Hyeung-Gyu Lee

Ceramic particle size dependence of dielectric and piezoelectric properties of piezoelectric ceramic-polymer composites

Composites with 0‐3 connectivity were fabricated from barium titanate and phenolic resin powders. These composites were investigated for dielectric and piezoelectric properties with the active particle size. Under the condition of the same density and ceramic/polymer volume ratio, the dielectric constants and piezoelectric coefficients of composite increase as the ceramic particle size in composite increases. The surface layer model was used to explain these phenomena in our composite system and was confirmed experimentally. The thickness and dielectric constant of the surface layer of the powder prepared by grinding the sintered barium titanate ceramics were 1.59 μm and 105. When the ceramic particle size is larger than about 100 μm, the properties of the composite were nearly independent of size.

A study of poly(p-phenylenevinylene) and its derivatives using x-ray photoelectron spectroscopy

Poly(p-phenylenevinylene) and its derivatives (DP-PPV and labeled R-7) were carefully studied using x-ray photoelectron spectroscopy. The C 1s peaks taken from spin-coated thin films of these materials were fitted with the consideration of the bonding state differences (–C=CH and C=C–, etc). The intensity of these C 1s peaks agrees well with the value estimated from the bonding state consideration.

BiFeO3-based Lead-free Piezoelectric Ceramics

Recently, many lead-free piezoelectric materials have been investigated for the replacement of existing Pb-based piezoelectric ceramics because of globally increasing environmental interest. There has been remarkable improvement in piezoelectric properties of some lead-free ceramics such as (Bi,Na)TiO3-(Bi,K)TiO3-BaTiO3, (Na,K)NbO3-LiSbO3, and so on. However, no one still has comparable piezoelectric properties to lead-based materials. Therefore, new lead-free piezoelectric ceramics are required. BiFeO3 has a rhombohedrally distorted perovskite structure at room temperature and a very high Curie temperature (TC= 1,100 K). And a very large electric polarization of 50 ∼ 60 μC/cm 2 has been reported both in epitaxial thin film and single crystal BiFeO3. Therefore, a high piezoelectric effect is expected also in a BiFeO3 ceramics. The recent research activities on BiFeO3 or BiFeO3-based solid solutions are reviewed in this article.

Eco-friendly Ceramic Materials for Shear Mode Piezoelectric Energy Harvesting

Eco-friendly (Na,K)NbO3 (NKN)-based piezoelectric ceramic materials were fabricated by conventional ceramic method for shear mode piezoelectric energy harvesting application. NKN-LiTaO3 (LT) based compositions were adopted for the high d15×g15 which is proportional to harvested energy density. The composition 0.935(Na0.535K0.485)NbO3-0.065LiTaO3 was found to be lie on the boundary of tetragonal and orthorhombic phases. With reducing Ta content, the dielectric constant decreased gradually while maintaining high d15, which resulted in increased d15×g15. The composition 0.935(Na0.535K0.485)NbO3-0.065Li(Nb0.990Ta0.010)O3 was found to possess excellent piezoelectric and electromechanical properties (d15×g15 = 29 pm 2 /N, d15 = 417 pC/N, k15 = 0.55), and high curie temperature (Tc = 455℃).

Low temperature sintering and piezoelectric properties of lead-free (1-x) (Na0.5K0.5)NbO3-xCaTiO3 ceramics

The 0.95NKN-0.05CaTiO3 (0.95NKN-0.05CT) ceramics showed the high piezoelectric properties of d33=241, kp=0.41 and e3T/eo=1316. Therefore, the 0.95NKN-0.05CT ceramic is considered to be a promising candidate for lead-free piezoelectric material. However, its sintering temperature was high and Na2O evaporation occurred. Moreover, Na2O evaporation decreased the specimen resistivity and thus the poling efficiency. Therefore, the sintering temperature of this material needs to be decreased before it gains practical application. Moreover, the decreased sintering temperature is required to allow its application to multilayer devices. In this work, CuO was used to lower the sintering temperature of the 0.95NKN-0.05CT ceramics and variations of microstructure and piezoelectric properties of 0.95NKN-0.05CT ceramics were investigated with CuO addition. The piezoelectric properties of the specimens were considerably influenced by the relative density, grain size and liquid phase amount. The high piezoelectric properties of d33 = 200 pC/N, kp = 0.37, e3T/eo = 1173 and Qm = 350 were obtained for the 0.95NKN-0.05CT ceramics containing 2.0 mol% CuO sintered at 960 oC for 10 h.