Synthesis of Nb nano-coating and characterization of coated BaTiO3
Kan, Chia Chia
|Keywords:||鈮;鈦酸鋇;奈米鍍膜;殼-核結構;電性;Nb;BaTiO3;coating;core-shell;dielectric properties||Issue Date:||2007||Abstract:||
本研究揭示一種鈮化物在鹼性環境下於鈦酸鋇粉體表面產生均勻奈米層狀鍍層的方法。本研究利用氯化鈮水溶液在鹼性下會產生回溶現象，並將分散良好之鈦酸鋇鹼性漿料加入作為基底粒子，經由酸液滴定及持續的混合攪拌後，可增加水溶液中鈮離子的反應量，並在鈦酸鋇粒子表面形成厚度小於50奈米的層狀鍍膜。此外，經由感應耦合電漿發射光譜分析儀(ICP-OES)分析發現，鋇離子的溶出問題在整個鍍膜過程可完全被抑制。利用ICP-OES分析鈮離子在不同pH下之殘留結果發現，鈮離子在無添加鈦酸鋇粒子存在時，當pH<11時溶解度明顯下降，而析出物經X光繞射儀(XRD)分析為鈮酸物(niobium acid, HNbO3)。經奈米鍍膜後之鈦酸鋇粉體則添加二氧化矽(SiO2)和三氧化二錳(Mn2O3)於粉體中進行燒結，其分別作為助燒結劑以及在還原氣氛燒結中之電性補償添加劑。燒結方面，主要探討不同鈮添加量對燒結行為的影響，以及生成之二次相和殼-核結構的觀察。這部份利用熱機械性質分析儀 (TMA)，XRD，掃描式電子顯微鏡(SEM-EDX)和穿透式電子顯微鏡附設能量分散光譜儀(TEM-EDX)進行分析和觀察。最後，比較本研究所製備之樣品及傳統固態混合法所得之樣品的介電性表現，包括﹕介電值(K)，絕緣電組(IR)，介電損失(tan
Different from conventional solid-state mixing, this study discovered a method of homogeneous coating process for niobium (Nb) on BT powders. The nano-coating process was implemented in the alkaline condition of using niobium chloride (NbCl5) being the precursor solution. The precipitation behavior of Nb without and with the presence of BT particles, as a function of pH was quantitatively determined by inductance coupled plasma (ICP-OES). The amphibious solubility property of Nb5+ in aqueous solution was found and showed a poor solubility about pH < 11 without the addition of BT particles. The crystalline phase of the precipitation of Nb is determined to be niobium acid (HNbO3) by X-ray diffractometry (XRD). By titrating the mixture of Nb-solution and BT suspension from pH = 11.5 to pH = 11.2, a homogeneous layer coating with a thickness less than 50 nm can be obtained. Besides, the leaching of Ba2+ could be completely suppressed in the coating process.
In addition, the Nb-BT powders were prepared from nano-coating and conventional solid-state mixing for comparison. SiO2 and Mn2O3 powders were added as sintering aid and charge compensator to the Nb-BT powders, respectively. The sintering treatment was carried out at 1225oC for 1 h under reducing atmosphere (1% H2-99% N2) and then annealing at 1000oC for 1h in pure N2 through water at RT. The microstructure features of the sintered ceramics were investigated by SEM-EDX (scanning electron microscope equipped with energy dispersive spectroscopy) and XRD. The formation of “core-shell” structure with Nb concentration gradient was observed by transmission electron microscope (TEM-EDX) and dielectric properties were measured by AC impedance analyzer. The dielectric constant (K) of nano-coating and solid-state mixing specimens show average values ~2000. Apart from solid-state mixing, nano-coating specimens have more stable TCC (temperature coefficient of capacitance) and satisfy the requirement of X7R (EIA) which confirms the more uniform distribution of Nb content in the nano-coating process.
|Appears in Collections:||材料科學與工程學系|
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