Engineering the Ferroelectricity in BiFeO3

• Main Authors: Huang, Yen-Lin, 黃彥霖
• Other Authors: Chu, Ying-Hao
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/d9j6nu

博士 === 國立交通大學 === 材料科學與工程學系所 === 105 === BiFeO3 is the only single-phase material that exhibits two ferroic orderings – antiferromagnetism and ferroelectricity above room temperature[1]. Moreover, it also shows a robust magnetoelectric coupling – a weak ferromagnetism induced by the antisymmetric exchange in the antiferromagnetic spin structure described by the Dzyaloshinskii-Moriya (DM) interaction. Due to this superior property, BiFeO3 has become the most popular and studied material in multiferroic society[2][3][4][5]. Thus, inevitably, controlling and understanding the ferroelectricity in BiFeO3 are the crucial issues in this field. In this dissertation, I will focus on the engineering of ferroelectricity in BiFeO3 thin films and understanding the fundamental physics behind the following three major phenomena – the proximity effect between ferroelectricity and superconductivity, anomalous microwave absorption induced by ferroelectric domain wall, and the role of ferroelectricity plays in water splitting process. The first part of this dissertation reviews the background history and knowledge that will provide a comprehensive picture for readers to have clear ideas of the contents in the following chapters. I will begin with the introduction of ferroic order parameters, ferroic domain and domain wall, and domain wall engineering. The second part of this dissertation devotes to the study of anisotropic superconductivity in YBa2Cu3O7−x induced by periodic multiferroic domain patterns, including 109◦ and 71◦[6] patterns. The anisotropic superconductivity can be observed in YBa2Cu3O7−x on both 109◦ and 71◦ domain patterns. The third part of this dissertation will discuss the anomalous microwave absorption at 71 domain pattern of BiFeO3 probed by microwave impedance microscopy. In this part, I will explore the domain wall motion of BiFeO3 in microwave frequency regime with spatial resolution, which elucidates the contribution from the domain wall. Finally, I will demonstrate the application of ferroelectricity engineering in water splitting process[7]. This part will focus on understanding the role of ferroelectricity plays in the water splitting process via controlling the spontaneous polarization direction and the facets of BiFeO3 .