因氟氯碳化物流體冷媒之逸散對溫室效應的加劇，使之將在2042年退出製冷市場，因此需要新型態的冷媒進行替代，而MnNiSi-based材料在致冷上被認為是能替代現今冷媒的材料能夠進行應用。在本篇研究中， MnNiSi 合金作為替代之磁冷媒材料，本實驗藉由置換MnFeGe合金，探討其相轉變溫度是否隨晶格扭曲而降低，並期望能使結構相轉變在室溫發生。
在此篇研究中，利用真空感應熔煉爐製備 MnNiSi與MnFeGe合金，藉由MnFeGe等結構合金之置換製成MnNiSi-Based合金，利用場發射掃描式電子顯微鏡(FE-SEM)、X 光繞射儀(XRD)及示差掃描熱卡量計(DSC)分析，探討微結構、晶體結構、結構相變化溫度之影響。MnNiSi 鐵磁性形狀記憶合金在 1197K 發生結構相變化，由 Orthorhombic 結構之低溫相轉變 Hexagonal 結構之高溫相。 (MnNiSi)1-x(MnFeGe)x合金樣品中，以Fe,Ge 置換部分 Ni, Si， 使合金原子有效置換 MnNiSi 合金原子之位置，晶體結構仍維持 Orthorhombic 結構；然而Fe, Ge因原子半徑及與 Ni, Si 形成鍵結長度相比較為大，使 Orthorhombic 結構之晶格產生扭曲，能量上升使結構傾向不穩定，進而降低 MnNiSi 之結構相轉變溫度。隨MnFeGe添加，結構轉變溫度隨晶格扭曲程度改變，在x=0.50時使 Orthorhombic 結構之晶格扭曲程度最大，晶格常數比值a/b由1.639降至1.580，相變化溫度由1197K降至371 K。然而，若更進一步置換MnFeGe雖成功將其高溫相拉低於室溫穩定成相，但並未發現其在室溫下的相轉變行為，不利於室溫磁致冷的應用。在此條件下，認為(MnNiSi)0.50(MnFeGe)0.50在本研究中為MnNiSi-based材料中具潛力之磁致冷材料。

Due to the aggravation of the greenhouse effect due to the leakage of CFC fluid refrigerants, it will be withdrawn from the refrigeration market in 2042, so new types of refrigerants are required to be replaced, and MnNiSi-based materials are considered to be able to replace in refrigeration. In this study, MnNiSi alloy is used as an alternative magnetic refrigerant material. By replacing MnFeGe alloy, this experiment investigates whether the phase transition temperature decreases with lattice distortion, and it is expected that the structural phase transition can occur at room temperature.
In this study, MnNiSi and MnFeGe alloys were prepared using a vacuum induction melting furnace, and MnNiSi-Based alloys were prepared by replacing isostructural alloys such as MnFeGe. Field emission Scanning Electron Microscopy (FE-SEM), X-ray diffraction (XRD) and Differential Scanning Calorimeter (DSC) analysis to explore the influence of microstructure, crystal structure, and structural phase change temperature. The MnNiSi ferromagnetic shape memory alloy undergoes a structural phase change at 1197K, from the low-temperature phase of the Orthorhombic structure to the high-temperature phase of the Hexagonal structure. In (MnNiSi)1-x(MnFeGe)x alloy samples, some Ni and Si are replaced by Fe and Ge, so that the alloy atoms can effectively replace the positions of MnNiSi alloy atoms, and the crystal structure still maintains the Orthorhombic structure. However, due to the atomic radius and Compared with Ni and Si, the bond length is relatively large, which makes the crystal lattice of Orthorhombic structure distorted, and the energy rise makes the structure tend to be unstable, thereby reducing the structural phase transition temperature of MnNiSi. With the addition of MnFeGe, the structural transition temperature changes with the degree of lattice distortion. When x=0.50, the degree of lattice distortion of the Orthorhombic structure is the largest, the lattice constant ratio a/b decreases from 1.639 to 1.580, and the phase change temperature decreases from 1197K to 371K. However, if MnFeGe is further replaced, although its high-temperature phase is successfully pulled down to a stable phase below room temperature, its phase transition behavior at room temperature has not been found, which is not conducive to the application of room temperature magnetic refrigeration. Under this condition, it is considered that (MnNiSi)0.50(MnFeGe)0.50 is a potential magnetic refrigeration material among MnNiSi-based materials in this study.

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