本文選題：無鉛鐵電陶瓷 + 電熱效應(yīng)　； 參考：《南京大學(xué)》2015年碩士論文

【摘要】：研究低功耗、高能效且環(huán)境友好的新型制冷技術(shù),替代傳統(tǒng)的壓縮制冷,已經(jīng)成為人們生產(chǎn)生活的迫切需要。在各種各樣的替代型制冷技術(shù)中,電熱制冷備受關(guān)注。它利用鐵電材料的電熱效應(yīng)進(jìn)行制冷,具有低成本、高能量轉(zhuǎn)換率等優(yōu)勢。事實上在電熱材料研究進(jìn)程中,鉛基化合物的電熱性能普遍高于無鉛材料,然而日益嚴(yán)苛的環(huán)保政策制約著含鉛材料的商業(yè)化應(yīng)用,因此提高無鉛材料的電熱性能已經(jīng)成為必然趨勢。其中,尋找在室溫附近具有大電熱效應(yīng)和寬工作溫區(qū)的無鉛鐵電材料就是研究熱點之一。鈦酸鋇是目前無鉛電熱性能研究領(lǐng)域中的重要基體材料,通過離子取代和摻雜改性等方法可以提升材料的電熱性能。其中,BaSnxTi1-xO3(簡稱BST)體系陶瓷具有優(yōu)異的介電、鐵電、熱釋電等性能,存在多相交界點和準(zhǔn)同型相界,且該體系的鐵電相變溫度接近室溫,是潛在的高性能電熱制冷材料。本文系統(tǒng)研究了BST體系陶瓷的成分、介電鐵電性能、微觀結(jié)構(gòu)與電熱性能之間的關(guān)系,提出增強無鉛陶瓷材料在室溫下的電熱效應(yīng)的方法。本研究工作采用固相法制備了BaSnxTi1-xO3 (x=0.02,0.06,0.08,0.10,0.12,0.15,0.18)7個組分的陶瓷樣品。利用XRD、SEM進(jìn)行微觀結(jié)構(gòu)分析,發(fā)現(xiàn)Sn4+對晶粒生長有抑制作用。BST體系的介電溫譜研究表明,隨著錫含量的增加,陶瓷鐵電-順電相變的彌散程度逐漸明顯。室溫下的電滯回線體現(xiàn)了多相臨界點和準(zhǔn)同型相界對材料鐵電性能的增強作用。通過測試各組分陶瓷的變溫電滯回線,然后基于麥克斯韋方程間接推導(dǎo)其電熱性能,并分析BST各組分陶瓷的電熱性能與鐵電相變之間的關(guān)系。根據(jù)BST各組分陶瓷電熱性能的對比分析,我們得出以下結(jié)論：(一)四相臨界點處由于多相共存,擁有數(shù)目較多且能量接近的極化態(tài),在電場變化時容易引起較大的熵變,從而導(dǎo)致大的電熱效應(yīng)。另外由于此處各極化態(tài)之間轉(zhuǎn)變的能量較小,所以在較低的電場下即可引起大電熱效應(yīng)。BST陶瓷體系在準(zhǔn)四相臨界點附近組分(x=0.12)體現(xiàn)出最優(yōu)益的電熱性能,在10kV/cm時,電熱強度為△T/△E=0.027 Kcm/kV和△S/△E=0.0345 Jcmkg-1K-1kV-1。(二)鐵電彌散相變會拓寬陶瓷的電熱制冷溫度區(qū)間。與純鈦酸鋇的狹窄電熱峰不同,由于存在鐵電彌散相變,BST(x=0.12)在接近室溫的較寬溫區(qū)(Tspan=55K)中維持高電熱效應(yīng)。而居里溫度更低的x=0.18的電熱半峰寬更是擴大到70 K,表明其在室溫范圍內(nèi)具有穩(wěn)定的電熱性能。(三)準(zhǔn)同型相界(MPB)可以提高陶瓷在室溫附近的電熱效應(yīng)。BST陶瓷x=0.02在MPB附近的電熱強度(△T/△E)高達(dá)0.037 Kcm/kV。另外當(dāng)F-F相變與F-P相變溫度接近時,電熱效應(yīng)的銜接有助于拓寬電熱材料的工作溫區(qū)。這使得x=0.08在接近100 K的溫區(qū)中都有較為出色的制冷溫度和熵變輸出。
[Abstract]:It has become an urgent need for people to study new refrigeration technology with low power consumption, high energy efficiency and environmental friendliness, instead of traditional compression refrigeration. Among all kinds of alternative refrigeration technologies, electrothermal refrigeration has attracted much attention. It uses the electrothermal effect of ferroelectric materials for refrigeration, which has the advantages of low cost and high energy conversion rate. In fact, in the research process of electrothermal materials, the electrothermal properties of lead-based compounds are generally higher than those of lead-free materials. However, increasingly stringent environmental policies restrict the commercial application of lead-based materials. Therefore, it has become an inevitable trend to improve the electrothermal properties of lead-free materials. Among them, finding lead-free ferroelectric materials with large electrothermal effect and wide working temperature range near room temperature is one of the research hotspots. Barium titanate is an important substrate material in the field of lead-free electrothermal properties. The electrothermal properties of the materials can be improved by ion substitution and doping modification. The ceramics of BaSnxTi1-xO3 (abbreviated as BST) have excellent dielectric, ferroelectric and pyroelectric properties, and there are multiphase junction points and quasi-homogeneous phase boundaries. The ferroelectric phase transition temperature of the system is close to room temperature, so it is a potential high performance electrothermal refrigeration material. In this paper, the relationship among the composition, dielectric ferroelectric properties, microstructure and electrothermal properties of BST ceramics has been systematically studied, and a method to enhance the electrothermal effect of lead-free ceramics at room temperature has been proposed. In this study, the ceramic samples of 7 components of BaSnxTi1-xO3 were prepared by solid state method. The samples were 0.06%, 0.08%, 0.10, 0.12, 0.15, 0.18). The dielectric temperature spectra of Sn4 system show that the dispersion of ferroelectric-paraelectric phase transition becomes more and more obvious with the increase of tin content. The hysteretic loop at room temperature reflects the enhancement of ferroelectric properties by multiphase critical point and quasi-homogeneous phase boundary. By testing the hysteresis loop of each component ceramics, the electrothermal properties of each component ceramics are deduced indirectly based on Maxwell equation, and the relationship between the electrothermal properties and ferroelectric phase transition of BST ceramics is analyzed. Based on the comparative analysis of the electrothermal properties of BST ceramics, we draw the following conclusions: due to the coexistence of multiphase, there are many polarized states with close energy at the critical point of four phases, which can easily cause large entropy change when the electric field changes. This results in a large electrothermal effect. In addition, because the energy of the transition between the polarization states here is small, the large electrothermal effect can be induced at a lower electric field. BST ceramic system shows the optimum electrothermal performance near the quasi four-phase critical point. At 10kV/cm, The electrothermal strength is T / E 0.027 Kcm/kV and S / E 0. 0345 Jcmkg-1K-1kV-1. (2) Ferroelectric dispersion phase transition will widen the temperature range of electrothermal refrigeration of ceramics. Different from the narrow electrothermal peak of pure barium titanate, the high electrothermal effect is maintained in a wide temperature range near room temperature due to the existence of ferroelectric dispersion phase transition (BST) 0.12). The electrothermal half-width of x _ 2O _ 0.18 with lower Curie temperature is increased to 70K, which indicates that it has stable electrothermal performance at room temperature. (3) the quasi-homogenous phase boundary (MPB) can increase the electrothermal effect near room temperature. The electrothermal strength (T / E) of BST ceramics near MPB is as high as 0.037 Kcm / KV. In addition, when the temperature of F-F phase transition and F-P phase transition is close to that of F-P phase transition, the convergence of electrothermal effect is helpful to widen the working temperature range of electrothermal materials. This results in the excellent cooling temperature and entropy output in the temperature range of nearly 100 K.
【學(xué)位授予單位】：南京大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TQ174.7

【共引文獻(xiàn)】

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