Electrochemical Synthesis and Characterization of Barium Titanate Films

• Main Authors: Chu-Tsun Wu, 伍祖聰
• Other Authors: Fu-Hsing Lu
• Format: Others
• Language: en_US
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/72486703348375578896

博士 === 國立中興大學 === 材料工程學研究所 === 90 === Barium titanate films were synthesized by potentiodynamic and galvanostatic polarization over a wide electrolytic voltage range using 0.5 M Ba(CH3COO)2 and 2 M NaOH as the electrolyte at 55℃. The morphology of the films can be tailored by solely varying the applied electrolytic voltage in the same electrolyte. The BaTiO3 thin films possessed uniformly distributed spherical-like small particles at voltages under 30 V. At voltages above 60 V, crater-shaped and large-grained BaTiO3 thick films were formed. The crater-shaped and large-grained cubic BaTiO3 films were used for further corrosion resistance measurements using 0.1 M NaOH as the corrosive environment. Anodized TiO2 films and pure titanium specimens were also investigated for comparison. The corrosion behavior of the films was studied by means of open-circuit potential measurements and potentiodynamic polarization methods. Open-circuit potential measurements showed that BaTiO3 and TiO2 films existed quite stable corrosion potential of about 0.02 V (vs. Ag/AgCl). This corrosion potential is very close to the open-circuit cathodic potential of oxygen reacting with water. From potentiodynamic polarization results the BaTiO3 films posses better corrosion resistance than TiO2 and pure Ti specimens. The high polarization resistance of BaTiO3 films suggests that the anodic current may be due to the O2 evolution on the exposed Ti surface by transporting OH- ions through open pores of the oxide to react on the titanium surface. Spherical-like BaTiO3 films were also synthesized on heterogeneous substrates such as silicon wafer by combining sputtering and electrochemically anodic oxidation techniques over a wide electrolytic duration from a few seconds to 24 hours. From the J-V curves of anodization, Ti-coated substrates with much smaller grains are electrochemically more active than pure titanium substrates. The substrates have developed much large grains of BaTiO3 film as compared to the tiny grains for pure titanium substrates at the initial stage of growth. The most possible reaction route for the formation on Ti/Si substrates is that BaTiO3 particles nucleate and grow in the liquid phase before depositing onto the substrates. The liquid state reaction would enhance the growth of the particles and then result in the large grain size. For pure titanium substrate BaTiO3 particles nucleate mainly on the surface of titanium oxide precursors. The solid state reaction would then cause a fast nucleation but slow growth, therefore much smaller grain sizes are obtained.