| 초록 |
BaTiO3 ceramics are one of the most widely used materials in the electronic industry, especially in Multi Layer Ceramic Capacitors (MLCCs), because of their high dielectric constant. The advances in microelectronic packaging and communication technologies necessitate the ultra – high capacity of the MLCC. And in microelectronics and communications have led to the miniaturization and integration of MLCCs in electronic devices. Pushed by the current trend of miniaturization of the devices with improved properties, the nano-sized BaTiO3 particles have attracted considerable attention. As the dielectric material layer of MLCC becomes thinner, the nano-sized BaTiO3 powders, below 70 nm, are more essential to produce the ultra – high capacity of MLCC. It is also important that the nano–sized BaTiO3 powder has higher tetragonality contradictory to size effect. The BaTiO3 nano-sized particles were usually produced by the solid-stae reaction of BaCO3 with TiO2 at high temperature above 900 ℃. However, this method leads to formation of large BaTiO3 nano-sized particles with uncontrolled and irregular morphology. So, the nanoparticles are synthesized via various wet chemical routes such as the oxalate route, a polymetric precursor method, sol–gel process, a micro-emulsion process and the hydrothermal method. In various method for synthesizing BT, the hydrothermal method is especially advantageous to produce nanocrystalline BT particles with superfine particle size, narrow particle size distribution and good crystallinity. Owing to synthesize high crystalline BaTiO3 particles via hydrothermal reaction, high pH (≥ 13) is essential. Generally, KOH, NaOH and ammonia are used to increase the pH. Especially, ammonia has been preferred due to advantage for washing the as-synthesized BaTiO3 particles. Our works focus on the role of ammonia for synthesis of high crystalline BaTiO3 powders via hydrothermal route except increasing the pH. Two kinds of samples were prepared to compare the effects of ammonia. The synthesized BaTiO3 particles are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The TiO2 synthesized by hydrolysis with and without ammonia are analyzed by X-ray photoelectron spectroscopy (XPS). |
