鐵酸鉍極化工程

Abstract

BiFeO3 是目前能表現出兩種鐵素體排列的唯一單相材料 - 高於室溫的反鐵磁性 和鐵電性 [1]。此外，它還顯示出穩定的電磁耦合 - 由 Dzyaloshinskii-Moriya (DM)相互作用 述的反鐵磁自旋結構中的反對稱交換引起的弱鐵磁性。由於 這種優越的性能，BiFeO3 已成為多層次社會中最受歡迎和研究的材料[2] [3] [4] [5]。因此，不可避免地，控制和理解 BiFeO3 中的鐵電是這一領域的關鍵問題。 在本論文中，我將重點介紹 BiFeO3 薄膜中鐵電性的工程，並了解以下三個主要 現象背後的基本物理 - 鐵電與超導之間的接近效應，鐵電疇壁引起的異常微波 吸收和鐵電的作用在分水過程中發揮作用。本論文的第一部分回顧了背景知識和 歷史，為讀者 供了一個全面的了解，以便在以下章節中對內容有清晰的認識。 我將首先介紹鐵質訂單參數，鐵結構域和域牆，以及域牆工程。本論文的第二部 分致力於研究 YBa2Cu3O7-x 中各向異性超導體的周期性多鐵磁疇圖案，包括 109 °和 71°[6]型。 YBa2Cu3O7-x 中的各向異性超導性可以在 109°和 71°域上進 行觀察。本論文第三部分將討論通過微波阻抗顯微鏡探測的BiFeO3 71°域的異 常微波吸收。在這部分中，我將探討微波頻率範圍內 BiFeO3 的疇壁運動與空間 分辨率，闡明了疇壁的貢獻。最後，我將展示鐵電工程在水分解過程中的應用[7]。 這部分將著重於通過控制 BiFeO3 的自發極化方向和小面來了解鐵電體在水分離 過程中的作用。

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 .