC)、振動樣品磁強(qiáng)計(jì)(VSM)和磁熱效應(yīng)直接測量儀對其晶體結(jié)構(gòu)、相變過程及磁熱性能進(jìn)行了研究，并探討了其間的相互關(guān)聯(lián)。同時研究了均勻化退火對化合物磁熱性能和微觀結(jié)構(gòu)的影響。得到以下研究成果： (1)采用MA和SPS技術(shù)制備的Mn1.2Fe0.8P1-yGey、 MnxFe2-xP0.74Ge0.26和Mn1.2Fe0.8P0.74Ge0.26-zSez化合物均為六方Fe2P結(jié)構(gòu)，空間群P62m，雜相非常少。 (2)隨著Mn含量的增加，化合物的Curie溫度TC、熱滯Thys、轉(zhuǎn)變溫區(qū)Tcoex、熵變SDSC和磁熵變SM都逐漸降低或減小，而化合物的絕熱溫變Tad在Mn含量較少(x=1.13)或者較多(x=1.22)時達(dá)到最大；隨著Ge含量的增加，化合物的TC逐漸升高， Thys逐漸減小， SDSC和SM先增大后減小，而Tcoex逐漸寬化， Tad大幅度降低；少量Se (z≤0.015)對Ge的置換能夠使化合物的TC升高， Tcoex變窄， Tad增大，而Thys和SDSC基本不變。因此，通過調(diào)節(jié)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熱性能。 (3)均勻化退火減輕了Mn1.2Fe0.8P0.74Ge0.26化合物中的元素偏聚，使主相成分微調(diào)且晶粒長大，從而引起了化合物的SDSC、 SM和Tad增大，， Tcoex變窄，而TC和Thys基本保持不變。因此，合理的均勻化退火處理可以有效改善化合物的磁熱性能。 (4)相對于其它組分，Mn1.18Fe0.82P0.74Ge0.26和Mn1.2Fe0.8P0.74Ge0.25Se0.01化合物的磁熱性能較為優(yōu)異，是很有應(yīng)用前景的室溫磁制冷材料。前者的TC、 Tcoex、 Thys和Tad分別為293.8，7.3，3.1和2.1K， SDSC和SM分別為26.0和19.0J/(kg·K)；后者的TC、 Tcoex、 Thys和Tad分別為285.8，7.6，3.2和2.2K， SDSC和SM分別為24.4和18.6J/(kg·K)。 (5)隨著Ge含量的增加，化合物的晶格常數(shù)a和體積V逐漸增大，c和c/a逐漸減��；隨著Se含量的增加，化合物晶格常數(shù)a和體積V發(fā)生了明顯的變化，c與c/a先減小后增大；隨著Mn含量的增加，化合物的晶格常數(shù)a和c發(fā)生了明顯變化，晶胞體積V逐漸增大，c/a沒有規(guī)律。分析表明Ge和Se會優(yōu)先占據(jù)六方Fe2P結(jié)構(gòu)中的2c位置，并通過減小c/a提高化合物Curie溫度。而Mn會優(yōu)先占據(jù)六方Fe2P結(jié)構(gòu)中的3g位置，Mn含量增加會減弱化合物的一級相變特征。 (6)總之，可以通過同時調(diào)節(jié)Mn、Ge和Se這3種元素的含量來獲得綜合性能符合應(yīng)用要求的室溫磁制冷材料，即Curie溫度在室溫附近，滯后很小，兩相共存區(qū)較窄，熵變和絕熱溫變較大。
[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

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