【摘要】：隨著人們對環(huán)境問題關(guān)注度的增加,壓電材料的無鉛化是未來發(fā)展的方向。(K,Na)NbO_3基無鉛壓電陶瓷被認(rèn)為是最有潛力替代傳統(tǒng)鋯鈦酸鉛(PZT)的材料之一,引起了人們的廣泛關(guān)注。本文從壓電材料實(shí)用化的要求出發(fā),圍繞(K,Na)NbO_3基壓電陶瓷的電學(xué)性能及其穩(wěn)定性的表征與增強(qiáng)開展了系統(tǒng)的研究。首先,利用Mn摻雜及極化調(diào)控的方法提高了(K,Na)NbO_3基陶瓷的壓電性能。發(fā)現(xiàn)在(K,Na)NbO_3基陶瓷中摻入適量的MnO2可顯著提高壓電性能,壓電常數(shù)d33由214提高至351 pC/N,增幅達(dá)64%,并深入研究了Mn離子在ABO_3鈣鈦礦結(jié)構(gòu)的占位機(jī)制;同時(shí),通過優(yōu)化極化溫度也可將其壓電性能提高約15%,基于對不同極化溫度下電滯回線的深入分析,提出了一種基于疇翻轉(zhuǎn)與空間電荷聚集競爭的極化理論模型。其次,提出了一種基于壓電常數(shù)-電場d33(E)曲線原位表征壓電常數(shù)溫度穩(wěn)定性的方法。有別于傳統(tǒng)的退火-測試非原位表征途徑,該方法可原位、實(shí)時(shí)地測量壓電常數(shù)隨溫度的變化。采用d33(E)曲線原位研究了Li/Ta/Sb共摻雜(K,Na)NbO_3陶瓷壓電常數(shù)d33的溫度穩(wěn)定性,并發(fā)現(xiàn)隨溫度升高,其d33呈單調(diào)遞減趨勢,至120oC時(shí)降低約40%,這與高溫偏離其多晶型相變區(qū)有關(guān)。為提高(K,Na)NbO_3基陶瓷的溫度穩(wěn)定性,在基體中引入CaZrO_3以減小正交、四方兩相的差異,實(shí)現(xiàn)多晶型相變的平穩(wěn)過渡。結(jié)果表明5%mol CaZr O_3摻雜(K,Na)NbO_3基陶瓷不僅具有很好的壓電性(d33=357pC/N),且其場致應(yīng)變表現(xiàn)出優(yōu)異的溫度穩(wěn)定性,可與商業(yè)化的PZT相媲美。結(jié)合原位變溫變電場同步X射線衍射、壓電力顯微鏡等實(shí)驗(yàn)手段與第一性原理計(jì)算,發(fā)現(xiàn)CaZrO_3摻雜(K,Na)NbO_3基陶瓷良好的溫度穩(wěn)定性來源于場致彌散相變。最后,研究了CaZrO_3摻雜(K,Na)NbO_3基壓電陶瓷的抗疲勞性能,包括單極、雙極及倍半極電場循環(huán)模式。該材料在三種電場循環(huán)模式下,均表現(xiàn)出優(yōu)異的抗疲勞特性。深入研究表明抗單極疲勞性能的提高與疲勞過程中存在軟化效應(yīng)與空間電荷聚集的競爭有關(guān);CaZrO_3的引入可降低陶瓷的c/a比,從而有利于其抗雙極疲勞性能的增強(qiáng);倍半極模式介于單極與雙極之間,因此樣品也表現(xiàn)出很好的抗倍半極疲勞性能。在此基礎(chǔ)上,研究了溫度及電場強(qiáng)度對其單極疲勞特性的影響,揭示溫度較電場強(qiáng)度更加影響(K,Na)NbO_3基陶瓷的單極疲勞性能。
[Abstract]:With the increasing attention to environmental problems, lead-free piezoelectric materials are the future development direction. (Knna) NbO3-based lead-free piezoelectric ceramics are considered as one of the most potential materials to replace the traditional lead zirconate titanate (PZT), which has attracted wide attention. Based on the practical requirements of piezoelectric materials, the electrical properties and their stability of (Knna) NbO3-based piezoelectric ceramics have been systematically studied in this paper. Firstly, the piezoelectric properties of (Knna) NbO3-based ceramics were improved by mn doping and polarization control. It is found that the piezoelectric properties of (Knna) NbO3-based ceramics can be improved by adding a proper amount of MnO2. The piezoelectric constant d33 is increased from 214 to 351pC / N, an increase of 64. The occupation mechanism of mn ions in ABO3 perovskite structure is also studied. By optimizing the polarization temperature, the piezoelectric properties can also be improved by about 15%. Based on the in-depth analysis of the hysteresis loop at different polarization temperatures, a polarization theoretical model based on the competition between domain flipping and space charge aggregation is proposed. Secondly, a method of in-situ characterization of temperature stability of piezoelectric constant based on piezoelectric constant and electric field d 33 (E) curve is proposed. This method can be used to measure the change of piezoelectric constant with temperature in situ, which is different from the traditional non-in-situ method of annealing and testing. The temperature stability of the piezoelectric constant d33 of Li / Ta-Sb co-doped (Knna) NbO3 ceramics was studied by using d33 (E) curve in situ. It was found that the D33 decreased monotonously with increasing temperature, and decreased by about 40% at 120oC, which was related to the deviation of high temperature from its polycrystalline phase transition region. In order to improve the temperature stability of (Knna) NbO _ 3 based ceramics, CaZrO _ 3 was introduced into the matrix to reduce the difference between the orthogonal and tetragonal phases and to realize the smooth transition of the polycrystalline phase transition. The results show that 5%mol CaZr O 3 doped NbO 3 ceramics not only have good piezoelectric properties (d337pC / N), but also show excellent temperature stability in field-induced strain, which can be compared with commercial PZT ceramics. In combination with in-situ thermoelectric field synchronous X-ray diffraction, pressure-power microscopy and first-principle calculation, it is found that the good temperature stability of CaZrO3-doped (Knna) NbO3-based ceramics originates from field-induced dispersion phase transition. Finally, the fatigue resistance of CaZrO3-doped (Knna) NbO _ 3 based piezoelectric ceramics was investigated, including unipolar, bipolar and double hemipolar electric field cycling modes. The material exhibits excellent fatigue resistance under three electric field cycling modes. The further study shows that the improvement of the anti-unipolar fatigue property is related to the softening effect and the competition of space charge accumulation in the fatigue process. The introduction of CaZrO _ 3 can reduce the c / a ratio of the ceramics, which is beneficial to the enhancement of the anti-bipolar fatigue performance of the ceramics. The double haptic mode is between the unipolar and the bipolar, so the sample also shows good fatigue resistance. On this basis, the effects of temperature and electric field strength on the unipolar fatigue properties of (Knna) NbO3-based ceramics were studied. It was revealed that the temperature had more influence on the unipolar fatigue properties of (Knna) NbO3-based ceramics than the electric field strength.
【學(xué)位授予單位】：清華大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2016
【分類號】：TQ174.1

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