本文選題：負熱膨脹　切入點：鐵電體　出處：《北京科技大學》2017年博士論文　論文類型：學位論文

【摘要】：鐵電體(Ferroelectrie)作為重要的固體功能材料,具有鐵電、壓電、介電和熱釋電等性能,在現(xiàn)代電子工業(yè)中應用廣泛。同時因其晶格具有反常的負熱膨脹性(negative thermal expansion,NTE)而受到關注。從二十世紀初,本課題組重點研究了鈦酸鉛(PbTi03)及其化合物中的NTE,取得了諸多成果,提出了自發(fā)體積鐵電致收縮(spontaneous volume ferroelectrostriction,SVFS)的概念。在對鈦酸鉛基鐵電體的電子結構、晶體結構、自發(fā)極化(Ps)及NTE的大量研究后,認為Pb6s-O 2p雜化作用不僅是晶體結構畸變的關鍵,也是引發(fā)其NTE的核心因素。第一性原理計算表明Pb-O鍵的熱振動對鈦酸鉛的NTE有重要貢獻�；谏鲜鼋Y果,本文進一步研究鐵電體NTE中的基本問題。首先探究了格林艾森定律(Gruneisen relation)在鈦酸鉛NTE中的運用。雖然PbTiO3的主要光學支包括鐵電軟模具有顯著的負格林艾森系數,但并不能描述鈦酸鉛的NTE特征。對PbTiO3軟模的非諧性分析顯示其本征非諧性為重要部分,因此由準諧近似推導的格式定律在此出現(xiàn)異常結果。對比NTE增強的鈦酸鉛基化合物,發(fā)現(xiàn)軟模的本征非諧性與其NTE大小呈正相關。利用氧同位素18O對PbTiO3晶格動力學的改變,仔細研究了熱振動在其NTE中的作用。室溫高分辨同步輻射的衍射分析發(fā)現(xiàn)18O減小了 PbTiO3的晶格常數a,而使沿Ps方向的晶格常數c反常增大(各約萬分之一)。18O對晶格各向異性的改變與PbTiO3的各向異性熱膨脹行為一致。結合變溫Raman和PbL3的EXAFS研究證實了 Pb-O熱振動在極化軸熱收縮中的作用,進一步認識了鈦酸鉛NTE行為的基礎。本文在無鉛鐵電體中確定并研究了硫屬族化合物Sn2P2S6的NTE(243～338 K,一4.7×10-5/K)。結合晶體結構分析與第一性原理計算,由Sn5s-S3p雜化解釋了其NTE過程。Sn2P2S6的Ps相對PbTi03明顯偏弱,但仍具有顯著NTE行為,因此推測這類陰陽離子的s-p雜化作用是鐵電體NTE實現(xiàn)的必要條件。利用同主族的、具備與S3p不同雜化能力的Pb2+/Ge2+進行對Sn2+的替代,以研究其對NTE的調控。最后選取有Sb 5s-S 3p雜化作用的SbSI鐵電體作了進一步驗證,確定了較為明顯的NTE行為(253～293 K,一5.0×10-5/K),支持了上述推測。另外在BaTiO3中的A位引入Ca2+后雖大幅增強了極化軸的熱收縮、削弱約60%的體積熱膨脹系數,但仍未得到可觀的NTE,從側面驗證了 s-p雜化作為鐵電體NTE的必要條件。本文總結得到了具有NTE行為鐵電體的基本特點:s-p雜化和鐵電軟模(位移型相變)。鐵電體的軟模具有顯著的本征非諧性,升高溫度帶來相關原子非諧熱振動的增強,削弱和破壞s-p雜化,導致Ps的減小以及極化軸的劇烈熱收縮,實現(xiàn)單胞體積的NTE。而在不具備上述條件的鐵電體中則很難實現(xiàn)NTE。以上認識給鐵電體NTE的設計和調控提供了重要思路。
[Abstract]:As important solid functional materials, ferroelectrics have ferroelectric, piezoelectric, dielectric and pyroelectric properties. It has been widely used in modern electronics industry and has attracted much attention because of its anomalous negative thermal expansion. From the beginning of 20th century, our group has focused on the study of lead titanate (PbTi03) and its compounds, and has achieved many results. In this paper, the concept of spontaneous bulk ferroelectric shrinkage volume ferro electrostriction (SVFS) is proposed. After a large number of studies on the electronic structure, crystal structure, spontaneous polarization Pss and NTE of lead titanate ferroelectrics, it is concluded that the hybrid action of Pb6s-O 2p is not only the key to the distortion of crystal structure. First principle calculation shows that the thermal vibration of Pb-O bond contributes significantly to the NTE of lead titanate. In this paper, the basic problems in ferroelectrics NTE are further studied. Firstly, the application of Gruneisen relation in lead titanate NTE is investigated. Although the main optical branches of PbTiO3 include the ferroelectric soft mode, it has a significant negative Greeniesen coefficient. But it can not describe the NTE characteristics of lead titanate. The anharmonic analysis of PbTiO3 soft mode shows that the intrinsic anharmonic property is an important part, so the format law derived from quasi harmonic approximation has abnormal results. Compared with the NTE enhanced lead titanate compounds, It is found that the intrinsic anharmonic property of the soft mode is positively correlated with its NTE size. The lattice dynamics of PbTiO3 is changed by using the oxygen isotope 18O. The effect of thermal vibration on NTE is carefully studied. The diffraction analysis of high resolution synchrotron radiation at room temperature shows that 18O decreases the lattice constant a of PbTiO3 and increases the lattice constant c in the direction of Ps (about 1/10000? 18O each). The change of lattice anisotropy is consistent with the anisotropic thermal expansion behavior of PbTiO3. The effect of Pb-O thermal vibration on the thermal shrinkage of the polarized axis is confirmed by combining the EXAFS study with variable temperature Raman and PbL3. The basis of the behavior of lead titanate (NTE) is further understood. In this paper, the NTE(243~338 K, -4.7 脳 10 ~ (-5) / K ~ (-1) of the sulfur compound Sn2P2S6 is determined and studied in lead-free ferroelectrics. The crystal structure analysis is combined with the first-principle calculation. The PS of NTE process. Sn2P2S6 is obviously weaker than that of PbTi03, but it still has significant NTE behavior. Therefore, it is inferred that s-p hybridization of this kind of anion is a necessary condition for the realization of ferroelectric NTE. Pb2 / Ge2 with different heterozygosity from S3p was used to replace Sn2 in order to study its regulation on NTE. Finally, the ferroelectrics of SbSI with Sb5s-S3p hybrid were selected for further verification. The obvious NTE behavior of 253103K, -5.0 脳 10 ~ (-5) / K ~ (-1), supports the above conjecture. In addition, the introduction of Ca2 in the A position in BaTiO3 greatly increases the thermal shrinkage of the polarization axis and weakens the volumetric thermal expansion coefficient of about 60%. The necessary conditions for s-p hybrid as ferroelectric NTE have been verified from the side. In this paper, the basic characteristics of ferroelectrics with NTE behavior:: s-p hybrid and ferroelectric soft mode (displacement-type phase transition) are summarized. Soft modules have remarkable intrinsic anharmonic properties. The increase of temperature leads to the enhancement of anharmonic thermal vibration of related atoms, the weakening and destruction of s-p hybridization, and the decrease of Ps and the sharp thermal contraction of the polarization axis. It is difficult to realize NTE in ferroelectrics without the above conditions. The above understanding provides an important idea for the design and regulation of ferroelectrics NTE.
【學位授予單位】：北京科技大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：TM221

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相關碩士學位論文 前1條

1 韓立仁;Ba_(1-1x)Ca_xTiO_3鐵電陶瓷的制備及結構與性能研究[D];天津師范大學;2012年

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本文編號：1640545