本文關(guān)鍵詞：鈮酸鉛基鎢青銅化合物晶體結(jié)構(gòu)與熱膨脹性　出處：《北京科技大學(xué)》2017年博士論文　論文類(lèi)型：學(xué)位論文

  更多相關(guān)文章： 晶體結(jié)構(gòu) 熱膨脹 負(fù)熱膨脹 鎢青銅 非線性光學(xué)

【摘要】：四方鎢青銅結(jié)構(gòu)化合物是除鈣鈦礦結(jié)構(gòu)化合物之外最大的一類(lèi)鐵電體材料,在壓電、介電等領(lǐng)域有著重要的研究?jī)r(jià)值和應(yīng)用前景。四方鎢青銅型鈮酸鉛基化合物由于具有居里溫度高、宏觀極性強(qiáng)等特殊物理性質(zhì)和晶體結(jié)構(gòu)的多樣性而受到關(guān)注,對(duì)其熱膨脹行為的研究和加深對(duì)鎢青銅類(lèi)化合物固體化學(xué)本質(zhì)的認(rèn)識(shí)有助于解決這類(lèi)材料在實(shí)際應(yīng)用當(dāng)中遇到的熱應(yīng)力問(wèn)題。本論文以熱膨脹性為出發(fā)點(diǎn),選擇、設(shè)計(jì)并合成了一系列四方鎢青銅型鈮酸鉛基化合物；系統(tǒng)地研究了(特殊)晶體結(jié)構(gòu)和晶體結(jié)構(gòu)的演變規(guī)律；測(cè)試其熱膨脹性,并揭示了軸向正、負(fù)熱膨脹機(jī)理及與晶體結(jié)構(gòu)、電子結(jié)構(gòu)之間的關(guān)系；設(shè)計(jì)出通過(guò)調(diào)控極性來(lái)調(diào)控?zé)崤蛎浶缘姆椒ā０l(fā)現(xiàn)了具有優(yōu)異非線性光學(xué)性能的非化學(xué)計(jì)量比的四方鎢青銅結(jié)構(gòu)化合物,為極性材料的設(shè)計(jì)提供新思路。首先用變溫X射線衍射方法確定了Pb2KNb5O15具有b方向的軸向負(fù)熱膨脹性。變溫中子衍射精細(xì)結(jié)構(gòu)修正結(jié)果表明鐵電相內(nèi)Pb、Nb原子具有a-b面內(nèi)的極化位移；b方向的負(fù)熱膨脹是由八面體結(jié)構(gòu)之間耦合旋轉(zhuǎn)與畸變直接導(dǎo)致的。第一性原理計(jì)算表明具有6s2孤對(duì)電子的Pb2+與O2-形成Pb-O共價(jià)鍵導(dǎo)致了鐵電極化的增強(qiáng)。Pb2KNb5O15的軸向負(fù)熱膨脹具有框架結(jié)構(gòu)和鐵電熱致收縮兩重特性,而鐵電熱致收縮是其根本原因。通過(guò)引入不同離子,研究了Pb2RNb5O15(R=Na.K0.5Li0.5、K、Rb、Ag)以及Pb3TiNb4O15(PTN)中R離子對(duì)其熱膨脹性的調(diào)控。實(shí)驗(yàn)結(jié)果表明,引入小半徑R離子的化合物傾向于形成a-b面內(nèi)和c方向的規(guī)律性超結(jié)構(gòu),并確定了R=K0.5Li0.5、Ag時(shí)的晶體結(jié)構(gòu)。小半徑R離子能夠有效提高居里溫度并增強(qiáng)鐵電極性,進(jìn)而增強(qiáng)極軸b方向上的負(fù)熱膨脹性；同時(shí),小半徑R離子傾向于引起八面體的傾斜,進(jìn)而使c方向正膨脹加劇。材料的宏觀熱膨脹由這兩個(gè)對(duì)立因素平衡的結(jié)果所決定。采用具有6s2孤對(duì)電子的Bi3+取代(PbR)3+,設(shè)計(jì)并合成新化合物PbBiNb5O15。選區(qū)電子衍射實(shí)驗(yàn)觀察到PbBiNb5O15樣品中高達(dá)五階的非公度調(diào)制衛(wèi)星峰,表明其存在很強(qiáng)的非公度調(diào)制特性。結(jié)構(gòu)解析發(fā)現(xiàn)PbBiNb5O15中A位Pb2+和Bi3+具有大的位置和占位調(diào)制幅度,進(jìn)而形成大的局域偶極矩。PbBiNb5O15通過(guò)非公度的非周期性調(diào)制,使得a-b面內(nèi)的局域偶極矩在長(zhǎng)程上得以抵消,并導(dǎo)致了較弱的宏觀極性。通過(guò)Li的引入得到具有優(yōu)異非線性光學(xué)性能的非化學(xué)計(jì)量比四方鎢青銅化合物Pb2.15Li0.7Nb5O15。結(jié)合中子衍射、X射線衍射精確解析出Pb2.15Li0.7Nb5O15晶體結(jié)構(gòu)并確定了Li占據(jù)四邊形孔洞位置,澄清了Li在鎢青銅中具體位置的爭(zhēng)議。原子級(jí)分辨率透射電鏡成像表明,Pb、Li隨機(jī)分布導(dǎo)致了局域極性增強(qiáng),這可能是優(yōu)異非線性光學(xué)性質(zhì)的原因。
[Abstract]:The tetragonal tungsten bronze compounds are a class of ferroelectric materials except the largest perovskite compound, in piezoelectric, dielectric and other fields have important research value and application prospect. The tetragonal tungsten bronze type niobate lead compounds with high Curie temperature, extremely strong macro diversity and special physical properties of crystals the structure of attention, and to deepen the Study on the thermal expansion behavior of the solid understanding of the chemical nature of tungsten bronze compounds contribute to the solution of this kind of material encountered in the practical application of the thermal stress problem. This paper expands as a starting point, to heat the choice, design and a series of tetragonal tungsten bronze type niobium lead acid based compounds were synthesized; systematically studied (special) evolution of crystal structure and crystal structure; to test its thermal expansion, and reveals the mechanism of axial, and negative thermal expansion and crystal structure, electronic structure The relationship between the structure design; through the regulation of the polarity of the method. The non stoichiometric regulation of heat expansion with excellent nonlinear optical properties than the tetragonal tungsten bronze compounds were found, and provide new ideas for the design of polar material. First determine the axial direction of the B Pb2KNb5O15 with negative thermal expansion with temperature X ray diffraction method. Thermal neutron diffraction results show that the fine structure of modified ferroelectric phase Pb, Nb atoms with A-B in-plane displacement polarization; negative thermal expansion B direction is directly caused by the structure coupling between the eight rotation and distortion. The first principle calculation shows that 6s2 has a lone electron pair Pb2+ and O2- lead the enhanced axial negative thermal expansion of.Pb2KNb5O15 with frame structure and electric iron induced shrinkage characteristics of the ferroelectric polarization Pb-O covalent bond formation, and the electric iron induced shrinkage is the fundamental reason. Through the introduction of different Ion on Pb2RNb5O15 (R=Na.K0.5Li0.5, K, Rb, Ag) and Pb3TiNb4O15 (PTN) R ion on the thermal expansion of regulation. The experimental results show that the regularity of the introduction of small radius of R ions tend to form compounds in A-B plane and c direction of the super structure, and to determine the crystal structure of R= K0.5Li0.5. Ag. The small radius of R ions can effectively improve and enhance the Curie temperature of iron electrode, thus enhancing the negative thermal expansion of b axis direction; at the same time, the small radius of R ions tend to cause eight inclined surface body, and the c direction is inflation intensified. Macro thermal expansion materials determined by the two a factor balanced results. With the 6s2 lone pair electrons of Bi3+ substituted 3+ (PbR), the design and synthesis of new compounds PbBiNb5O15. electron diffraction observed incommensurate modulated satellite peaks in PbBiNb5O15 samples up to five order, show the presence of strong non The incommensurate modulation characteristics. Structure analysis found in PbBiNb5O15 A Pb2+ and Bi3+ with high position and occupying the modulation amplitude, and the formation of local dipole moments.PbBiNb5O15 through non periodic modulation of incommensurate, the local A-B plane dipole moment can be offset in the long term, and lead to the weaker polarity. With the introduction of Li are nonstoichiometric with excellent nonlinear optical properties than the tetragonal tungsten bronze compounds Pb2.15Li0.7Nb5O15. with neutron diffraction, X ray diffraction analytical Pb2.15Li0.7Nb5O15 crystal structure and determine the Li occupied the quadrilateral hole position, to clarify the specific location of the Li tungsten bronze in the dispute. Atomic resolution transmission electron microscopy imaging showed that Pb, Li, random distribution causes local polarity enhancement, which is probably the reason why the excellent nonlinear optical properties.

【學(xué)位授予單位】：北京科技大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類(lèi)號(hào)】：TM221

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本文編號(hào)：1377974