摘 要

在过去的几十年中，像Pb(Zr_xTi_1-x)O₃ (PZT) 、BaTiO₃这些铁电材料已经广泛应用在电子设备中，比如微波器件、电容器、铁电存储器等。但是由于存在Pb这一元素会严重污染环境，所以需要寻求环境友好的材料来代替PZT。BaTiO₃是一种无铅铁电材料，但是由于其较低的居里温度（T_c ≈ 120 °C)）而在高温范围内受到限期。因此需要寻找一种高居里温度的无铅铁电材料来适应极端环境。BaTi₂O₅ 材料是可在高温下使用的新型无铅铁电材料的有力候选者，在高居里温度 (T_c)下展现出高介电常数(ε_r) 和低介电损耗(tan δ)。在本论文中，通过溶胶-凝胶法来取代BaTi₂O₅ 薄膜中的Ti位，来研究其性能影响。主要内容如下：

1.通过溶胶 - 凝胶法在Pt（111）/ Ti / SiO₂/ Si衬底上制备了BaTi₂O₅薄膜。 研究了厚度（6,7,8,9层）和退火气氛（O₂，N₂）对BaTi₂O₅薄膜结构和物理性能的影响。在O₂中退火8层的BaTi₂O₅薄膜的介电常数最大为210。

2.通过溶胶-凝胶法在Pt（111）/ Ti / SiO₂ / Si衬底上制备了BaFe_xTi_2-xO₅（x = 0,0.004,0.008,0.02,0.02）薄膜。XRD和拉曼结果表明，BaFe_xTi_2-xO₅薄膜在BaTi₂O₅单相中，没有二次相的证据。Fe掺杂膜的介电常数高于于未掺杂膜的介电常数。x = 0.004的薄膜表现出明确的磁滞回线。

3.通过溶胶 - 凝胶法在Pt（111）/ Ti / SiO₂/ Si衬底上制备了BaNb_xTi_2-xO₅（x = 0.002,0.004,0.008,0.012）薄膜。XRD和拉曼结果表明，BaNb_xTi_2-xO₅薄膜在BaTi₂O₅单相中，没有二次相的证据。Nb掺杂膜的介电常数高于未掺杂膜。 Nb掺杂的膜表现出明确的磁滞回线。x = 0.008的膜的2Pr为2.4μC/ cm 2。

关键词：BaTi₂O₅薄膜，铁掺杂，铌掺杂，溶胶-凝胶法

Abstract

During the past decade ferroelectric materials, such as Pb(Zr_xTi_1-x)O₃ (PZT) and BaTiO₃, have been worldly used in electric and electronic devices, such as microwave devices, capacitors, ferroelectric access memories, etc.. However, the toxicity of Pb poses serious environment problems so that safe materials are need to substitute the hazardous PZT. BaTiO₃, lead-free ferroelectric materials, is limited in the high-temperature range due to its low Curie temperature (T_c ≈ 120 °C). Therefore, it is necessary to find a lead-free ferroelectric with high Curie temperature for extreme environments. BaTi₂O₅ material is a promising candidate for a new lead-free ferroelectric material at high temperature, exhibiting high dielectric permittivity (ε_r) and low dielectric loss (tan δ) at a high Curie temperature (T_c). In the peper, the effects of the preparation and substitution in Ti-site of BaTi₂O₅ thin films via sol-gel method. The main contents are as follows:

1. The BaTi₂O₅ thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates via sol-gel process. The effects of thickness (6, 7, 8, 9 layers) and annealing atmosphere (O₂, N₂) on the structure and physical properties of BaTi₂O₅ thin films were investigated. The BaTi₂O₅ thin films with 8 layers annealed in O₂ had the maximum dielectric permittivity of 210.

2. The BaFe_xTi_2-xO₅ (x = 0, 0.004, 0.008, 0.012, 0.02) thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates via sol-gel process. The XRD and Raman results indicated that the BaFe_xTi_2-xO₅ thin films were in BaTi₂O₅ single phase, with no evidence of a secondary phase. The dielectric permittivity of Fe-doped films was higher than that of un-doped film. The thin film with x = 0.004 exhibited well-defined hysteresis loops.

3. The BaNb_xTi_2-xO₅ (x = 0, 0.002, 0.004, 0.008, 0.012) thin films were prepared on Pt(111)/Ti/SiO₂/Si substrates via sol-gel process. The XRD and Raman results indicated that the BaFe_xTi_2-xO₅ thin films were in BaTi₂O₅ single phase, with no evidence of a secondary phase. The dielectric permittivity of Nb-doped films was higher than that of un-doped film. The Nb-doped films exhibited well-defined hysteresis loops. The 2P_r of the film with x = 0.008 was 2.4 μC/cm².

Keywords: BaTi₂O₅ thin films, Fe-doped, Nb-doped, sol-gel method

目录

摘 要 I

Abstract II

第1章 绪论 1

1.1 BaTi₂O₅铁电薄膜的研究背景与概况 1

1.1.1 铁电材料概述及其研究进展 1

1.1.2 铁电薄膜材料的合成技术 2

1.2 BaTi₂O₅材料的国内外研究现状 3

1.3 BaTi₂O₅的晶体结构及铁电性能 3

1.4 BaTi₂O₅铁电薄膜的应用 4

1.5 本文研究内容及其意义 5

第2章 BaTi2O5铁电薄膜的制备 6

2.1 化学药品与实验仪器 6

2.2 前驱体溶胶的配置 6

2.2.1 纯BaTi₂O₅前驱体溶胶 7

2.2.2 掺铁BaTi2O5前驱体溶胶 7

2.2.3 掺铌BaTi2O5前驱体溶胶 7

2.3 薄膜的制备 7

2.3.1 基片的准备与清洗 7

2.3.2 薄膜的涂覆及热处理过程 8

2.4 电极制备 8

2.5 薄膜的测试与表征 9

2.5.1 激光拉曼光谱分析 9

2.5.2 XRD图谱 9

2.5.3 薄膜的介电性能 9

2.5.4 薄膜的铁电性能 9

第3章 BaTi₂O₅薄膜的性能表征 10

3.1 薄膜制备实验条件 10

3.2 厚度对薄膜结构、性能的影响 10

3.3 退火氛围对薄膜结构、性能的影响 11

第4章 铁掺杂BaTi₂O₅薄膜的结构及其性能表征 13

4.1 薄膜结构 13

4.2 薄膜的介电性能 14

4.3 薄膜的铁电性能 14

第5章 铌掺杂BaTi₂O₅薄膜的结构及其性能表征 16

5.1 薄膜结构 16

5.2 薄膜的介电性能 16

5.3 薄膜铁电性能 17

第6章 总结 19

参考文献 20

致谢 22

第1章 绪论

在一定温度范围内，材料自身会发生自发极化且自发极化矢量的方向会随着外电场的改变而发生改变，我们称这种材料为铁电材料。在居里温度以下或附近时，铁电材料表现出良好的铁电性能，而当温度高于居里温度时，铁电体会失去铁电性而变成顺电体。自从1920年，法国人发现了罗息盐即酒石酸钾钠中存在奇特介电性能并提出了"铁电性"的概念后，人们便开始了大量的铁电体研究^[1]。由于在介电性、铁电性、压电性、电光特性、声光特性、非线性光学等方面具有优良特性，因此铁电材料在制备铁电动态随机存取存储器、薄膜型室温红外探测器、薄膜型压电马达、超声探测器、薄膜电容器和集成光波导器件等方面具备极大的优势。

如今，各种器件向着小型化，轻量化，集成化发展，而且现代材料合成工艺也在薄膜制备方面取得了重大进展。然而人们之前大多数采用的铅基材料如PbTiO₃（PTO）和PbZr_1-xTixO₃（PZT）虽然具有高介电常数和良好的压电和铁电性能而被广泛研究，但这些材料里面含有不环保元素Pb将导致环境问题，所以，对制备无铅的环境友好型铁电薄膜的研究具有重大意义。