本論文目的為製備高磁電轉換效率之磁電複合塊材。磁電複合材料是由壓電相與鐵電相組成，本實驗選擇CoFe2O4 (CFO)作為鐵磁相與K0.5Na0.5NbO3 (KNN)作為鐵電相，並利用兩種方法試圖提高磁電耦合的響應值，第一種方法會透過摻雜提升鐵磁相與鐵電相的性質；第二種方法為鑲嵌鐵電相與鐵磁相在第三相中，避免介面的化學反應。
在第一種方法中，會分別先燒結好鐵磁相與鐵電相粉末，CFO與摻雜Ti之CFO，即Co1.2Fe1.6Ti0.2O4 (CTFO)會在1200 ℃燒結，KNN與摻雜Li之KNN，即 (K0.5Na0.5)0.96Li0.04NbO3 (KLNN)會在1100 ℃燒結，接著會將兩相均勻混合後，在1100 ℃下進行燒結，合成各種磁電複合物，即CFO-KNN，CTFO-KNN，CFO-KLNN及CTFO-KLNN，透過X射線繞射儀鑑定其相純度，並確認無二次相的生成。
在第二種方法中，則會透過低溫熱壓的方式來製備試片。同樣會先燒結CFO與KNN粉末，接著與第三相材料PVDF均勻混合後，在160 ℃及高壓(150 MPa)環境下合成實驗所需的試片。根據X光繞射圖可以看到試片是由鐵磁相與鐵電相組合而成，但PVDF因其結晶性較低，需透過FTIR來確認其存在。
實驗量測顯示，摻雜對於複合物之磁電效應都有提升的趨勢，CTFO-KNN複合物相對於CFO-KNN，可以在較低偏壓磁場下達到最高磁電係數，且磁電響應峰值有增加的情況。也可以看到隨著Li的摻雜，複合物CFO-KLNN相對於CFO-KNN之磁電效應有著明顯的提升，但CTFO-KLNN在鐵磁相與鐵電相都摻雜元素後，其磁電峰值反而下降，並且有兩個峰的出現。
鐵磁相與鐵電相鑲嵌於PVDF之複合物，磁電響應量測結果發現，其磁電效應值比起CFO-KNN複合物降低了許多。從微結構來看，雖然PVDF有效隔絕了CFO與KNN，但因為在低溫的情況下熱壓，且沒有抽真空，導致試片密度不高並有著許多的孔洞，使兩相之間的應力無法傳遞，造成磁電係數的下降。

In this study, CoFe2O4-K0.5Na0.5NbO3 (CFO-KNN), a magnetoelectric (ME) composite, was synthesized following the solid-state sintering method. Chemical doping of the components by Ti and Li, as well as embedding of the components in a third phase (i.e. PVDF) were carried out to increase magnetoelectric effect. The composition and microstructure of the obtained composites were examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD patterns indicated that the composites, both embedded in PVDF and doped with Ti and Li, showed no evidence of a secondary phase. The Ti and Li doping did not result in a notable change in the microstructure of sintered composites. SEM micrographs revealed that the embedded composites were indeed isolated by PVDF. However, the ME voltage coefficient (αE) measured with the embedded composites was very low, owing to a high porosity of the samples hot-pressed at low temperature (160 ℃). The composites composed of KNN and Ti-doped CFO (i.e. KNN-CTFO) showed higher αE than undoped KNN-CFO, with its peak value appearing at a lower DC magnetic bias field. A further enhancement in αE was achieved with the composites composed of Li doped KNN and CFO (i.e. KLNN-CFO). In addition, the dielectric properties of the composites were studied. The results indicated that the dielectric responses in both the doped and embedded composites were dominated by the Maxwell-Wagner effect.

[1] Y. Wang, J. Hu, Y. Lin, and C.-W. Nan, "Multiferroic magnetoelectric composite nanostructures." NPG Asia Materials, 2, 2, 61-68, (2010).
[2] Y. Wang et al., "An extremely low equivalent magnetic noise magnetoelectric sensor." Advanced materials, 23, 35, 4111-4114, (2011).
[3] J. Ma, Z. Shi, and C. W. Nan, "Magnetoelectric properties of composites of single Pb (Zr, Ti) O3 rods and terfenol‐D/epoxy with a single‐period of 1‐3‐type structure." Advanced materials, 19, 18, 2571-2573, (2007).
[4] K. H. Lam, C. Lo, and H. L. Chan, "Frequency response of magnetoelectric 1–3-type composites." Journal of Applied Physics, 107, 9, 093901, (2010).
[5] R. A. Islam, C.-b. Rong, J. Liu, and S. Priya, "Effect of gradient composite structure in cofired bilayer composites of Pb (Zr 0.56 Ti 0.44) O 3–Ni 0.6 Zn 0.2 Cu 0.2 Fe 2 O 4 system on magnetoelectric coefficient." Journal of Materials Science, 43, 18, 6337-6343, (2008).
[6] R. A. Islam, Y. Ni, A. G. Khachaturyan, and S. Priya, "Giant magnetoelectric effect in sintered multilayered composite structures." Journal of Applied Physics, 104, 4, 044103, (2008).
[7] R. A. Islam, V. Bedekar, N. Poudyal, J. P. Liu, and S. Priya, "Magnetoelectric properties of core-shell particulate nanocomposites." Journal of Applied Physics, 104, 10, 104111, (2008).
[8] M. Liu and N. X. Sun, "Voltage control of magnetism in multiferroic heterostructures." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 372, 2009, 20120439, (2014).
[9] J. P. Praveen, V. R. Monaji, E. Chandrakala, S. Indla, V. Subramanian, and D. Das, "Enhanced magnetoelectric coupling in Ti and Ce substituted lead free CFO-BCZT laminate composites." Journal of alloys and compounds, 750, 392-400, (2018).
[10] P. Chin Goh, K. Yao, and Z. Chen, "Lithium diffusion in (Li, K, Na) NbO3 piezoeletric thin films and the resulting approach for enhanced performance properties." Applied Physics Letters, 99, 9, 092902, (2011).
[11] K. H. J. Buschow and F. R. Boer, "Physics of magnetism and magnetic materials. Springer2003).
[12] D. Shi, "Functional thin films and functional materials: new concepts and technologies. 清华大学出版社有限公司2003).
[13] J. C. Burfoot and G. W. Taylor, "Polar dielectrics and their applications. Univ of California Press1979).
[14] K. C. Kao, "Dielectric phenomena in solids. Elsevier2004).
[15] J. R. Macdonald and E. Barsoukov, "Impedance spectroscopy: theory, experiment, and applications." History, 1, 8, 1-13, (2005).
[16] P. Curie, "Sur la symétrie dans les phénomènes physiques, symétrie d'un champ électrique et d'un champ magnétique." Journal de physique théorique et appliquée, 3, 1, 393-415, (1894).
[17] L. D. Landau, J. Bell, M. Kearsley, L. Pitaevskii, E. Lifshitz, and J. Sykes, "Electrodynamics of continuous media. elsevier2013).
[18] D. Astrov, "The magnetoelectric effect in antiferromagnetics." Sov. Phys. JETP, 11, 3, 708-709, (1960).
[19] G. Rado and V. Folen, "Observation of the magnetically induced magnetoelectric effect and evidence for antiferromagnetic domains." Physical review letters, 7, 8, 310, (1961).
[20] M. Fiebig, "Revival of the magnetoelectric effect." Journal of Physics D: Applied Physics, 38, 8, R123, (2005).
[21] S. Naifar, S. Bradai, C. Viehweger, and O. Kanoun, "Survey of electromagnetic and magnetoelectric vibration energy harvesters for low frequency excitation." Measurement, 106, 251-263, (2017).
[22] E. Ascher and A. G. M. Janner, "Upper bounds on the magneto-electric susceptibility." Physics Letters A, 29, 6, 295, (1969).
[23] V. Wadhawan, "Introduction to ferroic materials. CRC press2000).
[24] G. Smolenskiĭ and I. Chupis, "Ferroelectromagnets." Soviet Physics Uspekhi, 25, 7, 475, (1982).
[25] N. A. Hill, "Why are there so few magnetic ferroelectrics?" The journal of physical chemistry B, 104, 29, 6694-6709, (2000).
[26] E. Bertaut and M. Mercier, "Structure magnetique de MnYO3." Physics Letters, 5, 1, (1963).
[27] E. Ascher, H. Rieder, H. Schmid, and H. Stössel, "Some properties of ferromagnetoelectric nickel‐iodine boracite, Ni3B7O13I." Journal of Applied Physics, 37, 3, 1404-1405, (1966).
[28] T. Kimura, T. Goto, H. Shintani, K. Ishizaka, T.-h. Arima, and Y. Tokura, "Magnetic control of ferroelectric polarization." nature, 426, 6962, 55-58, (2003).
[29] B. D. Tellegen, "The gyrator, a new electric network element." Philips Res. Rep, 3, 2, 81-101, (1948).
[30] J. Van Suchtelen, "Product properties: a new application of composite materials." Phillips Research Reports, 27, 28-37, (1972).
[31] J. Van den Boomgaard, D. Terrell, R. Born, and H. Giller, "An in situ grown eutectic magnetoelectric composite material." Journal of Materials Science, 9, 10, 1705-1709, (1974).
[32] A. Van Run, D. Terrell, and J. Scholing, "An in situ grown eutectic magnetoelectric composite material." Journal of Materials Science, 9, 10, 1710-1714, (1974).
[33] N. Ortega, A. Kumar, J. Scott, and R. S. Katiyar, "Multifunctional magnetoelectric materials for device applications." Journal of Physics: Condensed Matter, 27, 50, 504002, (2015).
[34] K. Raidongia, A. Nag, A. Sundaresan, and C. Rao, "Multiferroic and magnetoelectric properties of core-shell CoFe 2 O 4@ BaTiO 3 nanocomposites." Applied Physics Letters, 97, 6, 062904, (2010).
[35] M. Liu et al., "Synthesis of ordered arrays of multiferroic Ni Fe 2 O 4-Pb (Zr 0.52 Ti 0.48) O 3 core-shell nanowires." Applied Physics Letters, 90, 15, 152501, (2007).
[36] J. S. Andrew, J. D. Starr, and M. A. Budi, "Prospects for nanostructured multiferroic composite materials." Scripta Materialia, 74, 38-43, (2014).
[37] S. Xie, F. Ma, Y. Liu, and J. Li, "Multiferroic CoFe 2 O 4–Pb (Zr 0.52 Ti 0.48) O 3 core-shell nanofibers and their magnetoelectric coupling." Nanoscale, 3, 8, 3152-3158, (2011).
[38] S. Xie, J. Li, Y. Liu, L. Lan, G. Jin, and Y. Zhou, "Electrospinning and multiferroic properties of NiFe 2 O 4–Pb (Zr 0.52 Ti 0.48) O 3 composite nanofibers." Journal of Applied Physics, 104, 2, 024115, (2008).
[39] Y. Chen et al., "Quasi-one-dimensional miniature multiferroic magnetic field sensor with high sensitivity at zero bias field." Applied Physics Letters, 99, 4, 042505, (2011).
[40] S. Dong, J. Zhai, J. Li, and D. Viehland, "Near-ideal magnetoelectricity in high-permeability magnetostrictive/piezofiber laminates with a (2-1) connectivity." Applied Physics Letters, 89, 25, 252904, (2006).
[41] S. Dong, J. Zhai, Z. Xing, J. Li, and D. Viehland, "Giant magnetoelectric effect (under a dc magnetic bias of 2 Oe) in laminate composites of FeBSiC alloy ribbons and Pb (Zn 1∕ 3, Nb 2∕ 3) O 3–7% Pb Ti O 3 fibers." Applied Physics Letters, 91, 2, 022915, (2007).
[42] M. Feng et al., "Optimizing direct magnetoelectric coupling in Pb (Zr, Ti) O3/Ni multiferroic film heterostructures." Applied Physics Letters, 106, 7, 072901, (2015).
[43] S. M. Gillette et al., "Effects of intrinsic magnetostriction on tube-topology magnetoelectric sensors with high magnetic field sensitivity." Journal of Applied Physics, 115, 17, 17C734, (2014).
[44] H. Greve, E. Woltermann, H.-J. Quenzer, B. Wagner, and E. Quandt, "Giant magnetoelectric coefficients in (Fe 90 Co 10) 78 Si 12 B 10-AlN thin film composites." Applied Physics Letters, 96, 18, 182501, (2010).
[45] R. A. Islam, H. Kim, S. Priya, and H. Stephanou, "Piezoelectric transformer based ultrahigh sensitivity magnetic field sensor." Applied Physics Letters, 89, 15, 152908, (2006).
[46] R. C. Kambale et al., "Colossal magnetoelectric response of PZT thick films on Ni substrates with a conductive LaNiO3 electrode." Journal of Physics D: Applied Physics, 46, 9, 092002, (2013).
[47] S. Mandal, G. Sreenivasulu, V. Petrov, and G. Srinivasan, "Magnetization-graded multiferroic composite and magnetoelectric effects at zero bias." Physical Review B, 84, 1, 014432, (2011).
[48] R. Martínez, A. Kumar, R. Palai, G. Srinivasan, and R. Katiyar, "Observation of strong magnetoelectric effects in Ba0. 7Sr0. 3TiO3/La0. 7Sr0. 3MnO3 thin film heterostructures." Journal of Applied Physics, 111, 10, 104104, (2012).
[49] A. McDannald, M. Staruch, G. Sreenivasulu, C. Cantoni, G. Srinivasan, and M. Jain, "Magnetoelectric coupling in solution derived 3-0 type PbZr0. 52Ti0. 48O3: xCoFe2O4 nanocomposite films." Applied Physics Letters, 102, 12, 122905, (2013).
[50] K. Mori and M. Wuttig, "Magnetoelectric coupling in Terfenol-D/polyvinylidenedifluoride composites." Applied Physics Letters, 81, 1, 100-101, (2002).
[51] S. S. Nair, G. Pookat, V. Saravanan, and M. Anantharaman, "Lead free heterogeneous multilayers with giant magneto electric coupling for microelectronics/microelectromechanical systems applications." Journal of Applied Physics, 114, 6, 064309, (2013).
[52] H. Palneedi et al., "Enhanced off-resonance magnetoelectric response in laser annealed PZT thick film grown on magnetostrictive amorphous metal substrate." Applied Physics Letters, 107, 1, 012904, (2015).
[53] C.-S. Park, K.-H. Cho, M. A. Arat, J. Evey, and S. Priya, "High magnetic field sensitivity in Pb (Zr, Ti) O 3–Pb (Mg 1/3 Nb 2/3) O 3 single crystal/Terfenol-D/Metglas magnetoelectric laminate composites." Journal of Applied Physics, 107, 9, 094109, (2010).
[54] C.-S. Park, A. Khachaturyan, and S. Priya, "Giant magnetoelectric coupling in laminate thin film structure grown on magnetostrictive substrate." Applied Physics Letters, 100, 19, 192904, (2012).
[55] M. Silva et al., "Optimization of the magnetoelectric response of poly (vinylidene fluoride)/epoxy/vitrovac laminates." ACS applied materials & interfaces, 5, 21, 10912-10919, (2013).
[56] G. Sreenivasulu, L. Fetisov, Y. Fetisov, and G. Srinivasan, "Piezoelectric single crystal langatate and ferromagnetic composites: Studies on low-frequency and resonance magnetoelectric effects." Applied Physics Letters, 100, 5, 052901, (2012).
[57] G. Srinivasan, E. Rasmussen, J. Gallegos, R. Srinivasan, Y. I. Bokhan, and V. Laletin, "Magnetoelectric bilayer and multilayer structures of magnetostrictive and piezoelectric oxides." Physical Review B, 64, 21, 214408, (2001).
[58] K. Tahmasebi, A. Barzegar, J. Ding, T. Herng, A. Huang, and S. Shannigrahi, "Magnetoelectric effect in Pb (Zr0. 95Ti0. 05) O3 and CoFe2O4 heteroepitaxial thin film composite." Materials & Design, 32, 4, 2370-2373, (2011).
[59] M. V. Ramanaa, N. R. Reddy, G. Sreenivasulu, B. Murty, and V. Murthy, "Enhanced mangnetoelectric voltage in multiferroic particulate Ni0. 83Co0. 15Cu0. 02Fe1. 9O4− δ/PbZr0. 52Ti0. 48O3 composites–dielectric, piezoelectric and magnetic properties." Current Applied Physics, 9, 5, 1134-1139, (2009).
[60] Y. Wang et al., "Lead-free magnetoelectric laminated composite of Mn-doped Na0. 5Bi0. 5TiO3–BaTiO3 single crystal and Tb0. 3Dy0. 7Fe1. 92 alloy." Journal of alloys and compounds, 496, 1-2, L4-L6, (2010).
[61] N. Zhang, J. Fan, X. Rong, H. Cao, and J. Wei, "Magnetoelectric effect in laminate composites of Tb 1− x Dy x Fe 2− y and Fe-doped BaTiO 3." Journal of Applied Physics, 101, 6, 063907, (2007).
[62] C. Fang et al., "Significant reduction of equivalent magnetic noise by in-plane series connection in magnetoelectric Metglas/Mn-doped Pb (Mg1/3Nb2/3) O3-PbTiO3 laminate composites." Journal of Physics D: Applied Physics, 48, 46, 465002, (2015).
[63] D. Gun Lee et al., "Ultra-sensitive magnetoelectric microcantilever at a low frequency." Applied Physics Letters, 101, 18, 182902, (2012).
[64] Y. Zhang, Z. Li, C. Deng, J. Ma, Y. Lin, and C.-W. Nan, "Demonstration of magnetoelectric read head of multiferroic heterostructures." Applied Physics Letters, 92, 15, 152510, (2008).
[65] J. Ryu et al., "Ubiquitous magneto-mechano-electric generator." Energy & Environmental Science, 8, 8, 2402-2408, (2015).
[66] A. Miszczyk and K. Darowicki, "Study of anticorrosion and microwave absorption properties of NiZn ferrite pigments." Anti-Corrosion Methods and Materials, (2011).
[67] L. Egerton and D. M. Dillon, "Piezoelectric and dielectric properties of ceramics in the system potassium—sodium niobate." Journal of the American Ceramic Society, 42, 9, 438-442, (1959).
[68] A. Safari and M. Abazari, "Lead-free piezoelectric ceramics and thin films." IEEE transactions on ultrasonics, ferroelectrics, and frequency control, 57, 10, 2165-2176, (2010).
[69] M. Ahtee and A. Hewat, "Structural phase transitions in sodium–potassium niobate solid solutions by neutron powder diffraction." Acta Crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography, 34, 2, 309-317, (1978).
[70] S.-S. Kim, S.-I. Na, J. Jo, D.-Y. Kim, and Y.-C. Nah, "Plasmon enhanced performance of organic solar cells using electrodeposited Ag nanoparticles." Applied Physics Letters, 93, 7, 305, (2008).
[71] M. Ahtee and A. Glazer, "Lattice parameters and tilted octahedra in sodium–potassium niobate solid solutions." Acta Crystallographica Section A: Crystal Physics, Diffraction, Theoretical and General Crystallography, 32, 3, 434-446, (1976).
[72] K. Wang and J.-F. Li, "Analysis of crystallographic evolution in (Na, K) Nb O 3-based lead-free piezoceramics by x-ray diffraction." Applied Physics Letters, 91, 26, 262902, (2007).
[73] J. Gregorio, Rinaldo and M. Cestari, "Effect of crystallization temperature on the crystalline phase content and morphology of poly (vinylidene fluoride)." Journal of Polymer Science Part B: Polymer Physics, 32, 5, 859-870, (1994).
[74] J. Wu et al., "Magnetic field induced formation of ferroelectric β phase of poly (vinylidene fluoride)." Applied Physics A, 126, 8, 1-6, (2020).
[75] M. M. Kumar, A. Srinivas, S. Suryanarayana, G. Kumar, and T. Bhimasankaram, "An experimental setup for dynamic measurement of magnetoelectric effect." Bulletin of Materials Science, 21, 3, 251-255, (1998).
[76] D. L.-I. Amplifier, "MODEL SR830." Interface, 4, 24, (1993).
[77] R. Gregorio, M. Cestari, and F. Bernardino, "Dielectric behaviour of thin films of β-PVDF/PZT and β-PVDF/BaTiO 3 composites." Journal of Materials Science, 31, 11, 2925-2930, (1996).
[78] M. Kobayashi, K. Tashiro, and H. Tadokoro, "Molecular vibrations of three crystal forms of poly (vinylidene fluoride)." Macromolecules, 8, 2, 158-171, (1975).