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  4. Synthesis of Nb nano-coating and characterization of coated BaTiO3
 
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Synthesis of Nb nano-coating and characterization of coated BaTiO3

Date Issued
2007
Date
2007
Author(s)
Kan, Chia Chia
DOI
en-US
URI
http://ntur.lib.ntu.edu.tw//handle/246246/55367
Abstract
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.
Subjects
鈮
鈦酸鋇
奈米鍍膜
殼-核結構
電性
Nb
BaTiO3
coating
core-shell
dielectric properties
Type
thesis
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