Hyun-Ji Noh

Dielectric and Pyroelectric Properties of Dy-doped BSCT Thick Films by Screen-printing Method

(Ba 0.57 Sr 0.33 Ca 0.10 )TiO₃ (=BSCT) powders, prepared by the sol-gel method, were doped using MnCO₃ as the acceptor and Dy₂O₃ as the donor. This powder was mixed with an organic vehicle. BSCT thick films were fabricated by the screen-printing techniques on the alumina substrate. The structural and dielectric properties of BSCT thick films were investigated with variation of the Dy₂O₃ amount. As a result of the differential thermal analysis (DTA), the exothermic peak was observed at around 670℃ due to the formation of the polycrystalline perovskite phase. All the BSCT thick films showed the XRD patterns of a typical polycrystalline perovskite structure. The average grain size of BSCT thick films decreased with an increasing amount of Dy₂O₃. The relative dielectric constant and dielectric loss of the BSCT thick film doped Dy₂O₃ 0.1㏖% were 4637.4 and 1.6% at 1㎑, respectively.

Effect of Sintering Temperature on Structural and Dielectric Properties of (Ba 0.54 Sr 0.36 Ca 0.10 )TiO 3 Thick Films

Barium strontium calcium titanate powders were prepared with the sol-gel method. Ferroelectric (BSCT) thick films were fabricated by the screen-printing method on alumina substrate. Then we investigated the structural and dielectric properties of the BSCT thick films at different sintering temperatures. The thermal analysis showed that the BSCT polycrystalline perovskite phase formed at around . The X-ray diffraction analysis showed a cubic perovskite structure with no second phase present in all of the BSCT thick films. The average grain size and the thickness of the specimens sintered at were about and , respectively. The relative dielectric constant increased and the dielectric loss decreased as the sintering temperature was increased; for BSCT thick films sintered at the values of the dielectric constant and the dielectric loss were 5641 and 0.4%, respectively, at 1 kHz.

ELECTRICAL AND MECHANICAL CHARACTERISTICS OF EPOXY-NANOCLAY COMPOSITE

In this study, we investigated the effects of nanoclay additives on the electrical and mechanical properties of diglycidyl ether of bisphenol A (DGEBA) epoxy resin. Epoxy-clay nanocomposites were synthesized using organically modified two montmorillonite clays (MMT) with different interlamellar spacing (31.5 A and 18.5 A). The electrical and mechanical properties of epoxy-clay nanocopomosites were measured with variation of the amount and type of clay. The nanocomposites were found to be homogenous materials although the nanocomposites still have clay aggregates with increasing nanoclay contents. The dielectric constant showed between 3.2 ~ 3.5 and the dielectric loss showed between 3.2 ~ 5.7% in all nanocoposites. The dielectric strength and tensile strength of the 5 wt% Cloisite 15A added epoxy-oclay nanocomposite were 23.9 kV/mm and 86.7 MPa, respectively.

Characteristics of Lanthanum Silicates Electrolyte for Solid Oxide Fuel Cells

La9.33(Si5V1)O26 ceramics were fabricated by the mixed oxide method for solid oxide electrolytes. La9.33(Si5V1)O26 specimens showed the hexagonal, space group P63 or P63/m, and the unit cell volume increased when the sintering temperature increased. The specimen sintered at 1,400℃ showed the X-ray patterns of the homogeneous apatite single phase without the second phase, such as La2SiO5 and SiO2. The specimen sintered at 1,400℃ showed the maximum sintered density of 4.93 g/cm3. When the sintering temperature increased, the electrical conductivities increased, the activation energy decreased and the values were 7.83×10−4 S/cm, 1.61 eV at 600℃, respectively.

ELECTRICAL PROPERTIES OF HETEROLAYERED BaTiO3/(Bi1/2Na1/2)TiO3 THICK FILMS

The heterolayered BT/BNT thick films were fabricated by screen printing techniques on alumina substrates electrodes with Pt. Their structure and ferroelectric properties were investigated with the heterolayered tetragonal/rhombohedral structure composed of the BT and the BNT thick films. The structural and electrical properties of the heterolayered BT/BNT thick films were studied. The dielectric properties such as dielectric constant, loss and remanent polarization of the heterolayered BT/BNT thick films were superior to those of single composition BNT, and those values for the heterolayered BT/BNT thick films were 1455, 0.025 and 12.63 µC/cm2.

Densification And Ferroelectric Properties Of Pzt(60/40) Thick Films Fabricated By Screen-Printing Method

Ferroelectric PbZr0.6Ti0.4O3 (PZT) thick films were fabricated using a combination of screen-printing method and PZT precursor sol coating process (M. Koch, N. Harris, R. Maas, A. G. R. Evans, N. M. White and A. Brunnschweiler, Meas. Sci. Technol. 8 (1997) 49; Y. S. Yoon, J. Korean. Phys. Soc. 47 (2005) 321). Structural and electrical properties of the PZT thick films with the treatment of sol coating were investigated. The porosity decreased and the densification was enhanced with increasing the number of sol coatings. All PZT thick films showed the typical X-ray diffraction patterns of a perovskite polycrystalline structure. The thickness of all thick films was approximately 60–61 μm. The relative dielectric constant increased and dielectric loss decreased with increasing the number of sol coatings, and the values of the six-layer PZT-6 film were 167.8, 0.78% at 1 kHz, respectively. The remanent polarization and coercive field of the 6-coated PZT-6 thick films were 14.1 μC/cm2 and 20.3 kV/cm, respectively.

Structural and Electrical Properties of (Ba,Sr,Ca)TiO 3 Thick Films doped with Dy 2 O 3

In this study, we investigated the effects of structural and electrical properties of thick films with variation contents. powders, prepared by the sol-gel method, were mixed organic vehicle. The BSCT thick films doped with 0.1, 0.3, 0.5, 0.7 mol% were fabricated by the screen-printing techniques on the alumina substrates and the structural and dielectric properties were investigated with variation of doping contents. All BSCT thick films were sintered at , for 2hr. In the TG-DTA analysis, the formation of the polycrystalline perovskite phase was observed at around . In the XRD analysis, all BSCT thick films showed the cubic perovskite structure. The average thickness of BSCT thick films was approximately . The Curie temperature decreased with increasing amount. The relative dielectric constant and dielectric loss of BSCT thick films doped with 0.1 mol% were 6267 and 2.6 %, respectively.

Structural and Electrical Properties of Pb(Zr 0.4 Ti 0.6 O 3 /PbZr 0.6 Ti 0.4 )O 3 Heterolayered Thick Films

[ ] paste were made and alternately screen-printed on the substrates. We have introduced a press-treatment to obtain a good densification of screen printed films. The porosity of the thick films was decreased with increasing the applied pressure and the thick films pressed at 60 MPa showed the dense microstructure and thickness of about . The remanent polarization and coercive field increased with increasing applied pressure and the values for the PZT thick films pressed at 60 MPa were and 78.09 kV/cm, respectively.

Effect of Composition and Coating of Precursor Solution on a Micro Structural Properties of PZT Thick Films

The influence of the number of solution coatings on the densification of the PZT thick films was studied. PZT powder and PZT precursor solution was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The powder and solution of composition were (A) PZT(80/20)/PZT(20/80), (B) PZT(70/30)/PZT(30/70) and (C) PZT(60/40)/PZT(40/60), (D) PZT(52/48)/PT. The coating and drying procedure was repeated 4 times. And then the PZT precursor solution was spin-coated on the PZT thick films. A concentration of a coating solution was 0.5 moth and the number of coating was repeated from 0 to 6. The porosity of the thick films was decreased with increasing the number of coatings and the PZT thick films with 6-times coated showed the dense microstructure and thickness of about . A grain size was increased with increasing the coating number. All PZT thick films showed the typical XRD patterns of a typical perovskite polycrystalline structure. The relative dielectric constant of PZT thick films was improved 30-100% as the number of coatings.