傳統製備PTO以及PZT粉末最普遍的方法是採用固態法。然而,採取此法通常會造成燒結性質及均勻性不佳、成分比例偏離、以及粒徑較大的問題，故此製程並不適用於尖端產業之應用。而化學製程,特別是溶凝膠法 (Sol-Gel Process),比起固態法製程提供更多的優點，因而引起我們高度的興趣。在溶凝膠法中最重要的關鍵乃是將所有物系予以溶解使之形成溶液態，因此以分子級的程度達到混合是可能的，且若此種程度之混合持續維持到水解後轉變成gel，進而最終轉變為金屬氧化物，則我們可得到相當均勻之產物。
在本論文中，我們將探討以溶凝膠法在低溫下合成PTO 以及PZT奈米粉末並觀測其低溫及高溫下之晶相。另外，我們也觀察在calcination過程中，對於不同酸鹼度水解條件下所水解製備之粉末其燒結及晶粒成長的現象。
在製備lead titanate的部分，首先我們先藉由將烷氧鈦及醋酸鉛相互混合再予以迴流72小時來合成我們所需之前驅物。因此我們可以利用溶凝膠法將此前驅物水解而在低溫(約150°C)得到Pb2Ti2O6 (major) 以及 PbTi3O7 (minor)粉末。 另外，我們發現水解時的pH值差異並不會影響低溫下的結晶性。 在此低溫下得到的晶粒大約為 2-5 nm。 將乾燥完的粉末繼續加熱， Pb2Ti2O6 與 PbTi3O7 這兩相將在約400-450°C 時轉變成PbTiO3 晶相， 並有微量的未轉換之 PbTi3O7 共存。 當水解條件是在酸性下進行時，我們可以在約600°C下得到純的tetragonal 晶系的 PbTiO3 ，然而在中性下水解,溫度要達到700 °C 才可以得到純的tetragonal 晶系的 PbTiO3。 除此之外， 我們更進一步探討奈米級的PbTiO3 粉末之燒結及晶粒成長現象， 我們發現在酸性水解所得到的粉末可以在較低溫下展現出其優良的燒結現象。

另外，PZT固溶體，Pb(Zr1-xTix)O3 ，具有實用的鐵電及壓電性質，尤其在成分為x=0.45-0.5的比例之下(MPB)展現其優異的壓電效應，使它在近年來更是引起我們的注意。因而我們試著將相同水解條件套用在PZT的製備上來觀察與比較PZT 和 PTO 兩者前驅物水解後結晶行為上之異同。除此之外，我們也觀察在calcination過程中，對於不同酸鹼度水解條件下所水解製備之粉末其燒結及晶粒成長的現象。

在在第三章中製備PZT部分，首先我們先藉由將烷氧鈦、烷氧鋯及醋酸鉛相互混合再予以迴流72小時來合成我們所需之前驅物。再利用溶凝膠法，在pH=3酸性水解的條件下，我們在低溫下(約150°C)可以得到純的tetragonal 晶系的 PZT， 而無任何的pyrochlore 相生成。 持續再將這些粉末加熱，則 tetragonal perovskite PZT 相的結晶性將更強。反之，在中性及鹼性下進行水解，在低溫下得到的粉末其為非晶態，再持續將這些粉末加熱，則非晶態的粉末將在 500-600°C 下轉換成pyrochlore相與tetragonal perovskite PZT 相兩相存， 再繼續加熱到600-700°C時，則pyrochlore相會完全轉換成tetragonal perovskite PZT 相。另外，我們也探討這些奈米級PZT粉末的燒結性質。在酸性及鹼性水解所得到的粉末，其在低溫下可以觀察到良好的燒結現象。

Traditionally, the most common method for preparing PTO and PZT powders was solid state reaction. This kind of reaction is to react a mixture of metal oxides, hydroxides or salts in the solid state. However, this method resulted in poor sintering behavior, a lack of homogeneity, large aggregates formation and poor control of cation stoichiometry; hence, this method was inadequate for various advanced applications. Chemical routes, particularly sol-gel process, offer advantages over the solid state reaction and have attracted strong interest. The most important step in sol-gel process is to obtain a solution of all target components in the form of soluble compounds, so mixing at the molecular level made possible, and if this level of mixing can be retained in the subsequent conversion to gel, and ultimately to oxides, a very homogeneous product results.

In this thesis, we investigated the sol gel process to prepare the PTO and PZT nanocrystalline powders at low temperature, and also examined the crystal phase at the as-prepared state and higher temperatures. Moreover, we observed and compared the sintering and grain growth behavior upon calcination at higher temperatures for different pH values in the hydrolysis step.

In the preparation of lead titanate, first we synthesized the precursor by mixing titanium isopropoxide and lead acetate in ethanol and then refluxed this mixture for 72 hours. Consequently, we could obtain nanocrystalline Pb2Ti2O6 (major) and PbTi3O7 (minor) at low temperature (150°C) by hydrolysising this precursor and dried. As a result, the pH values in the hydrolysis step did not influence the crystallinity of the powders at low temperature. The grains obtained at this low temperature had the size ranging around 2-5 nm. While further heating the as-prepared powders, the phases Pb2Ti2O6 and PbTi3O7 gradually transformed to PbTiO3 at roughly 400-450°C with some extent of PbTi3O7 remained untransformed. The temperature obtaining pure tetragonal perovskite PbTiO3 phase was lower in the powders hydrolysis in acid condition, which is around 600°C, compared with that in neutral condition (700 °C). Furthermore, we investigated the sintering and grain growth behavior of these nanocrystalline PbTiO3 powders at higher temperatures. Enhanced sinterability also could be observed at lower temperature for the powders hydrolysis in acid condition.

Moreover, since the solid solution system Pb(Zr1-xTix)O3 ,PZT, exhibited useful ferroelectric and piezoelectric properties. In particular, compositions near the morphotropic phase boundary (MPB) around x=0.45– 0.5 have attracted considerable interest for many years due to their high piezoelectric response. Thus we further used the same reaction condition to hydrolysis PZT precursor to examine the results between the powders hydrolysising from these two precursors. Besides the investigation of crystallinity at low temperature, we also study the sintering behavior and phase transformation pathway for these two nanosized materials.

In the preparation of PZT, first we synthesized the precursor by mixing titanium isopropoxide, zirconium butoxide and lead acetate in ethanol and then refluxed this mixture for 72 hours. Consequently, we could obtain white powders by hydrolysising this precursor and dried. As a result, we could obtain tetragonal perovskite PZT phase directly, without any pyrochlore phase formation, at low temperature (as-prepared state, 150°C) by sol gel process only when the hydrolysis condition was kept in acid condition (pH=3). Upon calcining the powders, the tetragonal perovskite PZT phase crystallinity was much stronger at higher temperatures.

Whereas, in the neutral and basic conditions, the powders obtained at low temperature revealed the amorphous nature, and further calcining these amorphous powders, the amorphous powders were gradually transformed to pyrochlore and tetragonal perovskite PZT phase at 500-600°C, and the pyrochlore phase was eventually transformed to tetragonal perovskite PZT phase at 600-700°C. Furthermore, we investigated the sintering and grain growth behavior of these nanocrystalline lead zirconate titanate powders. Enhanced sinterability also could be observed at lower temperature for the powders hydrolysis both in acid and basic conditions.

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