Li2CuO2晶格結構的主要基礎為一個共邊鏈的CuO2。鋰離子沿c軸方向與CuO2交錯堆疊成一正交晶系結構，其晶格常數為a = 3.66 Å，b = 2.86 Å，c = 8.94 Å，銅-氧-銅間的鍵角為93°。此系統具反鐵磁性質，其尼爾溫度約在 TN ~ 9 K，在2.6 K為鐵磁自旋傾斜。Cu2+離子在此系統中為自旋1/2，根據古典海森堡模型理論計算，其有效磁矩為 1.732 μB。然而在實驗上利用居里外斯定律分析磁化率，得到有效磁矩的結果大於1.732 μB，E. M. L. Chung等人從中子繞射實驗發現氧具有自旋，我們進而推論氧缺陷為主因。
　　為了驗證有效磁矩增加是否真為氧缺陷所造成，我們設計了在不同氧壓力和七大氣壓下調變氧分壓，藉以調整氧缺陷在單晶樣品中的含量。利用光學聚焦區浮爐成長單晶樣品，並使用x光粉末繞射能譜、感應耦合電漿質譜儀、熱重分析儀及超導量子干涉磁量儀、分析氧缺陷對樣品物性的影響。實驗結果顯示多餘的磁矩是由氧缺陷所提供。

Li2CuO2 has a crystal structure composed of edge-shared CuO2 chains. The lattices constants are a = 3.66 Å, b = 2.86 Å, c = 8.94 Å, and the bond angle of Cu-O-Cu is 93°. This material orders antiferromagnetically below TN ~ 9 K, and canted at 2.6 K. The Cu2+ spin is expected to be 1/2 with effective moment of 1.732 μB. However, the magnetic susceptibility data fitted with Curie-Weiss law always suggest that the effective moment is higher than 1.732 μB, the excess magnetic moment beyond 1.732 µB is likely provided by the oxygen defects, as suggested from the neutron scattering studies by E. M. L. Chung et al.
　　We have synthesized single crystals by using floating-zone method under various oxygen pressures and high pressure of various oxygen partial pressures. This is an effective way to tune the oxygen deficiency level. The effective moment dependence of oxygen defect levels is examined using x-ray powder diffraction (XRPD), inductively coupled plasma-mass spectrometry (ICP-MS), thermo gravimetric analyzer (TGA), and superconducting quantum interference device (SQUID). Our results indicate that excess effective magnetic moments in Li2CuO2 is indeed provided by oxygen defects.

[1] J. Orenstein and A. J. Millis, “Advances in the physics of high-temperature superconductivity”, Science 288, 468 (2000).
[2] J. Paglione and R. L. Greene, “High-temperature superconductivity in iron-based materials”, Nature Physics 6, 645 (2010).
[3] N. Read and S. Sachdev, “Spin-peierls, valence-bond solid, and Nèel ground states of low-dimensional quantum antiferromagnets”, Phys. Rev. B 42, 4568 (1990).
[4] Y. Tokura and N. Nagaosa, “Orbital physics in transition-metal oxides”, Science 288, 462 (2000).
[5] M. Imda, A. Fujimori, and T. Tokura, “Metal-insulator transitions”, Rev. Mod. Phys. 70, 1039 (1998).
[6] A. J. Millis, “Lattice effects in magnetoresistive manganese perovskites”, Nature 392, 147 (1998).
[7] Y. Tokura, “Colossal Magnetoresistive Oxides”, Gordon and Breach, London (2000).
[8] T. Learmonth, C. M. Guinness, P. A. Glans, J. E. Downes, T. Schmitt, L. C. Duda, J. H. Guo, F. C. Chou, and K. E. Smith, “Observation of multiple Zhang-Rice excitations in a correlated solid: Resonant inelastic x-ray scattering study of Li2CuO2”, Europhys. Lett. 79, 47012 (2007).
[9] Coen de Graaf, Ibe´rio de P. R. Moreira, Francesc Illas, O scar Iglesias, and Amı´lcar Labarta, “Magnetic structure of Li2CuO2: Fromab initio calculations to macroscopic simulations”, Int. J. Mol. Sci. 1, 28 (2000).
[10] V. Yushankhai, L. Siurakshina, and R. Hayn, “Ring exchange in transition metal oxides: a new manifestation in Li2CuO2 ? ”, Physica B 726, 312 (2002).
[11] R. Hoppe and H. Riek, “Die kristallstruktur von Li2CuO2”, Chem. 379, 157 (1970).
[12] F. Sapiña, J. Rodríguez-Carvajal, M. J. Sanchis, R. Ibáñez, A. Beltrán, and D. Beltrán, “Crystal and magnetic structure of Li2CuO2”, Solid State Commun. 74, 779 (1990).
[13] A. S. Prakash, D. Larcher, M. Morcrette, M. S. Hegde, J. B. Leriche, and C. Masquelier, “Synthesis, phase stability, and electrochemically driven transformations in the LiCuO2-Li2CuO2 system”, Chem. Mater. 17, 4406 (2005).
[14] S. Patat, D. P. Blunt, A. M. Chippindale, and P. G. Dickens, “The thermochemistry of LiCuO, Li2CuO2 and LiCu2O2”, Solid State Ionics 46, 325 (1991).
[15] W. E. A. Lorenz, R. O. Kuzian, S. L. Drechsler, W. D. Stein, N. Wizent, G. Behr, J. Malek, U. Nitzsche, H. Rosner, A. Hiess, W. Schmidt, R. Klingeler, M. Loewenhaupt, and B. Buchner, “Highly dispersive spin excitations in the chain cuprate Li2CuO2”, Europhys. Lett. 88, 37002 (2009).
[16] M. Boehm, S. Coad, B. Roessli, A. Zheludev, M. Zolliker, P. Böni, D. M. Paul, H. Eisaki, N. Motoyama, and S. Uchida, “Competing exchange interactions in Li2CuO2”, Europhys. Lett. 43, 77 (1998).
[17] H. J. Xiang, C. Lee, and M. H. Whangbo, “Absence of a spiral magnetic order in Li2CuO2 containing one-dimensional CuO2 ribbon chains”, Phys. Rev. B 76, 220411 (2007).
[18] E. M. L. Chung, G. J. McIntyre, D. McK. Paul, G. Balakrishnan, and M. R. Lees, “Oxygen moment formation and canting in Li2CuO2” Phys. Rev. B 68, 144410 (2003).
[19] R. Weht and W. E. Pickett, “Extended moment formation and second neighbor coupling in Li2CuO2”, Phys. Rev. Lett. 81, 2502 (1998).
[20] M. Matsuda, K. M. Kojima, Y. J. Uemura, J. L. Zarestky, K. Nakajima, K. Kakurai, T. Yokoo, S. M. Shapiro, and G. Shirane, “Ordering of oxygen moments in ferromagnetic edge-sharing CuO4 chains in La14-xCaxCu24O41”, Phys. Rev. B 57, 11467 (1998).
[21] U. Staub, B. Roessli, and A. Amato, “Magnetic ordering in Li2CuO2 studied by µSR technique”, Physica B 289, 299 (2000).
[22] R. J. Ortega, P. J. Jensen, K. V. Rao, F. Sapiña, D. Beltrań, Z. Iqbal, J. C. Cooley, and J. L. Smith, “A field induced ferromagnetic-like transition below 2.8 K in Li2CuO2: An experimental and theoretical study”, J. Appl. Phys. 83, 6542 (1998).
[23] Z. Li, J. S. Tse, S. You, C. Q. Jin, and T. Iitaka, “Electronicand magnetic structure of the high pressure phase of Li2CuO2”, Int. J. Mod Phys B 25, 3409 (2011).
[24] S. Youa, Z. Li, L. Yang, C. Dong, L. C. Chen, C. J. Hu, G. Shen, and H. Mao, “High pressure induced coordination evolution in chain compound Li2CuO2”, J. Solid State Chem. 182, 3085 (2009).
[25] R. Neudert, H. Rosner, S. L. Drechsler, M. Kielwein, M. Sing, Z. Hu, M. Knupfer, M. S. Golden, and J. Fink, “Unoccupied electronic structure of Li2CuO2”, Phys. Rev. B 60, 13413 (1999).
[26] Z. Hu, S. L. Drechsler, J. M. Alek, H. Rosner, R. Neudert, M. Knupfer, M. S. Golden, J. Fink, J. Karpinski, G. Kaindl, C. Hellwig, and Ch. Jung, “Doped holes in edge-shared CuO2 chains and the dynamic spectral weight transfer in X-ray absorption spectroscopy”, Europhys. Lett. 59, 135 (2002).
[27] Y. J. Kim, J. P. Hill, F. C. Chou, D. Casa, T. Gog, and C. T. Venkataraman, “Charge and orbital excitations in Li2CuO2” Phys. Rev. B 69, 155105 (2004).
[28] S. M. Koohpayeh, D. Fort, and J. S. Abell, “The optical floating zone technique: A review of experimental procedures with special reference to oxides”, Prog. Cryst. Growth Charact. Mater. 54, 121 (2008).
[29] S. M. Koohpayeh, D. Fort, A. Bradshaw, and J. S. Abell, “Thermal characterization of an optical floating zone furnace: A direct link with controllable growth parameters”, J. Cryst. Growth 311, 2513 (2009).
[30] W. Jaime, “Phase diagrams: a literature source book”, Elsevier publishing (1981).
[31] D8 Advance pre-installation Guide
[32] B. G. Streetman, “Solid state electronic devices”, 6th edition, Prentice Hall publishing (1972).
[33] B. D. Cullity, “Elements Of X-ray Diffraction”, 1st edition, Addison Wesley publishing (1965).
[34] N. W. Ashcroft and N. D. Mermin, “Solid State Physics”, Victoria publishing (1976).
[35] C. Kittel, “Introduction To Solid State Physics”, 8th edition, John Wiley and Sons publishing (2004).
[36] Guide to using Agilent 7500 Series ICP-MS.
[37] M. Karppinen, A. Fukuoka, L. Niinistö, and H. Yamauchi, “Determination of oxygen content and metal valences in oxide superconductors by chemical methods”, Supercond. Sci. Technol. 9, 121 (1996).
[38] Guide to using MPMS SQUID VSM.
[39] 邱緯航、葉名倉，國科會高瞻自然科學教學資源平台，2010年。
[40] M. T. Weller and D. R. Lines, “Structure and oxidation state relationships in ternary copper oxides’’, J. Solid State Chem. 82, 21 (1989).
[41] B. J. Volicer and S. F. Tello, “The structure of simple solids”, chapter 3, Umass Lowell publishing (1998).
[42] S. Immel, Technical University of Darmstadt, Clemens Schöpf Institute of Organic Chemistry.