本文選題：充滿型鎢青銅 + 弛豫鐵電體��； 參考：《浙江大學(xué)》2015年博士論文

【摘要】：本論文系統(tǒng)地研究了Ba基充滿型鎢青銅鈦鈮酸鹽陶瓷的晶體結(jié)構(gòu)、介電鐵電性能以及相變特征,重點(diǎn)討論了四邊形空隙A1位填充離子對其結(jié)構(gòu)與性能的影響規(guī)律。揭示了鎢青銅結(jié)構(gòu)中弛豫鐵電性產(chǎn)生的結(jié)構(gòu)根源、以及鐵電相變特征隨成分變化的規(guī)律。在Ba5RTi3Nb7O30 (R=La, Nd, Sm)陶瓷中,室溫下均形成了四方鎢青銅結(jié)構(gòu),當(dāng)R=La時(shí)空間群為P4/mbm;而R=Nd和Sm時(shí),空間群為P4bm。Ba5YTi3Nb7O30室溫下形成的四方鎢青銅結(jié)構(gòu)穩(wěn)定性較差。隨著五邊形(A2)與四邊形(A1)填充離子半徑差A(yù)R增大,Ba5RTi3Nb7O30弛豫鐵電相變特征逐漸減弱：Ba5LaTi3Nb7O30為典型的弛豫型鐵電體,介電峰出現(xiàn)的溫度和頻率的關(guān)系符合Vogel-Fulcher公式；而在Ba5NdTi3Nb7O30、Ba5SmTi3Nb7O30的介電溫譜中頻率色散的現(xiàn)象逐漸減弱,同時(shí)介電峰出現(xiàn)的溫度逐漸向高溫方向移動(dòng)。在所有成分中,除了相變溫度附近,低溫處都存在至少一個(gè)介電異常,這與低溫處微區(qū)結(jié)構(gòu)的調(diào)制、尤其是氧八面體的扭曲或變形有關(guān)。在弛豫鐵電體Ba5SmTi3Nb7O30中,當(dāng)一個(gè)Ba離子被Ca替換,其介電溫譜中頻率色散現(xiàn)象將消失,取而代之的是較為尖銳的介電突變峰,表現(xiàn)出正常鐵電體相變的特征。同時(shí),Ba4CaSmTi3Nb7030介電溫譜中相變峰出現(xiàn)的溫度比Ba5SmTi3Nb7O30提高了很多。根據(jù)全譜擬合的結(jié)果,發(fā)現(xiàn)在Ba4CaSmTi3Nb7O30晶胞中,ab平面內(nèi)[Ti/Nb(2)-O(5)]鍵長減小很多,說明小離子Ca2+的填充減少了氧八面體在ab平面內(nèi)的畸變,有利于長程鐵電有序的建立。Ba5SmTi3Nb7O30中,四變形空隙A1無序填充了兩種不同價(jià)態(tài)與半徑的離子,相比于不同電荷形成的微區(qū)電場,晶格中微區(qū)內(nèi)應(yīng)力的不均分布引起周圍氧八面體畸變是弛豫鐵電性更為重要的結(jié)構(gòu)起源。在鎢青銅結(jié)構(gòu)的弛豫鐵電體Ba5RTi3Nb7O30 (R=La、Nd、Sm)中,其低溫電滯回線表明,剩余極化值Pr和最大極化值Pmax均逐漸下降。該現(xiàn)象類似于鈣鈦礦結(jié)構(gòu)的弛豫鐵電體中的“弛豫再入”。其出現(xiàn)的原因可能是由于鎢青銅較為復(fù)雜的結(jié)構(gòu)和離子填充所導(dǎo)致低溫處結(jié)構(gòu)的微擾,進(jìn)而阻礙了極化方向長程鐵電有序的建立。另一方面,隨著溫度降低,鐵電疇翻轉(zhuǎn)形核長大速率降低,微區(qū)結(jié)構(gòu)成分的不均勻在極化翻轉(zhuǎn)過程中起到釘扎的作用,導(dǎo)致低溫處矯頑場逐漸增大,這也是測試過程中出現(xiàn)極化值逐漸下降的一個(gè)重要原因。為了進(jìn)一步研究充滿型鎢青銅結(jié)構(gòu)中A1位四邊形空隙中填充離子對低溫處極化響應(yīng)的影響,制備了Ba5LaxSm1-xTi3Nb7O30 (x=0.1,0.25,0.5,0.8,0.9,0.95)鎢青銅鐵電陶瓷,并表征了其低溫介電弛豫和鐵電特性。隨著La元素的增加,四面體空隙周圍氧八面體晶格畸變增大,導(dǎo)致弛豫鐵電性更為明顯。同時(shí),隨著溫度的降低,極化值下降更為顯著。通過極化值隨著溫度的變化曲線可以發(fā)現(xiàn),有序的離子填充和微觀結(jié)構(gòu)有利于長程鐵電有序的建立,進(jìn)而減弱低溫處“弛豫再入”的特征。Ba4R2Ti4Nb6O30(R= La、Nd、Sm、Eu)陶瓷介電性能及鐵電相變隨A1和A2位離子半徑差的變化規(guī)律與Sr基有類似之處。Ba4La2Ti4Nb6O30為典型的弛豫型鐵電體。而隨著離子半徑差△R增大,Ba4Nd2Ti4Nb6O30, Ba4Sm2Ti4Nb6O30和Ba4Eu2Ti4Nb6O30都表現(xiàn)出正常鐵電體一級相變的特征。而通過Curie-Weiss擬合發(fā)現(xiàn),Ba4Nd2Ti4Nb6O30中T0為100K,而Ba4Sm2Ti4Nb6O30和Ba4Eu2Ti4Nb6O30中T0分別為-522.36K和-317.9K,都為負(fù)值,說明后兩者在相變過程中存在與Ba4Nd2Ti4Nb6O30不同的結(jié)構(gòu)變化。通過電滯回線測試發(fā)現(xiàn),Ba4La2Ti4Nb6O30室溫為順電相,冷卻到193K出現(xiàn)了較小的剩余極化值。Ba4Nd2Ti4Nb6O30高溫時(shí)電滯回線為線性,降溫至393K時(shí)突然出現(xiàn)較大的剩余極化值,符合正常鐵電體相變的特征。然而,Ba4Sm2Ti4Nb6O30和Ba4Eu2Ti4Nb6O30中,高溫在453K附近出現(xiàn)破折狀電滯回線,表現(xiàn)出結(jié)構(gòu)中反鐵電有序的特征。隨著溫度降低,剩余極化值開始出現(xiàn),鐵電相趨于穩(wěn)定而整體表現(xiàn)出亞鐵電性。室溫通過壓電力顯微鏡觀察,發(fā)現(xiàn)微區(qū)出現(xiàn)鐵電疇,證實(shí)其微區(qū)非中心對稱的結(jié)構(gòu)。在Ba5RTi3Nb7O30和Ba4R2Ti4Nb6O30 (R= Nd、Sm)鎢青銅陶瓷變溫拉曼光譜分析表明,當(dāng)測試溫度跨越相變溫度區(qū)間時(shí),對于Ba5RTi3Nb7O30 (R= Nd、Sm)弛豫鐵電體,在低溫處拉曼峰的強(qiáng)度增大同時(shí)部分振動(dòng)模波數(shù)發(fā)生變化,而并未突然消失或出現(xiàn)新的拉曼活性峰,說明弛豫弛豫鐵電體相變過程中結(jié)構(gòu)的逐漸變化。在Ba4R2Ti4Nb6O30 (R= Nd、Sm)中具有正常鐵電體一級相變特征,相變溫度以下發(fā)現(xiàn)低波數(shù)處拉曼振動(dòng)模的分裂,證實(shí)了一級相變中晶體結(jié)構(gòu)的突變與對稱性的降低。
[Abstract]:In this paper, the crystal structure, dielectric ferroelectric properties and phase transition characteristics of Ba based tungsten bronze titanium niobate ceramics are systematically studied. The influence of the quadrangular void A1 bit filled ions on its structure and properties is discussed emphatically. The structural origin of the relaxation ferroelectric production in the structure of tungsten bronze and the characteristics of ferroelectric phase transition are revealed. In Ba5RTi3Nb7O30 (R=La, Nd, Sm) ceramics, the structure of the tetragonal tungsten bronze was formed at room temperature. When R=La, the space group was P4/mbm; while R=Nd and Sm, the space group formed at P4bm.Ba5YTi3Nb7O30 room temperature of the tetragonal tungsten bronze structure was less stable. With the difference between the pentagonal (A2) and the quadrangular (A1) ion radius difference, AR increased. The characteristics of a5RTi3Nb7O30 relaxor ferroelectric phase transition gradually weaken: Ba5LaTi3Nb7O30 is a typical relaxor ferroelectrics, the relationship between the temperature and frequency of the dielectric peaks conforms to the Vogel-Fulcher formula, while the frequency dispersion in the dielectric temperature spectrum of Ba5NdTi3Nb7O30, Ba5SmTi3Nb7O30 decreases gradually, and the temperature of the dielectric peak appears gradually to high temperature. In all components, there is at least one dielectric anomaly at low temperature in addition to the phase transition temperature, which is related to the modulation of the microstructure at low temperature, especially the distortion or deformation of the oxygen eight surface. In the relaxor ferroelectric Ba5SmTi3Nb7O30, when a Ba ion is replaced by Ca, the frequency dispersion in the dielectric temperature spectrum will disappear. At the same time, the temperature of the phase transition peak in the Ba4CaSmTi3Nb7030 dielectric temperature spectrum is much higher than that of Ba5SmTi3Nb7O30. According to the results of the total spectrum fitting, it is found that the [Ti/Nb (2) -O (5)] bond length in the ab plane decreases a lot, indicating that the bond length of the [Ti/Nb (2) -O (5)) decreases a lot. The filling of the ion Ca2+ reduces the distortion in the oxygen eight plane in the ab plane, and is beneficial to the long range ferroelectric order in the establishment of.Ba5SmTi3Nb7O30. The four deformed void A1 is disorderly filled with two different valence and radii ions. Compared to the microelectric field formed by different electric charges, the uneven distribution of the stress in the microsphere in the lattice causes the peripheral oxygen eight surface malformation. In the relaxor ferroelectrics Ba5RTi3Nb7O30 (R=La, Nd, Sm) of the tungsten bronze structure, the low temperature hysteresis loop shows that the residual polarization value Pr and the maximum polarization value Pmax decrease gradually. This phenomenon is similar to the "relaxation reentry" in the relaxor ferroelectrics of the perovskite structure. The reasons for its occurrence may be possible. It is due to the complicated structure and ion filling of tungsten bronze which leads to the perturbation of the structure at low temperature, which hinders the establishment of the ferroelectric order in the polarization direction. On the other hand, with the decrease of the temperature, the rate of the ferroelectric domain turn nucleation growth is reduced and the inhomogeneity of the microstructure component plays the role of pinning in the polarization reversal process. At low temperature, the coercive field increases gradually, which is also an important reason for the gradual decline of polarization in the testing process. In order to further study the influence of the filled ions in the A1 bit space of the full tungsten bronze on the polarization response at low temperature, the Ba5LaxSm1-xTi3Nb7O30 (x=0.1,0.25,0.5,0.8,0.9,0.95) tungsten bronze ferroelectric pottery was prepared. The dielectric relaxation and ferroelectric properties at low temperature are characterized. With the increase of the La element, the lattice distortion of the oxygen eight surfaces around the tetrahedron increases and the relaxation ferroelectric property is more obvious. At the same time, the polarization decreases more significantly with the decrease of the temperature. The microstructure is beneficial to the establishment of long range ferroelectric order, and then weaken the dielectric properties of.Ba4R2Ti4Nb6O30 (R= La, Nd, Sm, Eu) ceramics at low temperature. The variation of the change of the ferroelectric phase transition with the difference of the A1 and A2 bit radius is similar to that of the Sr base..Ba4La2Ti4Nb6O30 is a typical relaxor type ferroelectrics, and with the difference of the ionic radius. With the increase of delta R, Ba4Nd2Ti4Nb6O30, Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30 all show the characteristics of the first order phase transition of normal ferroelectric. The Curie-Weiss fitting shows that T0 in Ba4Nd2Ti4Nb6O30 is 100K, while Ba4Sm2Ti4Nb6O30 and Ba4Eu2Ti4Nb6O30 T0 are -522.36K and negative. D2Ti4Nb6O30 has different structural changes. Through the hysteresis loop test, it is found that the Ba4La2Ti4Nb6O30 room temperature is a paraelectric phase, and the cooling to the 193K has a small residual polarization value.Ba4Nd2Ti4Nb6O30 at high temperature, the hysteresis loop is linear, and when the temperature drops to 393K, a large residual polarization is suddenly appeared, which is the characteristic of the phase transition of the normal ferroelectrics. However, Ba4Sm2Ti4Nb In 6O30 and Ba4Eu2Ti4Nb6O30, there is a broken wire hysteresis loop near 453K, which shows the characteristics of antiferroelectric order in the structure. With the temperature decreasing, the residual polarization begins to appear, the ferroelectric phase tends to be stable and shows the ferroelectric properties as a whole. The central symmetric structure. In the Ba5RTi3Nb7O30 and Ba4R2Ti4Nb6O30 (R= Nd, Sm) tungsten bronze ceramics, the TM Raman spectrum analysis shows that when the test temperature crosses the phase transition temperature range, for Ba5RTi3Nb7O30 (R= Nd, Sm) relaxor ferroelectrics, the intensity of the Raman peaks at low temperature increases and the number of vibrational modes changes, but does not suddenly disappear. The new Raman active peak shows the gradual change in the structure during the phase transition of relaxor ferroelectrics. In Ba4R2Ti4Nb6O30 (R= Nd, Sm), the first order phase transition of normal ferroelectrics is characterized. The splitting of the Raman vibrational modes at low wave numbers is found below the phase transition temperature, which confirms the decrease of the crystal structure in the first order phase transition.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2015
【分類號】：TQ174.1

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