Electrophoretic Deposition Process for BaTiO3/SrTiO3 Functionally Gradient Ceramics

• Main Authors: ChiChang Lin, 林冀昌
• Other Authors: Louh Rong-Fuh
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/82786572780221959423

碩士 === 逢甲大學 === 材料科學學系 === 88 === Electrophoretic deposition (EPD) technique is an effective technique to produce thin or thick ceramic layers onto electrically conductive substrates. The aim of this study is to use the EPD technique to fabricate functionally gradient materials (FGM) for BaTiO3/SrTiO3 ferroelectric layers. The substantial benefits for EPD technique are based on low apparatus cost, ability of layer deposition for complex shape, easy control of layer thickness and its microstructure, and higher deposition rate.Titanate powder of 3.0 g added in 150 ml solvent mixture of acetyl acetone (Acac) and ethanol (EtOH) was formed as an effective EPD suspension. The EPD process parameters consist of volume ratio of organic solvents, suspension concentration, suspension temperature, deposition time, electrical field strength, area of electrode substrate, and different treatments of ceramic powder and EPD suspension. Optimization of EPD process parameters such as the 1:1 volume ratio of Acac and EtOH, suspension temperature of 25oC, applied DC voltage of 100 VDC, electrode distance of 1.0 cm, substrate area of 6.0 cm2, and deposition time of 60 sec were used to obtain (Ba1-xSrx)TiO3 ferroelectric layers with good microstructure quality. Small added amount of acetic acid (CH3COOH) to BaTiO3 EDP suspension to adjust the pH value toward to weak acidity was associated with enhancing deposition efficiency. Ball milling process for both initial ceramic powder and EDP suspension was proved to be beneficial to higher deposition efficiency.Submicron sized PZT powder of 2.0 g added in 150 ml solvent mixture of acetone and toluene was formed as an effective EPD suspension. As for PZT layers by EDP technique, the optimized parameters are consisted of 4:1 volume ratio of acetone and toluene, EDP suspension temperature of 25oC, applied DC voltage of 120 VDC, electrode distance of 1.0 cm, substrate area of 6.0 cm2, and deposition time of 60 sec.Through in-situ adjustment of composition of BaTiO3 and SrTiO3 in EDP suspension, the (Ba1-xSrx)TiO3 ferroelectric layers with FGM-based composite structure were successfully produced by electrophoretic co-deposition (EPCD) route. Various analytic instruments were used to evaluate the quality of microstructural and electrical properties of such BaTiO3 and SrTiO3 ferroelectric layers.The sintered BaTiO3 ferroelectric layers, which were prepared via the EPD route, had sufficiently dense and uniform microstructure. The reduced BaTiO3 powder size by either ball milling for 24 hr resulted in achieving better dielectric properties of deposit layers. To arrange the platinum substrate in horizontal setting in EDP tank, the electrical properties of BaTiO3 layers were ’ = 1800~2500 at 25oC and ’ = 2100~4200 at 120oC for Pt substrate placed at top position and ’ = 1500~2300 at 120oC for Pt substrate placed at bottom position. On other hand, BaTiO3 layers made from EDP suspension with no further ball milling had ’ = 1700~2300 (25oC), 3000~3600 (120oC) and ’ = 1600~2000 (25oC), 2200~3200 (120oC) for platinum substrate placed at top and bottom position, respectively.For FGM-based ferroelectric layers made by means of in-situ adjusting composition in the suspension had ’ = 2000~2500 (25oC), 2800~3500 (120oC) and ’ = 1750~2250 (25oC), 2600~3250 (120oC) for deposition time of 120 sec. and 180 sec., respectively. Furthermore, the ferroelectric FGM specimens were prepared by sequential stacking of individual layer via electrophoretic deposition, drying, and sintering step with alterng BaTiO3/SrTiO3 constituent ratio of 10:0, 8:2, 6;4, 4;6, 2:8, and 0:10. The dielectric properties of above mentioned specimens had ’ = 1400~1500 (25oC), 1265~1680 (120oC) for frequency at 1 kHz, ’ = 500~800 (25oC), 1100~1500 (120oC) for frequency at 10 kHz, and ’ = 300~500 (25oC), 1000~1400 (120oC) for frequency at 100 kHz.