摘要

過渡金屬碳化物，M2AlC (M= Ti, V, Cr) 具有耐高溫高壓，高導電度與高熱導率，並且具有高度的抗氧化力與容易加工的特性，因此極具應用價值。
本篇論文提供以核磁共振(NMR)的技術研究這一系列三元素碳化物的電子結構與相關特性。在Ti2AlC， V2AlC及Cr2AlC材料的27Al NMR頻譜中，四重極效應與非均向的奈特位移所造成的效應皆經過理論計算而明確的標定。
均向的奈特位移在三者之間的變化趨勢顯示出過渡元素中的d電子與鋁的p電子之間所形成超精細作用隨著d電子數增加而增強。除此之外，我們對Cr2AlC做了自旋晶格鬆弛時間的變溫量測，從77K~ 300K的實驗結果符合順磁性金屬的趨勢。同時在自旋晶格鬆弛時間的量測上，顯示出Ti2AlC與V2AlC中鋁的s電子在費米能階處所貢獻的態密度與d電子增加有密切的關連性。

Abstract

Transit-metal carbides M2AlC (M= Ti, V, Cr) have many technological applications for their high elastic modulus, damage tolerance, excellent thermal and electrical conductivity.
In this letter we investigated the electronic structure and properties of the series ternary carbides M2AlC by nuclear magnetic resonance (NMR) techniques. In 27Al NMR spectrum of these materials, anisotropic Knight shift and quadrupole effects have been identified.
The isotropic Knight shift varies from positive for Ti2AlC and V2AlC to negative for Cr2AlC, corresponding to the transfer hyperfine field of the Al-M bond increasing with the d electron count. The quadrupole frequency points to the important Al-M bonding nature. T1 measurements provide the Al-s Fermi level DOS for Ti2AlC and V2AlC correlate with the transition d electron count. In addition, the temperature dependent T1 between 300K and 77K indicated the paramagnetic feature in Cr2AlC.

引用文獻

[1] Yanchun Zhou and Zhimei Sun, Phys. Rev. B 61, 12570 (2000)
[2] Zhimei Sun, Rajeev Ahuja, and Jochen M. Schneider, Phys. Rev. B
68,224112 (2003)
[3] Zhimei Sun, Rajeev Ahuja, Sa Li, and Jochen M. Schneider,
Appl. Phys. Lett. 83, 899 (2003)
[4] J. D. Hettinger, S. E. Lofland, P. Finkel, T. El-Raghy, and M. W. Barsoum, Phys. Rev. B 72, 115120 (2005)
[5] Zhimei Sun, Denis Music, Rajeev Ahuja, Sa Li, and Jochen M. Schneider,
Phys. Rev. B 70, 092102 (2004)
[6] C. S. Lue, A Nuclear magnetic resonance probe of Fe-V-Al intermetallics
(1999)
[7] C. S. Lue and Joseph H. Ross, Jr., Phys. Rev. B 58, 9763 (1998)
[8] C. S. Lue, J. Y. Lin, and B. X. Xie, Phys. Rev. B 73, 035125 (2006)
[9] C. P. Slichter, Principles of Magnetic Resonance (Springer Series in Solid State Sciences 1) (1996)
[10] C. S. Lue, B. X. Xie, S. N. Horng, J. H. Su, and J. Y. Lin, Phys. Rev. B 71, 195104 (2005)
[11] W. H. Jones, Jr., T. P. Graham, and R. G. Barnes, Phys. Rev. 132, 1898
(1963)
[12] M. H. Cohen and F. Reif, Solid State Physics (Academic Press, New
York, 1957) Vol.5, p.11.

[13] 核磁共振量測物質的微觀電磁性質，呂欽山, 賴文振編，物理雙月
刊(26卷3期) (2004)
[14] F. Y. Fradin and G. Cinader, Phys. Rev. B 16, 73 (1977)
[15] John J. Spokas and Charles P. Slichter, Phys. Rev. 113, 1462 (1959)
[16] C. S. Lue, Suchitra Chepin, James Chepin, and Joseph H. Ross, Jr., Phys. Rev. B 57, 7010 (1998)
[17] Jochen M. Schneider, Zhimei Sun, Raphael Mertens, Fatih Uestel, and
Rajeev Ahuja, Solid State Commun. 130 (2004) 445.
[18] 鋁摻雜對Heusler-type Fe2VSi 合金之結構及熱電性質影響, 洪聖楠,
成功大學物理所碩士論文 (2005)
[19] Charles Kittel, Introduction to Solid State Physics, 8th ed. 2005
[20] 許樹恩,吳泰伯，X光繞射原理與材料結構分析,中國材料科學學會
(1996)
[21] W. Jeitschko et al. MONATSHEFTE FUER CHEMIE 1963 94 p672
[22] 核磁共振研究過渡金屬元素二硼化合物, 賴文振, 成功大學物理所
碩士論文 (2004)
[23] International Centre for Diffraction Data.
[24] H.B. Zhuang, Y.C. Zhou, Y.W. Bao, M.S. Li, and J.Y. Wang, J.Eur.
Ceram. Soc. (2005)