本研究在探討多元合金是否也具有超導電性，藉此進一步了解高熵合金的物理性質。選擇實驗室已配製過的含Nb多元合金，進行電性量測，有MoNbTaW, MoNbTaVW及NbSiTaTiZr三種，並觀察到在低溫時，NbSiTaTiZr疑似有超導現象；因此對此合金進行成分改變，有NbTaTiZr, HfNbTaTiZr, NbGeTaTiZr, NbSiTaTiZrV, NbGeTaTiZrV, NbSiTaTiZrGe及NbSiTaTiZrGeV等七種，對以上共十種四至七元合金進行電性質、磁性質、霍爾效應等研究。以真空電弧熔煉，製備各種合金；試片經切割及研磨後，進行SEM、EDS、XRD、低溫到室溫(5 K ~ 300 K)電阻的四點量測、磁化量對溫度(2 K ~ 300 K)、磁滯曲線(5 K及300 K)、及「變溫與變磁場之霍爾效應」等量測與分析。
鑄造態MoNbTaW、NbTaTiZr、MoNbTaVW及HfNbTaTiZr的微結構，都是單一的、簡單固溶的「擬一元BCC結構」，且皆分成樹枝相及樹枝間相。其餘六種鑄造態合金內，都含有多結構的多相；但重要的是，含有擬一元BCC結構「富Nb-Ta固溶相」的合金，均具有超導電性。
有零電阻現象的合金及其臨界溫度，分別是NbTaTiZr (8.98 K), HfNbTaTiZr (7.93 K), NbGeTaTiZr (9.16 K), NbSiTaTiZrV (4.99 K), NbGeTaTiZrV (9.10 K)及NbSiTaTiZrGe (8.10 K)；而NbSiTaTiZr在低到約5 K時，電阻開始急遽降下，但因儀器限制，溫度無法再降低，故疑似在低於5 K時，有零電阻現象。
單一BCC結構的MoNbTaW與MoNbTaVW合金，係由BCC結構元素組成的，兩者的電阻率(約22 ~40 μΩ-cm)，較以往量測過的高熵合金電阻率(約100 ~200 μΩ-cm)為小。而七元NbSiTaTiZrGeV合金正常態電阻率(約200 μΩ-cm)是本研究合金正常態中最大的。而所有合金之殘餘電阻比值(RRR =ρ290/ρ10)在1.05 ~ 1.36之間，表示ρ10非溫度項影響因素，大於ρ290溫度項影響因素，符合高熵合金內擁有大量缺陷存在之過往結論。
從外加磁場為1 kOe下的M(T)曲線觀察，在以上電性量測中，具有及疑有超導電性的合金，都出現反磁現象；合金及臨界溫度為NbTaTiZr (7.98 K), HfNbTaTiZr (6.30 K), NbSiTaTiZr (4.92 K), NbSiTaTiZrV (4.73 K), NbGeTaTiZr (8.61 K), NbGeTaTiZrV (6.34 K), NbSiTaTiZrGe (5.94 K)，由此可驗證超導電性存在的現象；而在電性量測中，不發生超導電性的合金，皆看不出反(抗)磁的M(T)曲線。
對5 K下M(H)磁滯曲線進行分析，具有超導電性的合金，磁滯曲線均形成四個象限分布對稱的形狀，顯示為第二類超導體。藉磁滯曲線，可觀察到各合金的臨界磁場值。以Hc1來看，NbTaTiZr (400 Oe), NbSiTaTiZr (400 Oe), NbGeTaTiZr (300 Oe), NbGeTaTiZrV (300 Oe), NbSiTaTiZrGe (100 Oe)及HfNbTaTiZr (< 100 Oe)；而Hc2幾乎都超過1 T (因本實驗中，最大只能量測到1 T)，只有NbSiTaTiZrGe (6 kOe)較小。在300 K下，所有合金的磁滯曲線，都呈超順磁性或軟鐵磁性。
本研究合金5 K與300 K霍爾效應的量測顯示，載子多為「類電洞」，濃度約1022 cm-3，與過往之多元合金結果相似。各合金之載子遷移率在正常態下，比一般純金屬低一至二個數量級，變溫度的霍爾效應量測分析則顯示，隨著溫度漸高，霍爾電阻率也跟著升高。綜合霍爾效應之量測結果，也說明高熵合金的擬一元晶格中，確有大量的缺陷存在。
硬度最小的是NbTaTiZr合金(322 Hv)，加入Hf、Si、Ge等元素後，都使合金硬度上升；加入V後，合金硬度下降；而NbSiTaTiZrGeV合金具有最大的硬度(760 Hv)，推測係其內之相數最多，固溶強化效應顯著所致。

This study aims to explore if the high-entropy alloys (HEAs) also possess superconducting behaviors as conventional metals and alloys possess. By doing this, one may be able to understand further the properties of HEAs. Before systematic investigation, we first selected some known Nb-containing alloy and HEAs, such as MoNbTaW, MoNbTaVW, and NbSiTaTiZr, to check the R(T) behavior down to 5 K; and found the superconducting-like behavior of NbSiTaTiZr near that temperature. Therefore, we continued to design and to prepare NbTaTiZr, HfNbTaTiZr, NbGeTaTiZr, NbSiTaTiZrV, NbGeTatiZrV, NbSiTaTiZrGe, and NbSiTaTiZrGeV alloys; and performed the electrical and magnetic properties, and Hall measurements of these ten 4- to 7-component alloys. Alloy samples were vacuum-arc-remelted, cut, and ground, and then they were performed SEM, EDS, XRD, and 5-300 K 4-probe resistivity (T), 2-300 K magnetization M(T), and 5 K- and 300 K-hysteresis M(H) measurements, as well as varied-temperature and -magnetic field Hall measurement and analysis.
Microstructure of as-cast MoNbTaW, NbTaTiZr, MoNbTaVW, and HfNbTaTiZr are of single, simple, solid-solution, pseudo-unitary BCC with dendrite-interdendrite substructure. Other 6 as-cast alloys contain a structure with multi-structure and multi-phase in them. Of the most important is that all structures that contain Nb-Ta-riched, pseudo-unitary BCC, solid-solution phase possess superconductivity.
Alloys with zero electrical resistance and their corresponding critical temperatures are NbTaTiZr (8.98 K), GeNbTaTiZr (9.16 K), HfNbTaTiZr (7.93 K), NbSiTaTiVZr (4.99 K), GeNbSiTaTiZr (8.10 K), and GeNbTaTiVZr (9.10 K). As to NbSiTaTiZr, it has a drastic drop in resistance near 5 K. Owing to the limitation of measurement that experimental temperature cannot be lowered further; it therefore shows zero-like resistance in the electrical resistance measurements.
Single BCC-structured MoNbTaW and MoNbTaVW alloys are composed of all BCC elements, their electrical resistivity ranges 22~40 μΩ-cm, which is lower than that (100~200 μΩ-cm) of other non-all-BCC multi-component alloys measured as before. The 7-component NbSiTaTiZrGeV alloy has the highest resistivity of ~200 μΩ-cm among the ten alloys in this study. The value of residual resistivity ratio, RRR  290K/10K, is in 1.05 ~ 1.36, manifesting that the non-thermal effect, i.e., lattice defect, is greater than the thermal factor. The latter conclusion is in consistent with the one ever made in the similar experiments.
From M(T) curves at 1 kOe, alloys that have superconductivity or the like in resistivity measurements show definite diamagnetism. These alloys with their corresponding critical temperatures are NbTaTiZr (7.98 K), NbSiTaTiZr (4.92 K), NbSiTaTiVZr (4.73 K), GeNbTaTiZr (8.61 K), GeNbTaTiVZr (6.34 K), GeNbSiTaTiZr (5.94 K), and HfNbTaTiZr (6.30 K). These M(T) experiments demonstrate the existence of superconductivity in these alloys. On the other hand, the alloys without zero resistivity show no diamagnetic behavior in M(T).
Measurements of M(H) hysteresis at 5 K with superconducting alloys show a loop extended in 4 quadrants, demonstrating that these alloys are of the type II superconductors. By M(H), one is able to determine the critical magnetic fields of superconducting alloys. The lower critical magnetic field, Hc1, in alloys and their corresponding values are NbTaTiZr (400 Oe), NbSiTaTiZr (400 Oe), GeNbTaTiZr (300 Oe), GeNbTaTiVZr (300 Oe), GeNbSiTaTiZr (100 Oe), and HfNbTaTiZr (< 100 Oe). The higher critical magnetic field, Hc2, in almost alloys is exceeding 1 T (104 G). Only GeNbSiTaTiZr show small Hc2 (6 kOe). M(H) measurements at 300 K for all ten alloys show superparamagnetism or soft ferromagnetism.
Hall measurements at 5 and 300 K and at 1 T to 9 T for these multi-component alloys demonstrate that most of the carriers are of hole-like, with concentration of 1022 cm-3 that is the same value measured as before. The mobility of the alloys is one or two orders of magnitude less than that of the pure metals. As temperature rises, the Hall resistivity increases. The summary in Hall measurements elucidates that there is a large amount of point defects in the pseudo-unitary lattice of the multi-component alloys.
Alloy that has the lowest hardness (322 Hv) is NbTaTiZr. The hardness value increases after the individual addition of Hf, Si, and Ge in NbTaTiZr, while the V addition in it decreases the hardness of the alloy. The NbSiTaTiZrGeV alloy has the largest hardness value (760 Hv) that is ascribed to its largest number of multi-phases and a significant effect of the solid solution strengthening.

1. J.W. Yeh, S.K. Chen, S.J. Lin, J. Y. Gan, T. S. Tsau, and S.Y. Chang, Nano structured High-Entropy Alloys with Multiple Principal Elements:Novel Alloy Design Concepts and Outcomes, Advanced Engineering Materials, 6 (2004) 299-303.
2. 黃國雄, 等莫耳比多元合金系統之研究, 國立清華大學材料科學工程研究所碩士論文 (1996).
3. 賴高廷, 高亂度合金微結構及性質探討, 國立清華大學材料科學工程研究所碩士論文 (1998).
4. 許雲翔, 以FCC及BCC元素為劃分配置等莫耳等多元合金系統之研究, 國立清華大學材料科學工程研究所碩士論文 (2000).
5. 洪育德, Cu-Ni-Al-Co-Cr-Fe-Si-Ti高亂度合金之探討, 國立清華大學材料科學工程研究所碩士論文 (2001).
6. 童重縉, Cu-Co-Ni-Cr-Al-Fe高熵合金變形結構與高溫特性之研究, 國立清華大學材料科學工程研究所碩士論文 (2002).
7. A. Inoue, T. Zhang, and T. Masumoto, Zr-Al-Ni amorphous alloys with high glass transition temperature and significant supercooled liquid region, Materials Transactions, JIM 31 (1990) 177-183.
8. A. Inoue, T. Zhang, K. Ohba, and T. Shibata, Continuous-Cooling-Transformation (CCT) Curves for Zr-Al-Ni-Cu Supercooled Liquids to Amorphous or Crystalline Phase, Materials Transactions, JIM 36 (1995) 876-878.
9. W. Stevenson, Metals Handbook, 9th ed., p.773, (ASM, Ohio, 1985).
10. 謝承安, 微結構對高熵合金的電與磁性質之影響, 國立清華大學材料科學工程研究所碩士論文 (2005).
11. 陳廷傑, 簡單相高熵合金AlxCoCrFeNi(0 ≤ x ≤ 2)之電性質研究, 國立清華大學材料科學工程研究所碩士論文 (2006).
12. 林川翔, 從Al, Co, Cr, Fe, Ni, Ti選取五至六元高熵合金之電與磁性質研究, 國立清華大學材料科學工程研究所碩士論文 (2008).
13. 周萱苹, AlxCoCrFeNi (0 ≤ x ≤ 2)高熵合金之導熱、熱膨脹及導電研究, 國立清華大學材料科學工程研究所碩士論文 (2008).
14. 朱柏州, 多種五元及六元Al, Co, Cr, Fe, Ni與Ti高熵合金之霍爾效應及相關電與磁性質研究, 國立清華大學材料科學工程研究所碩士論文 (2009).
15. 許致遠, FCC單相與BCC-FCC雙相Al0.25CoCrFeNix(0.25 ≤ x ≤ 2)高熵合金之Hall效應、電性與磁性研究, 國立清華大學材料科學工程研究所碩士論文 (2010).
16. 丁健峰, 三元到九元傳統合金與高熵合金磁性、電性、與霍爾效應之研究, 國立清華大學材料科學工程研究所碩士論文 (2011).
17. 黃炳剛, 多元高熵合金於熱熔射塗層之研究, 國立清華大學材料科學工程研究所碩士論文 (2003).
18. 陳宣佑, Al-Cr-Fe-Mn-Ni高熵合金變形與退火行為之研究, 國立清華大學材料科學工程研究所碩士論文 (2004).
19. 郭彥甫, Al-Cr-Fe-Mn-Ni高熵合金變形及退火行為之研究, 國立清華大學材料科學工程研究所碩士論文 (2005).
20. 劉宗憲, 非等莫耳六元CoxFeMnyTiVZr(0 ≤ x, y ≤ 2)高熵合金之儲氫研究, 國立清華大學材料科學工程研究所碩士論文 (2010).
21. 鄭耿豪, 利用射頻磁控濺鍍法製備高熵合金氮化物硬質薄膜, 國立清華大學材料科學工程研究所碩士論文 (2005).
22. D. Wei, Solid State Physics, p. 100-131, (Qing hua da xue chu ban she, Beijing, 2003).
23. C. Kittel, Introduction to Solid State Physics, 8th ed., p.134-157, (Wiley, Hoboken, NJ, 2005).
24. W. Gao and N. M. Sammes, An Introduction to Electronic and Ionic Materials, p. 8-32 (World Scientific, Singapore, 1999).
25. H. Benson, University physics, revised ed., p. 536, (John Wiley, New York, 1996).
26. David Jiles, Introduction to Magnetism and Magnetic Materials, (Chapman and Hall, London, 1991).
27. 近角聰信, 張煦、李學養 譯, 磁性物理學, p. 8-13(聯經出版社, 台灣, 1982).
28. N. A. Spaldin, Magnetic Materials Fundamentals and Applications,
p. 49-52, (Cambridge University Press, London, 2010).
29. 郭彥廷, 顆粒間交互作用對奈米金自發磁性之影響, 國立中央大學物理研究所碩士論文 (2008).
30. Tinkham, Introduction to superconductivity, 2nd ed., (McGraw-Hill Book Co., New York, 2004).
31. C. P. Poole, H. A. Farach, R. J. Creswick, R. Prozorov, Superconductivity, 2nd Ed., (Academic Press, 1995).
32. Pierre-Gilles de Gennes, Superconductivity of metals and alloys, (Perseus Books, America, 1999).
33. Kostas Gavroglu and Yorgos Goudaroulis, Heike Kamerlingh Onnes' researches at Leiden and their methodological implications, Studies In History and Philosophy of Science Part A, 19 (1988) 243–274.
34. Donald M. Ginsberg, Physical Properties of High Temperature Superconductors ш, (World Scientific, Singapore, 1992).
35. Vitaly L. Ginzburg, The Nobel Prize in Physics 2003 lecture On Superconductivity and Superfluidity.
36. K. H. Bennemann, John Boyd Ketterson, The Physics of Superconductors: Superconductivity in Nanostructures, High-Tc and Novel Superconductors, Organic Super-conductors, (Springer, Germany, 2004).
37. Adir Moyses Luiz, Superconductor, p. 17-46, (Sciyo, rijeka, 2010).
38. 張嵩駿、劉如熹、佘瑞琳, 奇妙的超導世界, 台灣大學化學系.
39. D.C. Larbalestier, M. O. Rikel, L.D. Cooley, A.A. Polyanskii, J.Y. Jiang, S. Patnaik, X.Y. Cai, D.M. Feldmann, A. Gurevich, A.A. Squitieri, M.T. Naus, C. B. Eom, E.E. Hellstrom, R.J. Cava, K.A. Regan, N. Rogado, M.A. Hayward, T. He, J.S. Slusky, P. Khalifah, K. Inumaru, M. Haas, Strongly linked current flow in polycrystalline forms of the superconductor MgB2, Nature, 410 (2001) 186.
40. 吳添全、洪連輝, 倫敦方程和穿透深度(The London Theory and Penetration Depth), 國立虎尾科技大學電子工程系/國立彰化師範大學.
41. S.K. Pan, UC Berkeley (2002), presented on NCTS “vortex matter” summer school, Hsinchu.
42. 儒森斯坦, 2003年諾貝爾物理獎得主---阿布里卡索夫(A. A. Abrikosov), 物理雙月刊 26, p. 24 (2004).
43. 施仁斌, 超導的世界, 逢甲大學電子系.
44. E. H. Hall, On a new action of the magnet on electric currents, Am. J. Math, 2 (1879) 287-292.
45. C. M. Hurd, The Hall Effect in Metals and Alloys, p. 153-182 (Plenum Press, New York, 1972).
46. C. L. Chien and C. R. Westgate, The Hall Effect and Its Applications, p. 55-74, (Plenum Press, New York, 1980).
47. 楊鴻昌, 超導量子干涉磁量儀, 科儀新知 12, p.72-79 (1991).
48. David Larbalestier, Alex Gurevich, D. Matthew Feldmann, Anatoly Polyanskii, High-Tc superconducting materials for electric power applications, Nature, 414 (2001) 368.
49. E. M. Gyorgy, R. B. van Dover, K. A. Jackson, L. F. Schneemeyer, J. V. Waszczak, Anisotropic critical currents in Ba2YCu3O7 analyzed using an extended Bean model, Appl. Phys. Lett., 55 (1989) 283-286.
50. D. Dew-Hughes, The critical current of superconductors: an historical review, low temperature physics, 27 (2001) 967-979.
51. Abrikosov A. A., On the magnetic properties of superconductors of the second group, Sov. Phys., 5 (1957) 1174-1182.
52. W. B. Pearson, A Handbook of Lattice Spacings and Structures of Metals and Alloys, (Pergamon Press, New York, 1958).
53. A. Takeuchi and A. Inoue, Classification of bulk metallic glasses by atomic size difference, heat of mixing and period of constituent elements and its application to characterization of the main alloying elements, Materials Transactons,JIM 46 (2005) 2817-2829.