本研究主要探討鐵電材料的光伏打特性，由於其產生的光電壓可以大於材料本身的能隙，與半導體的光伏打效應有所不同，半導體產生的光電壓不會超過p-n接面之間的能障，故有其研究的價值。但由於鐵電材料普遍為絕緣體，其電阻很大，本實驗旨在透過摻雜改善材料的導電度，並利用固相合成法簡便且易於合成之特性，製備摻雜鈦或鉬之鈮酸鉀(KNbO3:Ti/Mo)多晶塊材，觀察其極化後的光電特性。
經X射綫繞射觀察，將無摻雜之鈮酸鉀於燒結溫度800~1010°C持溫20分鐘皆可得到純相鈮酸鉀，而摻雜鈦和鉬之鈮酸鉀在燒結溫度1000°C分別持溫8和10小時可得到純相，當摻雜濃度到10%以上時，會產生第二相。摻雜鈦之鈮酸鉀在室溫下的電阻率約為7.04x108 ohm-cm，比無摻雜之鈮酸鉀(7.82x109 ohm-cm)小了約一個數量級，而摻雜鉬之鈮酸鉀，其電阻率則比無摻雜之鈮酸鉀略有增加。將試片量測其介電常數隨溫度變化之趨勢，發現摻雜鉬及鈦之鈮酸鉀的居禮溫度比無摻雜之鈮酸鉀降低約20~30°C。將試片進行極化，並嘗試不同的極化溫度、電壓及時間，以達到最佳極化效果，接著將極化之試片量測其電流-電壓綫。經實驗證實，在適當的燒結和極化條件下，所得試片可以觀察到開路電壓，照光前後有明顯的電流變化。無摻雜之鈮酸鉀在照光後並無明顯之電流增加，顯示其缺乏可被光激發的電荷載子，而摻雜鈦及鉬之鈮酸鉀在照光後之光電流均比無照光多1~2個數量級，且照光後之開路電壓均有小幅提升。

The aim of this study was to search for ferroelectric photovoltaic materials. Because ferroelectric materials usually have a very high DC resistivity over 108 ohm-cm, there is a need to increase the mobile carrier concentration in these materials. For such a purpose, KNbO3 was doped with different ions in this study. Polycrystalline samples of KNbO3:M (M=Ti and Mo) were prepared by the solid-state reaction method. X-ray diffraction showed that a pure phase of Ti or Mo doped KNbO3 could be obtained after sintering at 1000 C for 8 and 10 hours, respectively, and the doping limit was below 10 at.%, above which secondary phases occurred. The Currie temperature of KNbO3 was reduced by 20~30 C by the doping. The resistivity of KNbO3:5%Ti was measured to be 7.04108 ohm-cm, an order of magnitude smaller than the un-doped KNbO3 (7.82109 ohm-cm), whereas the Mo doped samples showed a slightly higher resistivity than the un-doped KNbO3. After electrical poling in a high field, the current-voltage curves of the samples were measured with and without light irradiation. For the un-doped KNbO3 there was virtually no change in the output current before and after the illumination, indicating a lack of the carriers that could be activated by the light. However, both Ti and Mo doped KNbO3 showed an order of magnitude increase in the output current after the illumination.

[1] B. Matthias, A. von Hippel, Domain Structure and Dielectric Response of Barium Titanate Single Crystals, Physical Review, 73 (1948) 1378-1384.
[2] T. Shimada, T. Kitamura, Multi-Physics Properties in Ferroelectric Nanowires and Related Structures from First-Principles, 2010.
[3] M. Grundmann, The Physics of Semiconductors, Graduate Texts in Physics, Springer Berlin Heidelberg, 2010.
[4] 呂正傑, 詹世雄, 鐵電記憶體簡介, 奈米通訊, 5 (1998).
[5] W.D.C. Jr., D.G. Rethwisch, Materials Science and Engineering: An Introduction John Wiley and Sons, 2009.
[6] S. Nayak, B. Sahoo, T.K. Chaki, D. Khastgir, Facile preparation of uniform barium titanate (BaTiO3) multipods with high permittivity: impedance and temperature dependent dielectric behavior, RSC Advances, 4 (2014) 1212-1224.
[7] W.D. Kingery, H.K. Bowen, D.R. Uhlmann, Introduction to ceramics, John Wiley and Sons, New York.
[8] M. Qin, K. Yao, Y.C. Liang, High efficient photovoltaics in nanoscaled ferroelectric thin films, Applied Physics Letters, 93 (2008) .
[9] B. Jaffe, W.R. Cook Jr, H. Jaffe, Piezoelectric Ceramics, Academic Press, 1971.
[10] O. Muller, R. Roy, The Major Ternary Structural Families, Springer-Verlag, New York, 1974.
[11] C.G. Bergeron, S.H. Risbud, Introduction to Phase Equilibria in Ceramics, The American Ceramic Society Inc., Columbus, Ohio, 1984.
[12] W.-H. Lee, W.A. Groen, H. Schreinemacher, D. Hennings, Dysprosium Doped Dielectric Materials for Sintering in Reducing Atmospheres, Journal of Electroceramics, 5 (2000) 31-36.
[13] D.F.K. Hennings, Dielectric materials for sintering in reducing atmospheres, Journal of the European Ceramic Society, 21 (2001) 1637-1642.
[14] K.M. Nair, A.S. Bhlla, Advances in dielectric ceramic materials the American Ceramic Society, 88 (1998).
[15] 林麗娟, x光繞射原理及其應用, 工業材料, 1994.
[16] A.S. Bhalla, R. Guo, R. Roy, The perovskite structure – a review of its role in ceramic science and technology, Mat Res Innovat, 4 (2000) 3-26.
[17] S.-Y. Chu, K. Uchino, Photostrictive effect in Plzt-Based ceramics and its applications, Ferroelectrics, 174 (1995) 185-196.
[18] K. Uchino, M. Aizawa, L.S. Nomura, Photostrictive effect in (Pb, La) (Zr, Ti)O3, Ferroelectrics, 64 (1985) 199-208.
[19] K. Nonaka, M. Akiyama, T. Hagio, A. Takase, Effect of Pb/(Zr+Ti) molar ratio on the photovoltaic properties of lead zirconate-titanate ceramics, Journal of the European Ceramic Society, 19 (1999) 1143-1148.
[20] K. Nonaka, M. Akiyama, T. Hagio, A. Takase, Effect of multiple impurity doping on the photovoltaic properties of lead zirconate-titanate ceramics, Ferroelectrics, 223 (1999) 357-364.
[21] Y.S. Yang, S.J. Lee, S. Yi, B.G. Chae, S.H. Lee, H.J. Joo, M.S. Jang, Schottky barrier effects in the photocurrent of sol–gel derived lead zirconate titanate thin film capacitors, Applied Physics Letters, 76 (2000) 774-776.
[22] L. Pintilie, I. Vrejoiu, G. Le Rhun, M. Alexe, Short-circuit photocurrent in epitaxial lead zirconate-titanate thin films, Journal of Applied Physics, 101 (2007) -.
[23] P.S. Brody, High voltage photovoltaic effect in barium titanate and lead titanate-lead zirconate ceramics, Journal of Solid State Chemistry, 12 (1975) 193-200.
[24] N. Kazuhiro, A. Morito, X. Chao-Nan, H. Tsuyoshi, K. Masahiro, T. Akira, Enhanced Photovoltaic Response in Lead Lanthanum Zirconate-Titanate Ceramics with A-Site Deficient Composition for Photostrictor Application, Japanese Journal of Applied Physics, 39 (2000) 5144.
[25] K. Koumoto, L.M. Sheppard, H. Matsubara, Ceramic transactions: Mass and charge transport in ceramics. Volume 71, (1996).