【作者】 姜凯；

【导师】 胡志高；

【作者基本信息】 华东师范大学 ， 微电子学与固体电子学， 2014， 博士

【摘要】 无铅型铁电陶瓷材料由于其优良的铁电性能,对环境的友好性等,是当前铁电陶瓷材料的研究热点之一。目前,无铅型铁电材料的研究主要集中在：1)钙钛矿型钛酸盐系铁电材料,如钛酸钡BaTiO3(BT),钛酸锶SrTiO3(ST),钛酸锶钡(BaxSr1-x)TiO3(BST)等。2)钨青铜型的铌酸盐系铁电体,如铌酸锶钡SrxBa1-xNb2O6(SBN)等。3)含Aurivillius层状结构的铁电体。例如钛酸铋Bi4Ti3O12,铌酸锶铋SrBi2Nb209(SBNO)等。其中BST, SBN以及SBNO及其掺杂铁电材料具有较高电阻率、良好的抗疲劳特性、高介电常数等特点,在热释电探测器、紫外探测器、非制冷红外探测器、非制冷红外焦平面阵列和铁电存储等领域具有很大的应用前景。随着各行各业对高热释电、高介电可调性等性能材料的需求日益增加,无铅型铁电陶瓷的制备,性能及改性研究已成为铁电陶瓷材料的一个研究热点。根据目前科研工作者对铁电材料用于热释电探测器的工作原理的分析,热释电探测器的理想工作温度范围应在热释电材料的居里温度(Tc)点附近,这也就相应提高了探测器对环境温度的要求。所以降低这一类铁电材料的相变温度点是作为下一代热释电探测器开发的必要条件。因此,本论文采用光谱测量手段系统研究了无铅型铁电氧化物及其稀土元素掺杂的铁电材料如Ba0.4Sr0.6-xMnxTiO3(BSMT), SrxBa1-xNb2O6(SBN)和SrBi2Nb2-xNdxO9(SBNN)等陶瓷的合成、电子结构、光学声子振动模式及其居里温度特性的改善。本文的主要工作和创新点包括以下几点：一、研究了含铋层状结构铁电陶瓷SBNN在80-873K温度范围内的拉曼光谱,远红外光谱,以及椭圆偏振光谱。详细讨论钕元素Nd的掺杂对SBNN的电子结构,光学声子模式,以及居里温度的影响。对传统固态烧结反应制备的SrBi2Nb2-xNdxO9(0≤x≤0.20)研究表明,(a)通过对SBNN在80K的拉曼光谱分析得到,由Nb06氧八面体中产生的峰位在207cm-1的A1g[Nb]声子模式的频率随着Nd组分的增加而减少,随着温度的增加,A1g[Nb]声子模式的峰位及其强度在SBNN的铁电相到顺电相的相变温度附近都显示出不连续性。(b)通过Lorentz振子模型拟合SBNN在350-1500cm-1范围内的远红外反射光谱,我们发现5个红外活性的声子模式。由于Nd组分的增加导致的晶格畸变,Nb06倾斜和对称拉伸模式随着Nd组分的增加而减少。这和拉曼活性的声子振动模式的变化行为是一致的。通过拟合得到的高频介电常数在4.55到4.80之间,显示了Nd组分对远红外介电函数的影响。(c)通过在0°到500°变温椭圆偏振光谱,用Tauc-Lorentz色散模型拟合分析得到了SBNN的两个带间跃迁能量(在0°时跃迁能量分别为3.70和4.78eV)以及对应能量范围内的介电函数。在靠近铁电到顺电的相变温度时,这两个带间跃迁能量随着温度的升高都存在一个反常的变化。这种带间跃迁的变化是因为在晶格畸变过程中Bi6s和O2p轨道的杂化产生的。最后我们发现：在Bi202层中引入了Nd离子后,我们从Nb-O1-Nb的键角得到了Nb06氧八面体的倾斜角度,从9.7°减少到5.5°,进而减弱了Nb06氧八面体的扭曲程度,最后导致了的SBNN的居里温度随着Nd组分的增加,从710减少到550K。这对作为研究和开发下一代热释电红外探测器材料提供了科学依据。二、研究了钙钛矿型铁电陶瓷BSMT在紫外到远红外光子能量范围内的光学常数,禁带宽度等变化,并详细讨论Mn的掺杂对红外及拉曼声子模式,以及电子结构的影响。对传统固态烧结反应制备的Bao.4Sr0.6-xMnxTiO3(0.01≤x≤0.10)研究表明,(a) XRD分析结果表明,在1%至10%的Mn掺杂范围内,BSMT是单一的钙钛矿相,没有其他杂相的存在。(b)由于Ti06氧八面体随着Mn组分的增加而产生的畸变,拉曼活性的声子模式A1(LO3)/E(LO)的频率蓝移8cm-1。红外活性的T04声子模式的频率从532减少到520cm-1。(c)在1.0到3.0eV范围内,BSMT的介电函数ε2随Mn组分的增加而增加。光学禁带宽度(乓)在3.40到3.65eV之间,并且发现Eg随着Mn组分的增加而减少,需要指出的是在Mn则分增加到10%之后,ε2和Eg都有一个反常的变化。该研究为BSMT铁电陶瓷在新型光电多功能器件上的潜在应用提供了科学依据。三、研究了钨青铜型铁电陶瓷SBN的拉曼及红外活性的低频声子振动模式,得到其随着Sr组分以及温度的变化特性,观察到SBN的软模在相变点附近消失,由此得到SBN的居里温度随组分的变化关系。通过变温拉曼散射和傅里叶红外光谱技术探讨SrxBa1-xNb206(0.30≤x≤0.50)铁电陶瓷的异常晶格振动特性。(a)红外活性的的T2u。声子模式的频率随着Sr组分的增加,红移了大约2cm-1。原因是较大的Ba离子导致了铌八面体的变形。(b)从150到750K的变温拉曼光谱分析得到,随着温度的升高,Alg声子模式的频率向低频方向移动,强度明显降低,并且展宽明显变大。在居里温度点附近,A1g声子模式的频率和半高宽随温度变化的斜率均发生异常变化。SBN陶瓷的软模大约在42cm-1。随着温度的升高,软模的频率逐渐减少,耦合并最后消失。基于这些声子模式随温度的变化规律,我们得到SBN的居里温度与Sr组分之间的关系：Tc (x)=556-371x。更多还原

【Abstract】 Lead-free ferroelectric ceramic materials, owing to its excellent electrical properties and environmental friendliness, are one of the current hot researches of ferroelectric ceramic materials. At present, the lead-free ferroelectric research focuses on:1) the perovskite titanate ferroelectric materials, such as:barium titanate BaTiO3(BT), strontium titanate SrTiO3(ST), barium strontium titanate (BaxSr1-x) TiO3(BST), etc.2) type of tungsten bronze niobate ferroelectrics, such as strontium barium niobate SrxBa1-xNb2O6(SBN), etc.3) containing Aurivillius layer structure of ferroelectrics. Such as bismuth titanate Bi4Ti3O12, niobium acid strontium bismuth SrBi2Nb2O9(SBNO), etc. BST, SBN and SBNO and doping ferroelectric material with high resistivity, good fatigue resistance characteristic and high dielectric constant, pyroelectric detector, uv detector, uncooled infrared detectors, uncooled infrared focal plane arrays and ferroelectric memory, and other fields has great application prospect. With all walks of life to high heat release performance material such as electricity, high dielectric tunability of growing demand, type lead-free ferroelectric ceramic preparation, properties and modification studies has become a research hotspot of ferroelectric ceramic materials. According to the current scientific research workers of ferroelectric materials used for the analysis of the working principle of pyroelectric detector, the ideal working temperature scope of the pyroelectric detector should be in pyroelectric material near the Curie temperature (Tc), enhanced detector that is corresponding to the ambient temperature requirements. So to reduce this kind of phase change temperature point of ferroelectric material is as the next generation of pyroelectric detector development necessary conditions. Therefore, this paper systemly studies the type lead-free ferroelectric oxides and rare earth element doped ferroelectric materials such as Ba0.4Sr0.6-xMnxTiO3(BSMT), SrxBa1-xNb2O6(SBN) and SrBi2Nb2-xNdxO9(SBNN) and so on synthesis of ceramic, electronic structure and optical phonon vibration modes and the improvement of the Curie temperature characteristic using spectrometry measurements. In this paper, the main work and innovation points include the following:Ⅰ. The bismuth layer structure ferroelectric ceramics SBNN were studied in the temperature range of80-873K using Raman spectrum, infrared spectrum, and the ellipsometry spectroscopy. Detailed discussion in electronic band structure, optical phonon modes, and Curie temperature affected by the neodymium Nd doping in SBNN ceramics.The studies on SrBi2Nb2-xNdxO9(0≤x≤0.20) ceramics preparated by the solid state sintering reaction have shown that (a) Raman spectra analysis of SBNN at80K, The A1g[Nb] phonon mode located at207cm-1, origined from the octahedral NbO6oxygen, whose frequency increased with the increase of Nd components decreasing. With the increase of temperature, the peak position and strength of the A1g[Nb] phonon modes shows discontinuity in SBNN ceramics near the phase transition temperature.(b) The experimental spectra in the wavenumbers range of350-1500cm-1were analyzed using the Lorentz oscillator model for five infrared-active phononmode observed. It is found that the frequencies of the NbO6tilting and symmetric stretching modes linearly decrease with the Nd composition due to the octahedra distortion. The change of infrared-active phonon mode is consistent with the Raman-active behavior. The high frequency dielectric constant varies in the range from4.55to4.80, owing to the contribution from the stronger electronic transitions,(c) Base on the analysis on dielectric functions from0to500℃with Tauc-Lorentz dispersion model, the two interband transitions (located at3.70and4.78eV) have shown an abrupt variation near the phase transition region. The changes of dielectric functions are mainly due to the thermal-optical and/or photoelastic effect. Moreover, the characteristic alteration in interband transitions can be ascribed to distortion of NbO6octahedron and variation of hybridization between Bi6s and O2p states during the structure transformation. Finally, we found that the introduction of the rare ions in the Bi2O2layers can induce the tilting angle of NbO6octahedron obtained from Nb-O1-Nb bond angle, which decreases remarkably from9.7°for to5.5°. The phase transition temperature of SBNN ceramics decreases from about710to550K with increasing Nd composition, which provides a scientific basis for the development of the next generation of pyroelectric infrared detector materials.II. The dielectric functions of the perovskite ferroelectric BSMT ceramics in the photon energy range from ultraviolet to far-infrared have been investigated by the spectroscopy ellipsometry and infrared reflectance spectra. The lattice vibrations and electric band structure BSMT ceramics with different Mn doping composition are systematically studied.The Ba0.4Sr0.6-xMnxTiO3(BSMT) ceramics with different Mn composition (from1%to10%) have been prepared via the conventional solid-state reaction sintering,(a) The X-ray diffraction analysis shows that the ceramics are polycrystalline with the single perovskite phase.(b) The three first-order Raman-active phonon modes can be observed, and the frequency of the A1(LO3)/E(LO) mode shows a blue shift of8cm-1with the Mn composition, which can be attributed to the distortion of the TiO6octahedron. With increasing Mn composition, the frequency of the infrared-active TO4mode decreases from532to520cm-1, owing to the local variation of the lattice constant induced by the Mn incorporation,(c) The82increases with increasing Mn composition below5%, then sharply decreases at the Mn composition of10%in the photon energy range of1.0to3.0eV. It is found that the optical bandgap for the BSMT ceramics is varied between3.40and3.65eV with different Mn composition. A sharp increase of the Eg is observed when the Mn composition is10%. The present results could be crucial for future applications of ferroelectric-based optoelectronic devices. III. The Raman and infrared-active phonon modes in the low frequency range for the tungsten bronze ferroelectric SBN ceramics have been studies by temperature dependent Raman spectroscopy and infrared reflectance spectra. Form the soften and disppared of the A1g and soft mode, the Curie temperature of the SBN ceramics can be obtained as a function of Sr compositions.The lattice vibrational spectra of ferroelectric SrxBa1-xNb2O6(0.30≤x≤0.50) ceramics obtained by Ramna and infrared spectra can be affected by the variation of Sr/Ba ratios.(a) The frequency of IR-active T2u phonon mode decreases with increasing Sr composition, which can be ascribed to stronger deformation of the NbO6octahedra.(b) From the Raman analysis from150to750K, with increasing the temperature, the frequency of the A1g phonon mode decreases, the reduced intensity of the mode decreases as the temperature is increased. At the same time, the peak broadens with temperature. In general, a sharp change in the temperature dependence of both frequency and halfwidth of different Raman peaks was observed to occur at the phase transition. The soft modes of the SBN ceramics are located at about42cm-1. With increasing the temperature, the soft mode becomes soften, overdamped and disappeared. According to changes of the soft modes, it is clear that increasing Sr composition (from0.30to0.50) leads to the shrinking of T c (from450to375K) for phase transition:Tc (x)=556-371x.更多还原