固態反應法製備鈦酸鋇 (Solid State BaTiO3, BT）粉末因其成本優勢與優異的介電特性，近期被大量的使用於電子陶瓷元件中，積層陶瓷電容器 (Multi-layer ceramic capacitor) 是其中之一。藉由不同的起始原料：碳酸鋇與二氧化鈦，觀察其結晶相由低溫至高溫的變化、成核的反應、與其陶瓷體的特性。
為了清楚觀察固態反應初期，鈦酸鋇晶核的形貌，起始原料：2 m2/g 的碳酸鋇與 7 m2/g 的二氧化鈦被使用。所生成 BaTiO3 的目標尺寸為 0.6 μm。600oC 為BaTiO3 (以下簡稱 BT) 與 Ba2TiO4 的起始生成溫度，並可由穿透式電子顯微鏡 (TEM) 之選區繞射，確認中間相Ba2TiO4的存在，從該溫度開始，碳酸鋇與二氧化鈦快速的消耗，並開始鈦酸鋇的成核，隨著溫度升高，立方晶鈦酸鋇晶核 (Cubic BT nuclei) 不斷成長，而成為單一顆粒，煆燒溫度再升高，則正方晶鈦酸鋇 (Tetragonal BT) 可獲得。藉由較粗的起始原料可清楚觀察到在低溫時 BT 的生成與結晶相的轉變。藉由修飾粉末 (dopant) 的添加，獲得了具X7R特性的介電陶瓷體。
為研究不同起始粒徑的碳酸鋇與二氧化鈦其生成BT的活化能差異與晶核形貌，使用起始原料：BaCO3 (比表面積10 and 30 m2/g) 與 TiO2 (比表面積7 m2/g)，其所生成 BaTiO3 的目標尺寸為 0.4 μm。其中較細的碳酸鋇 (30 m2/g) 混合物於 1000oC的煆燒下，固態反應提前，所需的活化能較低且可獲得 c/a > 1.010，均勻，粒徑分布較狹窄且平均粒徑為 350nm 之 BT，其陶瓷體特性滿足 X7R，甚至有機會滿足 X8R 電容溫度特性的要求，並在掃描穿透式電子顯微鏡的元素分析下(STEM-EDS)，呈現清楚的核-殼 (Core-Shell) 結構，而修飾粉中的稀土元素，釔（Y），則分布於殼 (shell) 與 晶界 (grain boundary)。
最後，為了製備 < 0.2 μm 的正方晶系鈦酸鋇，極細的碳酸鋇與二氧化鈦為起始原料：BaCO3 (比表面積30 m2/g) 與TiO2 (比表面積190 m2/g)，觀察BT於不同煆燒溫度之相生成。利用 TEM 發現起始原料間的表面擴散於400oC發生，熱重分析 (DTG) 可看出所有的失重反應於600oC以前即完成；使用X-ray 繞射(XRD)偵測500oC的樣品可確定BT 的生成；為此，推論在此起始原料混合系統中，表面擴散與晶格擴散 (bulk lattice diffusion) 應幾乎於同一時期完成，為此，DTG 以單一peak (600oC) 呈現。在煆燒溫度於900oC 與 1000oC，150 nm 以及 250 nm的正方晶 BT (c/a ratio > 1.006) 可從起始原料：比表面積30 m2/g 的BaCO3 與比表面積190 m2/g 的TiO2 分別獲得。其陶瓷體滿足 X7R 電容溫度特性的要求。在STEM-EDS的觀察下，呈現清楚的 Core-Shell 結構，而修飾粉中的稀土元素，Y，則分布於殼 (shell) 與 晶界 (grain boundary)。Core-Shell 結構存在於1000oC-250 nm與900oC-150 nm正方晶相鈦酸鋇的樣品中。

The solid-state synthesis, phase evolution, and nucleus growth of the barium titanate (BaTiO3, BT) powder were investigated in this study. Rapid nucleus growth and precursor phase formation of BT were observed at a relatively low temperature of 600oC by mixing BaCO3 (2 m2/g) and TiO2 (7 m2/g) with a high-energy bead mill. The decomposition of BaCO3 and the formation of the Ba2TiO4 phase were identified by transmission electron microscopy (TEM). On the basis of this observation, the weight loss observed at 600oC in the derivative thermogravimetry (DTG) curve could also be explained. Furthermore, with increasing calcination temperature, single cubic BT with less than 80 nm fine nuclei/crystallites was observed at 900oC, and tetragonal BT (c/a > 1.008) with an average particle size of 0.4 μm was obtained at 1000oC. With regard to the dielectric properties of sintered ceramics, the relative permittivity (εr) increased with calcination temperature, and the Curie point also shifted to a progressively higher temperature. However, BT nucleus samples (with low calcination temperatures of 800 and 900oC) could not satisfy the X7R requirement (Electric Industries Association Standard, the tolerance of capacitance from –55 to +125oC is ± 15 %) until calcination temperature increased to 1000oC.
Two different specific surface area of starting BaCO3: 10 and 30 m2/g, are also used to prepare solid-state BaTiO3 powder. DTG and two kinetic models: Kissinger’s and Reich’s relation, are used to study the solid-state reaction of BT. Pure tetragonal BT was obtained at a lower calcination temperature with BaCO3 of higher specific surface area (SSA). The calculation of activation energy (Ea) also agreed with the result that BaCO3 with higher SSA may speed the BT formation and growth. A clear, thin BT layer and nano-sized cubic BT clusters were observed at calcination temperatures of 600 and 700oC. A narrower particle size distribution and pure tetragonal BT with an average particle size of 350 nm were obtained from 30 m2/g of starting BaCO3 at 1000oC. After sintering with reducing atmosphere, the ceramics with potential of X8R or X7R specifications and a clear core/shell microstructure were obtained in this study.
The phase evolution, nucleation and sintered ceramics of barium titanate powder prepared by solid-state synthesis with an ultra-fine starting material (30 m2/g of BaCO3 and 190 m2/g of TiO2) were investigated. Surface diffusion between BaCO3 and TiO2 was observed at a relatively low temperature of 400oC by transmission electron microscopy (TEM). Rapid nucleation of the BT and cubic BT phases was observed at 500oC by X-ray diffraction (XRD). The derivative thermogravimetry curve clearly shows a single step of BaTiO3 formation at 600oC. In short, pure BT particles with an average particle size of 250nm and high tetragonality were prepared by solid-state synthesis, which produced X7R ceramics with high dielectric permittivity, high resistivity, and a clear core-shell structure.

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