Byung-Kook Kim

Quantitative phase analysis in tetragonal-rich tetragonal/monoclinic two phase zirconia by Raman spectroscopy

Abstracts are not published in this journal

Mode Assignments of the Raman Spectrum of Monoclinic Zirconia by Isotopic Exchange Technique

The mode assignments of the sixteen Raman bands observed for monoclinic zirconia (ZrO 2 ) have been made by measuring the Raman spectra of the cationic- as well as the anionic-labelled compounds, that is, 91.22 Zr( 16 O 1-x 18 O x ) 2 (x = 0.002 to 0.760) and 93.80 Zr 16 O 2 . The four Raman bands at 334, 224, 192, and 180 cm -1 were not influenced by the 16 O- 18 O substitution but were shifted to lower wavenumbers by the 91.22 Zr- 93.80 Zr substitution, from which they are assigned to the Zr-Zr vibrations. The three Raman bands at 380, 349, and 308 cm -1 were shifted to lower wavenumbers by the 91.22 Zr- 93.80 Zr as well as the 16 O- 18 O substitution, from which they are assigned to the Zr-O vibrations. The eight Raman bands at 800 to 382 cm -1 and the band at 105 cm -1 were shifted to lower wavenumbers by the 16 O- 18 O substitution but were shifted to higher wavenumbers by the 91.22 Zr- 93.80 Zr substitution, from which they are assigned to the O-O vibrations.

Nanotransport in polyacetylene single fiber: Toward the intrinsic properties

The electrical transport properties of iodine doped polyacetylene (PA) nanofibers were measured as function of temperature in micron and sub-micron scale. Polyacetylenc fiber network measured in micron scale shows weaker temperature dependence of resistivity and smaller negative magnetoresistance (MR) at T=1.5K compared to those of hulk PA film. The reaction of Au electrodes with dopant became serious in submicron experiment, so that stripes of Pt electrodes with 100nm separation were patterned on top of the SiO 2 substrate to prevent the reaction. Non-ohmic I-V charactersitics are observed in PA nanofiber. The gate dependence shows the charge carrier to be hole with mobility μ FET ∼ 4.4×10 -5 cm 2 /Vs at 233K. The non-ohmic I-V dependence at high electric fields could be originated from the soliton tunneling conduction in PA nanofiber.

Piezoelectric properties in PMN–PT relaxor ferroelectrics with MnO2 addition

Abstract The temperature dependence of piezoelectric properties in the PMN–PT relaxor ferroelectric system with MnO 2 addition was studied in the temperature range from −40 to 30°C. Samples were poled at −40°C and the piezoelectric properties were measured by resonance–antiresonance method. Q m increased by increasing the doping contents of Mn. When 0.5 wt.% MnO 2 was doped, Q m increased from 95 to 480. From the experimental results, it is predicted that Mn behaves as an acceptor and a domain pinning element. The effects of MnO 2 observed in PZT-based normal ferroelectrics were also confirmed in PMN-based relaxor ferroelectrics.

Electric-field induced strains and pyroelectric coefficients in lead magnesium niobate-lead titanate solid solutions

Abstract In order to understand the electrostrictive behavior of Pb(Mg 1 3 Nb 2 3 )O 3 -PbTiO 3 (PMN-PT ) solid solutions, the dielectric constants, the electric field induced strains, the electric-field induced polarization, and the pyroelectric coefficients of (1 − x)PMN-xPT (x = 0.1 ~ 0.4) were investigated in the temperature range −50 °C ~ 200 °C. For x = 0.1 ~ 0.35, where the phase transition is diffuse, the strain has a maxima at the temperature of maximum pyroelectric coefficient (depolarizing temperature) rather than the temperature of maximum dielectric constant (Curie temperature). For x = 0.4, where the phase transition is relatively sharp, the strain decreases monotonically as the temperature increases. Relationships among the above experimental results are discussed.

Gating effect in the I-V characteristics of iodine doped polyacetylene nanofibers

The I-V characteristics of iodine doped polyacetylene (PA) nanofibers were measured as function of temperature. Platinum electrodes on top of SiO 2 substrates were used to prevent reaction with iodine dopant. The distance between the two electrodes is approximately 100 nm. Upon iodine doping, non-ohmic I-V characteristics are observed. The gate dependence shows the charge carrier to be hole with a mobility μ FET ∼ 4.4×10 -5 cm 2 /Vs at 233K.

Raman spectrum of 18O-labelled Hafnia

The Raman spectrum of {sup 18}O-labelled monoclinic Hafnia (HfO{sub 2}) is reported. All of the eighteen Raman bands predicted from a group theoretical analysis are observed. The six Raman bands at 300--130 cm{sup {minus}1} have little dependence on the {sup 18}O content, whereas the remaining twelve Raman bands shift to low wavenumbers by the {sup 18}O-substitution. The former six are assigned to the Hf-Hf vibrations and the latter twelve are assigned to the Hf-O or O-O vibrations.

Enhanced oxygen diffusion in epitaxial lanthanum–strontium–cobaltite thin film cathodes for micro solid oxide fuel cells

The chemical diffusion coefficient (Dchem) of epitaxial LSC thin films was measured by a newly designed conductivity relaxation method. Dchem of epitaxial thin films was found to be higher than that of bulk LSC by up to two orders of magnitude, and was found to be enhanced further as the film became thinner.

Outcome of Adult Severe or Very Severe Aplastic Anemia Treated with Immunosuppressive Therapy Compared with Bone Marrow Transplantation : Multicenter Trial

To compare survival rates and long-term complications after bone marrow transplantation (BMT) or treatment with immunosuppressive agents (ISA) in the management of adult aplastic anemia (AA) and to identify prognostic factors associated with improved survival, we evaluated 229 adult AA patients treated with ISA from 1990 to 2001 and compared the results with those for 64 BMT recipients. Of 156 patients with severe aplastic anemia (SAA) or very severe AA treated with ISA (antithymocyte globulin [ATG]or ATG plus cyclosporine), 46.8% showed complete or partial response and 7.1% had relapses. After long-term follow-up, 1 case each of acute leukemia, myelodysplastic syndrome, and paroxysmal nocturnal hemoglobinuria developed.The 6-year survival rate was 69%. Response to ISA, disease severity, and low absolute neutrophil count (ANC) (≤200/mm3) were associated with poor survival. Patient age, sex, initial platelet count, etiology, or treatment regimen did not significantly affect survival. Cox regression analysis showed low ANC to be the only pretreatment variable significantly associated with poor survival (P = .000). Of 64 BMT recipients, 82.8% had sustained engraftment, and 12.5% experienced graft failure. Twenty (31.3%) of the patients developed grade II to IV acute graft-versus-host disease (GVHD), and 12 (18.8%) of the patients developed chronic GVHD.The 6-year survival rate was 79%. Patient age and sex, disease severity, etiology,ANC, initial platelet count, and treatment regimen did not affect survival. Survival of 83 AA patients, aged 14 to 40 years, treated with ISA was not statistically significant from that of 61 adult AA patients who underwent BMT (6-year survival rate, 65% and 79%, respectively). However, BMT in adult AA achieved long-term engraftment and a lower relapse rate than ISA.These results suggest that ISA can achieve a high response rate and long-term survival among patients with adult AA,regardless of disease severity. Further studies with larger numbers of patients and long-term follow-up are needed.

Effect of microstructure on the microwave properties in dielectric ceramics

Abstract Electromagnetic simulation of the quality factor measurement was compared to the measurement with a network analyzer. Scattering matrix S 21 obtained from the network analyzer was compared to the S 21 obtained from the simulation. From electric field distribution, the dominant resonant TE 01δ mode could be easily determined. The effects of the pore and the conductive inclusion inside the dielectric were investigated. The quality factor decreased with the pore and the second phase in the dielectrics. The decrease of quality factor is more significant when dielectric have conductive inclusions inside the dielectric. Due to the limitations in computer resources and analysis time, the size of the inclusions inside the dielectrics in simulation are not actual size.