Sung Gap Lee

Dielectric properties of Pb(Zr,Ti)O3 heterolayered films prepared by sol-gel method

Ferroelectric Pb(Zr,Ti)O3 (PZT) heterolayered thin films were fabricated by the alkoxide-based sol–gel method. PZT (20/80) and PZT (80/20) stock solutions were made and alternately spin-coated on the Pt/Ti/SiO2/Si substrate. Each layer was dried at 300°C for 30 min and sintered at 650°C for 1 h. The coating and heating procedure was repeated 6 times to form heterolayered films. PZT film thickness, obtained by one cycle of drying/sintering, was approximately 80 nm. The PZT heterolayered films showed dense and fine grain structures with a grain size of less than 0.2 µm. The relative dielectric constant and the dielectric loss of the 6-coated PZT heterolayered film(PZT-6) were approximately 1385 and 3.3%, respectively. As the number of coatings increased, remanent polarization increased, the coercive field decreased and the values for the PZT-6 film were 8.13 µC/cm2 and 12.5 kV/cm, respectively. The leakage current density of the PZT-6 film at 5 V was 8.8 ×10-13 A/cm2.

Preparation and Characterization of Lead Zirconate Titanate Heterolayered Thin Films on Pt/Ti/SiO2/Si Substrate by Sol–Gel Method

Ferroelectric Pb(ZrxTi1-x)O3 (PZT; x=0.2, 0.8) heterolayered thin films were fabricated by the spin-coating method on the Pt electrode alternately using PZT(20/80) and PZT(80/20) metal alkoxide solutions. All PZT heterolayered films show dense structure without the presence of the rosette structure. The lower PZT layers provide the nucleation site for the formation of a perovskite phase in the upper PZT films. Pb-deficient pyrochlore phase was formed at PZT/Pt interface due to diffusion of the Pb element into the Pt bottom electrode. The relative dielectric constant and dielectric loss of the six coated PZT heterolayered film were approximately 1385 and 3.3% at 1 kHz, respectively.

Structural and Dielectric Properties of Screen Printed PZT(70/30) Multilayered Thick Films

PZT(70/30) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The coating and drying procedure was repeated 4 times. And then the PZT(30/70) precusor solution was spin-coated on the PZT thick films. A concentration of a coating solution was 0.5 mol/L and the number of coating was varied from 0 to 6. The porosity decreased and the grain size increased with increasing the number of coatings. The thickness of the PZT-6(6: number of coatings) films was about 60~65μm. All PZT thick films showed the typical XRD patterns of a typical perovskite polycrystalline structure. The relative dielectric constant of the PZT-6 thick film was 540. The remanent polarization and coercive field of the PZT-6 film were 23.6 μC /cm2, 12.0 kV/cm, respectively.

Structural and Electrical Properties of Vanadium Tungsten Oxide Thin Films Grown on Pt/TiO2/SiO2/Si Substrates

The V1.9W0.1O5 thin films deposited on Pt/Ti/SiO2/Si substrates by RF sputtering method exhibited fairly good TCR and dielectric properties. It was found that film crystallinity, dielectric properties, and TCR properties were strongly dependent upon the annealing temperature. The dielectric constants of the V1.9W0.1O5 thin films annealed at 300°C were 37.7, with a dielectric loss of 2.535, respectively. Also, the TCR values of the V1.9W0.1O5 thin films annealed at 300°C were about -3.7%/K.

Pyroelectric Properties of Lead Antimony Stannate-Lead Titanate-Lead Zirconate Ceramics Modified with La and Mn

In the present study, 0.10Pb(Sb1/2Sn1/2)O3-0.25PbTiO3-0.65PbZrO3 ceramics modified with La2O3 (1 mol%) and MnO2 (0~0.30 mol%) were fabricated, and the structural and pyroelectric properties with different amounts of MnO2 were studied. The crystal structure of specimens was rhombohedral, and average grain sizes decreased with increasing amounts of MnO2. The (Pb0.99La0.01)[(Sb1/2Sn1/2)0.10Ti0.25Zr0.65]O3 specimen modified with 0.24 mol% MnO2 showed a large pyroelectric coefficient, p, (=6.73×10-8 C/cm2 K) and voltage responsivity, Rv, (=125 V/W). Also, in the same specimens, noise equivalent power, NEP, and detectivity, D*, were 2.376×10-7 W/Hz1/2 and 6.793×106 cm Hz1/2 W, respectively. In the (Pb0.99La0.01)[(Sb1/2Sn1/2)0.10Ti0.25Zr0.65]O3 specimens modified with 0.24 mol% MnO2 voltage responsivity decreased with increasing chopper frequency, and was independent of the thickness of the specimens.

Electrical Properties BaTiO3 Thick Films with an Interlayer SrTiO3 Thin Films

The BaTiO3/SrTiO3 heterolayered thick films were fabricated by two different methods – thick films of BaTiO3 by screen printing method on alumina substrates electrodes with Pt, thin films of SrTiO3 by the spin-coating method on BaTiO3 thick films and once more thick films of BaTiO3 by the screen printing method on SrTiO3 layer. The leakage current and the dielectric properties were investigated for effect of various stacking sequence of sol-gel-prepared SrTiO3 layer at interface of BaTiO3 thick films. The insertion of SrTiO3 interlayer yielded BaTiO3 thick films with homogeneous and dense grain structure with the number of SrTiO3 layers. The leakage current density of the BaTiO3/SrTiO3-7 film is less that 1.5 10-9 A/cm2 at 5 V.

Microstructure Analysis and Characterization of Li(Ni1-xCox)O2 Thin Film Prepared by Li Diffusion on Ni-Co Alloy Substrates for Cathode Application

The currently commercialized cathode material for Li ion batteries such as LiCoO2 exhibited limit to further improve the performance of the batteries, since the employed screen printing method for cathode fabrication is difficult to reduce the thickness and control the microstructure of the oxide layer. In this studies, we have synthesized Li(Ni1-xCox)O2 thin film by utilizing Li-diffusion reaction on the surface of Ni-Co alloy substrates. For the preparation of Ni-Co alloy rod, Ni and 20at.%Co powder were mixed for 24hrs by ball milling, and then pressed into rod-shape by cold-isostatic pressing. The Ni-Co rods were sintered at 1100°C for 6hrs in the reducing atmosphere of Ar 96% and H2 4%. The sintered Ni-20at%Co rod was cold-rolled into tape at 5% reduction ratio with the final thickness of 100㎛, and the recrystallization heat treatment for the development of the cube texture of the rolled Ni alloy tape was carried out at 1000°C in Ar 96% and H2 4%. After thin layer of metallic Li was deposited on the surface of Ni-Co template using thermal evaporation method in the glove box, the Li/Ni-Co composite tape were heat-treated at 700~850°C for 1~2hrs in oxidizing atmosphere to induce Li-diffusion into Ni-Co substrate and Li(Ni0.8Co0.2)O2 phase formation. The phase evolution of Li(Ni0.8Co0.2)O2 was confirmed by X-ray diffraction and the grain size and morphology of the surface were analyzed by scanning electron microscopy and atomic force microscopy. Also the charge and discharge test were conducted to confirm the electrical characteristics of Li(Ni1-xCox)O2/Ni-Co thin film for the cathode application.

Structural and Electrical Properties of Lead Zirconate Titanate Thick Films Fabricated by Screen-Printing Method

Ferroelectric Pb(Zr0.6Ti0.4)O3 (PZT(60/40)) powder was prepared by a sol-gel method and PZT thick films were fabricated by the screen-printing method on the alumina substrates. The Pt bottom electrodes were screen-printed on the alumina substrate. The PZT(60/40) thick films were annealed at 1050°C for 10min in PbO atmosphere. Pb(Zr0.4Ti0.6)O3 (PZT(40/60)) precursor solution, which prepared by sol-gel method, was spin-coated on the PZT thick films to obtain a densification. These PZT multilayered thick films were annealed at 650°C for 2 h in PbO atmosphere. The upper electrodes were fabricated by screen printing the Ag paste and then firing at 590°C for 10min. Its structural and electrical properties of the PZT thick films with the treatment of PZT(40/60) precursor solution coating were investigated. The coating and drying procedure was repeated 4 times. And then the PZT(40/60) precursor solution was spin-coated on the multilayered thick films. A concentration of a coating solution was 1.5 mol/L and the number of coating was repeated from 0~15. The porosity of the thick films was decreased with increasing the number of coatings. All PZT multilayered thick films showed the XRD patterns of typical peroveskite polycrystalline structure. The relative dielectric constant of the PZT-15 (15: number of solution coatings) thick film were 370. And the PZT-15 thick film shows the remanent polarization of 23.5 μC/cm2 and coercive field of 18.0 kV/cm, respectively.

Dielectric Properties of Sol Infiltrated Lead Zirconate Titanate Ferroelectric Thick Films

Ferroelectric PZT(70/30) thick films were fabricated by the hybrid technique adding the sol coating process to the screen-printing process to obtain a good densification. Structural and electrical properties of the thick films with the sol concentration were investigated. The relative dielectric constant increased and dielectric loss decreased with increasing the sol concentration, the values of the thick film coated with sol concentration of 1.5 M were 698 and 2.5 % at 1 kHz, respectively. And the remanent polarization and dielectric breakdown strength of the thick film coated with sol concentration of 1.5 M were about 38 μC/cm2 and 200 kV/cm, respectively. The leakage current densities were less than 10-8 A/cm2 at the applied electric field range of 0-100 kV/cm in all thick films.

Densification of Unfired Alumina Refractories by the In Situ Spinel Formation during Application

To prevent the shrinkages by the densification during the application of unfired Al2O3-C refractories or Al2O3 castables in steel making conditions, MgO was added as aggregate or matrix powder and the expansion caused by spinel formation was studied. Because the spinel was formed at the contacting areas between Al2O3 and MgO particles and the volume of in-situ formed spinel increased more abnormally at the side of Al2O3 particles than MgO, the addition of MgO aggregates was not recommendable due to the formation of large voids around the MgO aggregates. Nevertheless, corrosion resistance was increased with the amount of fine MgO added, and the finer MgO powder added, the better residual expansion and minute structure formation was observed. In the contrary, in case of castables volume expansion due to spinel formation was not obvious because the degree of densification was less than high-pressure formed refractories. But CA6 phase would not form around alumina aggregates during corrosion so the corrosion resistance was much more enhanced.