本文選題：鈣鈦礦結(jié)構(gòu)　切入點(diǎn)：橢圓偏振光譜　出處：《華東師范大學(xué)》2015年博士論文

【摘要】：鐵電氧化物是一類重要的信息功能材料體系,被廣泛應(yīng)用在數(shù)據(jù)存儲(chǔ)和光電探測(cè)等領(lǐng)域,其中鈣鈦礦鐵電材料,特別是多鐵鐵酸鉍薄膜在室溫下同時(shí)具有鐵電性和反鐵磁性,具有良好的磁電耦合、高極化率和光伏效應(yīng)。此外,鐵電陶瓷[PbZZr1-xTixO3(PZT), PbSc1/2Ta1/2O3(PST)等]作為新型的功能材料具有介電常數(shù)高、介電損耗低,壓電和熱釋電性能良好等優(yōu)點(diǎn),使得它在高密度信息存儲(chǔ),高速處理,光電子技術(shù)以及通訊軍事領(lǐng)域有著廣闊的應(yīng)用前景,而這些相關(guān)功能器件的研發(fā)跟對(duì)該特征材料體系的認(rèn)識(shí)有密切的關(guān)系。通過(guò)調(diào)節(jié)脈沖激光沉積中不同的生長(zhǎng)條件,改變襯底,調(diào)整Zr/Ti組分和摻雜可以進(jìn)一步研究其內(nèi)部復(fù)雜的物理特性,比如相變,大部分的相變物理機(jī)制是基于x射線衍射微觀結(jié)構(gòu)表征和介電頻譜,電子能帶結(jié)構(gòu)和電子躍遷等信息是缺失的。因此鐵電材料的物理性質(zhì)研究在信息科學(xué)領(lǐng)域備受關(guān)注。光譜學(xué)手段是可用于材料表征的非破壞性探測(cè)技術(shù),通過(guò)光譜分析,可以獲得材料的光學(xué)常數(shù),晶格振動(dòng),電子能帶結(jié)構(gòu)以及電子躍遷等重要信息。當(dāng)材料處于變溫條件下,可以了解聲子行為和帶間躍遷能量在相變中的演化規(guī)律,研究材料的相變物理機(jī)制,為研究相變材料的物理特性開(kāi)辟嶄新而有效的途徑。本文的主要工作和創(chuàng)新點(diǎn)包括以下幾點(diǎn)：1.研究了脈沖激光沉積法中激光功率,氧分壓和薄膜壓應(yīng)力對(duì)鐵酸鉍薄膜晶格振動(dòng),光電躍遷,介電函數(shù)的影響。BFO聲子頻率隨激光功率的增加而略微增大,禁帶寬度隨著氧分壓的降低而減小。通過(guò)變溫拉曼光譜和紫外-近紅外透射光譜,發(fā)現(xiàn)A1(TO)聲子頻率和帶隙隨著溫度的升高而變小。采用脈沖激光方法在c軸藍(lán)寶石襯底上制備了不同激光功率下的BiFeO3薄膜。隨著激光功率的增加,晶格常數(shù)c/a值變小,Bi/Fe組分比降低。位于219,172,142 cm-1的A1橫向聲子模式的頻率隨著溫度的升高向低波數(shù)段移動(dòng),這是因?yàn)闊崤蛎?熱無(wú)序和晶格的非諧效應(yīng)。在200,500和640 K,低頻Raman聲子頻率出現(xiàn)異常,這分別對(duì)應(yīng)于磁相變,鐵電序不同態(tài)間的變化和G-型反鐵磁相變。激光功率造成Bi的缺失,Bi-O鍵長(zhǎng)度和強(qiáng)度的變化以及Fe06八面體局部結(jié)構(gòu)的畸變,使得E(TO)和A1(TO)聲子頻率略微增大。通過(guò)洛倫茲多振子模型擬合紅外反射光譜得到50-8000cm-1范圍內(nèi)的介電函數(shù),透明區(qū)介電函數(shù)隨激光功率的變化與堆積密度,表面粗糙度和缺陷態(tài)有關(guān)。在藍(lán)寶石襯底上不同氧分壓條件下制備了BFO薄膜,隨著氧分壓的增加,拉曼活性E(TO1)聲子頻率從74增為76 cm-1,與薄膜中的拉應(yīng)力有關(guān)。Fe2+離子和氧空位的濃度均隨著氧分壓的降低而增加。用Tauc-Lorentz色散模型擬合0.47-6.5 eV透射光譜得到介電函數(shù)。吸收邊隨著溫度的升高(8-300 K)呈現(xiàn)紅移趨勢(shì)。禁帶寬度Eg隨著溫度的升高而降低,與BFO薄膜中原子間距離影響的電子與聲子相互作用有關(guān)。在8K時(shí),隨著氧分壓的減小,Eg從2.88降為2.78 eV,這是由氧空位的增加在導(dǎo)帶和價(jià)帶之間形成的雜質(zhì)態(tài)引起的。通過(guò)在襯底LaAl03上沉積不同厚度的BFO薄膜來(lái)調(diào)節(jié)薄膜中的壓應(yīng)力。薄膜均是高度(111)擇優(yōu)取向的,隨著厚度的增加,壓應(yīng)變減小,薄膜與塊狀晶體之間的應(yīng)變比計(jì)算為1.75,1.57和1。壓應(yīng)變促使Eg由2.7減小為2.65 eV,電荷轉(zhuǎn)移躍遷能量由3.5增為4.1 eV。這與O2p態(tài)的移動(dòng)和局部Fe3+晶體場(chǎng)的變化有關(guān)。2.研究了(1-x)PST-xPbHfO3(0≤x≤0.2)弛豫陶瓷的介電函數(shù)隨溫度的變化關(guān)系。觀察到三個(gè)帶間躍遷,且能量隨溫度的升高而降低。其中最低能量躍遷的線性溫度系數(shù)隨PbHfO3組分的增加先升高后降低。用變溫橢圓偏振光譜研究不同組分PbHfO3陶瓷的電子能帶結(jié)構(gòu)和介電函數(shù)。參數(shù)ε2max在居里溫度附近有最小值,這是因?yàn)樵谠摐囟认陆Y(jié)構(gòu)發(fā)生變化,從立方(順電)到菱方相(鐵電)的改變。根據(jù)臨界點(diǎn)模型(SCP),從介電函數(shù)的二階導(dǎo)可以得到三個(gè)典型的帶間躍遷能量。躍遷能量對(duì)B位有序度較敏感,隨著溫度的升高呈現(xiàn)紅移趨勢(shì),這與電子與聲子的相互作用和晶格熱膨脹有關(guān)。由于PbHfD3的加入,躍遷能量的線性溫度系數(shù)受氧空位,B位原子(Sc,Ta,Hf)排布和Pb-O鍵的影響而變化。3.采用紅外反射光譜和拉曼光譜研究Pb0.99(Zr0.95Ti0.05)0.98Nb0.0203-x wt.% MgO陶瓷的晶格振動(dòng)在不同溫度下的演變規(guī)律,MgO加入使得高溫鐵電菱方相到低溫相的變化以及有序-無(wú)序轉(zhuǎn)變溫度降低。用遠(yuǎn)紅外反射光譜(5.5-300 K)和拉曼光譜(77-300 K)來(lái)研究分析Mg摻雜的Pb0.99(Zr0.95Ti0.05)0.98Nb0.0203(PZTN)的晶格振動(dòng)和相變。通過(guò)以上互補(bǔ)的實(shí)驗(yàn)手段,在室溫下,所有的陶瓷均是低溫鐵電菱方相[FR(LT)]結(jié)構(gòu)。采用洛倫茲多振子模型得到遠(yuǎn)紅外區(qū)域的介電函數(shù)。與Pb-BO3(B=Zr,Ti,Nb)振動(dòng)相關(guān)的低頻聲子模式主要影響遠(yuǎn)紅外介電響應(yīng)。隨著MgO組分的增加,室溫下的介電函數(shù)ε(0)分別為85.4,73.4,73.9,41.9。這是由Mg替代B位引起的雙重電離氧空位引起的。通過(guò)聲子頻率,阻尼參數(shù)和強(qiáng)度隨溫度的演變規(guī)律,可以觀察到120 K出的有序-無(wú)序相變。該溫度隨著MgO組分的增加略微減小,這與相關(guān)鏈斷裂和局部固有偶極子產(chǎn)生引起的畸變有關(guān)。250 K附近觀察到反鐵電正交相Ao到FR(LT)的相變,這與110方向Pb原子的反鐵電位移和角互連氧八面體的旋轉(zhuǎn)有關(guān)。對(duì)于含MgO的PZTN陶瓷,在290 K附近有從低溫菱方相到高溫鐵電菱方相[FR(HT)]的變化。這個(gè)變化與111方向陽(yáng)離子(Pb和Zr/Ti/Nb/Mg離子)的偏移有關(guān),此溫度比純的PZTN陶瓷的相變溫度略小。
[Abstract]:The ferroelectric oxide is a kind of important functional material information system, is widely used in the field of data storage and photoelectric detection, the Perovskite Ferroelectric Materials, particularly iron bismuth ferrite thin films and ferroelectric antiferromagnetic at room temperature, with good magnetoelectric coupling, high polarization and the photovoltaic effect. In addition, ferroelectric ceramics [PbZZr1-xTixO3 (PZT), PbSc1/2Ta1/2O3 (PST), as a novel functional materials with high dielectric constant, low dielectric loss, piezoelectric and pyroelectric performance, making it high-speed processing in high density information storage, electronic technology and communication, the military field has a wide application prospect. And there is a close relationship between the development of these related functional devices with the characteristics of material system understanding. By adjusting the pulse laser deposition in different growth conditions, changing the substrate, adjust the Zr /Ti component and doping Further study on the physical characteristics of the internal complex such as phase change, phase change is most of the physical mechanism of X ray diffraction characterization of microstructure and dielectric spectrum based on the electronic band structure and electronic transition information is missing. So the research on the physical properties of ferroelectric materials have attracted much attention in the field of information science. Spectroscopy can be used for non destruction detection technology of materials characterization, by spectral analysis, can obtain the optical constants of materials, lattice vibration, electronic energy band structure and electron transition of important information. When the material is in variable temperature conditions, evolution can understand the phonon behavior and interband transition energy during the phase change, phase change material physical mechanism research, development a new and effective way to study physical properties of phase change materials. The main work and innovation points of this paper include the following: 1. study on the pulsed laser deposition method Laser power, oxygen partial pressure and film stress of BiFeO3 thin film lattice vibration, optical transition, frequency effect of.BFO phonon dielectric function with the increase of laser power and increases slightly, the band gap decreases with the decrease of oxygen pressure. The temperature dependent Raman spectra and UV Vis NIR transmission spectroscopy. A1 (TO) phonon frequency and band gap with the increases of temperature. The c axis sapphire substrate BiFeO3 films were prepared at different laser power by pulsed laser method. With the increase of laser power, the lattice constant c/a decreases, Bi/Fe component ratio decreased. At 219172142 cm-1 lateral A1 phonon mode frequency with increasing temperature to lower wavenumber mobile, this is because of thermal expansion, thermal disorder and lattice anharmonicity. In 200500 and 640 K, abnormal low frequency Raman phonon frequency, which correspond to the magnetic phase transition, electric iron sequence The changes between homomorphism and G- type antiferromagnetic phase transition. The laser power caused by the loss of Bi, distortion Bi-O bond length and strength as well as the Fe06 eight face of the local structure, the E (TO) and A1 (TO) increased slightly. The phonon frequency dielectric function in the range of 50-8000cm-1 by Lorenz oscillator model fitting infrared reflectance spectroscopy, transparent dielectric function area changes with the laser power and bulk density, surface roughness and defects. On sapphire substrates at different oxygen partial pressure under the conditions of the preparation of BFO films with the increase of oxygen partial pressure E (TO1), Raman active phonon frequency increased from 74 to 76 cm-1, and the film tensile force on the concentration of.Fe2+ ions and oxygen vacancies increased with decreasing oxygen pressure. The dielectric function obtained by using Tauc-Lorentz dispersion model fitting 0.47-6.5 eV spectra. The absorption edge with increasing temperature (8-300 K) showed red shift Eg. The band gap decreased with the increase of temperature, and the electron phonon effect of distance between atoms in BFO film is related to the interaction. In the 8K, with the decrease of oxygen partial pressure, Eg decreased from 2.88 to 2.78 eV, which is increased by the oxygen vacancy impurity formed between the valence band and conduction band caused by adjust the pressure in the film. The deposition of BFO thin films with different thickness on the substrate of LaAl03 to stress. Films are highly (111) preferred orientation, with the increase of the thickness, the compressive strain decreases, the strain between the film and the bulk crystal ratio were 1.75,1.57 and 1. strain Eg decreased from 2.7 to 2.65 eV and the transition energy increased from 3.5 to 4.1 eV. and the O2p state of the mobile Fe3+ and local crystal field changes related to the charge transfer of.2. (1-x) PST-xPbHfO3 (x = 0 ~ 0.2) dielectric function of relaxor ceramics with temperature change. The relationship between observed three interband transitions, and can The amount decreases with the increase of temperature. The increase of linear temperature coefficient of the lowest energy transition with PbHfO3 component increased first and then decreased. Studied by spectroscopic ellipsometry at different electronic components PbHfO3 ceramic band structure and dielectric function parameters. 2max has a minimum value near the Curie temperature, this is because in the temperature structure changes from cubic to rhombohedral (PE) (ferroelectric) change. According to the critical point model (SCP), from the two order derivative of the dielectric function can be obtained by three typical interband transition energy. The transition energy of the ordered degree of B is sensitive, with the temperature increasing. With this trend, the electron phonon interaction and lattice thermal expansion. Due to the addition of PbHfD3, the linear temperature coefficient of transition energy by oxygen vacancies, B atoms (Sc, Ta, Hf) and Pb-O bond arrangement effect and the changes of.3. by infrared reflectance spectroscopy and Raman Spectra of Pb0.99 (Zr0.95Ti0.05) evolution at different temperatures 0.98Nb0.0203-x wt.% lattice vibration of MgO ceramics, the addition of MgO makes high temperature ferroelectric rhombohedral phase and low temperature to change the order disorder transition temperature decreased. With the far infrared reflection spectra (5.5-300 K) and Raman spectroscopy (77-300 K) to study the Mg doped Pb0.99 (Zr0.95Ti0.05) 0.98Nb0.0203 (PZTN) of the lattice vibration and phase transition. By means of experiment above complementary, at room temperature, all ceramic are low temperature ferroelectric rhombohedral structure. [FR (LT)] by Lorenz oscillator model to obtain the dielectric function of far infrared region. (B=Zr, Ti, and Pb-BO3 Nb) low frequency phonon modes mainly affect the vibration of far infrared dielectric response. With the increase of MgO concentration, the dielectric function epsilon at room temperature (0) were replaced by Mg B 85.4,73.4,73.9,41.9. which is caused by the double ionized oxygen vacancies Cause. The phonon frequency, damping parameters and strength with the evolution of temperature, can be observed that the order disorder phase transition 120 K. The temperature with the increase of MgO concentration slightly decreased, which is associated with the chain fracture and local dipoles caused by the distortion of the.250 K near the observed antiferroelectric orthorhombic phase Ao FR (LT) phase rotation on anti iron electric displacement and angle of interconnection in eight face and 110 oxygen atoms of the Pb direction. For PZTN ceramics containing MgO, around 290 K from low temperature to high temperature rhombohedral ferroelectric rhombohedral [FR (HT)] change. This change with the 111 direction cation (Pb and Zr/Ti/Nb/Mg ions) offset, the temperature of phase transition temperature of PZTN ceramics is smaller than pure.

【學(xué)位授予單位】：華東師范大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2015
【分類號(hào)】：TB34;TQ174.1

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