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- 저자 : Donggun Gwoo (검색결과 7 건)
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Electrical Properties of Crystallized 30B2O3-70V2O5 Glass
Donggun Gwoo,김태희,한경석,Wongyu Choi,김종환,류봉기 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.3
30B2O3-70V2O5 binary-system glass was prepared, and variations in structural and electrical property were examined using crystallization. While different related research studies exist, few have evaluated the variations in the structure and properties with changes in the crystallization rate. 30B2O3-70V2O5 glass was annealed in the graphite mold above the glass transition temperature for 2 h and heat-treated at each crystallization temperature for 3 h. 30B2O3-70V2O5 glass showed predominantly electronic conductive characteristic. FTIR was preferentially used for analyzing the structural changes of B-O bond after crystallization, while XRD was utilized to verify the inferred changes in the structure array (BO3 + V2O5 ↔ BO4 + 2VO2). Structural changes induced by heat treatment were confirmed by analyzing the molecular volume determined from the sample density, and conductance was measured to correlate structural and property changes. Conductivity is discussed based on the migration of vanadate ions with different valence states because of the increase in VO2 crystallinity at 130°C, which, however, was not observed at 170°C. After VO2 structures were reinforced,a 1.8-fold increase in conductance was observed (as compared to the annealed sample) after crystallization at 130°C for 3 h.
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Relationship between Structure and Optical Properties in the CdO-B2O3-SiO2 Glass System
Taehee Kim,Donggun Gwoo,김종환,Wongyu Choi,Kyungseok Han,Kyungbum Kee,황차원,류봉기 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.6
To study the compositional dependence of the optical properties and atomic structure of glasses, the CdOB2O3-SiO2 ternary glasses, which are known as highly photoconductive glasses, have been investigated. The photoconductivity of glasses containing CdO was investigated in a previous study, because of their potential applications in photoelectronic devices. The thermo-mechanical analysis and the Fourier transform infrared (FT-IR) spectra of the glass samples were measured to determine the structural variation of these glasses. Using transmittance measurements, we calculated the optical energy band gap. This paper presents results for control of the optical energy band gap 3.8 ~ 3.2 eV in cadmium-borosilicate glass system while the structural properties undergo monotonic changes.
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A Study of the Relationship between Structure and Properties of Cadmium Phosphate Glasses
Wongyu Choi,Taehee Kim,Donggun Gwoo,Kyungbum Kee,Jong-Hwan Kim,Kyung-Suk Han,류봉기 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.1
It analysed the structure and chemical durability which it follows in CdO content in Cadmium phosphate glasses. We prepared glasses with the composition, xCdO-(100-x)P2O5 (x = 10 mol. % to 50 mol. %), and analyzed their density (ρ), molar volume (VM), glass transition/softening temperature (Tg/Td), thermal expansion coefficient (α), fourier transform infrared spectroscopy, and dissolution rate. All of these of the values were found to vary with the CdO content of the glasses. It is observed that the dissolution rate increase with with CdO contents. This suggests that Cadmium ion breaks the p-o-p bonds.
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Synthesis and Characterization of CdS Nanocrystals in a Novel Phosphate Glass
Donghwan Kim,Chawon Hwang,Donggun Gwoo,Taehee Kim,Youngseok Kim,Namjin Kim,류봉기 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.4
Zinc-borophosphate glasses doped with various concentrations (≤ 5 wt. %) of cadmium sulfide (CdS) were synthesized. Nanocrystals of CdS were developed in the glass matrices at different concentrations, with emphasis on the quantum confinement effect. The effects of CdS content on the optical and various other properties were investigated. The optical characterization of the glasses was carried out using UV-Visible spectrophotometry. There was a red shift in the optical cut-off with increasing CdS content in the glass. The band gap of the CdS nanocrystals doped in the glass matrix ranged from 3.5 eV to 4.2 eV. The structural characterization,which was carried out using X-ray diffraction, shows the CdS to have hexagonal crystal structure. The average size and shape of the nanocrystals doped in the glass matrix were determined using transmission electron microscopy (TEM). The particle sizes of the doped CdS crystals were in the range of 3 nm to 6 nm for 2 wt. % CdS, and 15 nm to 20 nm for 5 wt. % CdS.
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Effect of Titanium on Structure of Sodium Borophosphate Glasses
Donghwan Kim,Chawon Hwang,Donggun Gwoo,Taehee Kim,Namjin Kim,류봉기 대한금속·재료학회 2011 ELECTRONIC MATERIALS LETTERS Vol.7 No.4
Glasses in the system 30P₂O_5-30B₂O₃-40Na₂O-xTiO₂ (0 ≤ x ≤ 25 mol %) have been prepared by the meltquenching technique. Increasing the TiO₂ content of the glass structure results in a decrease in the molar volume and an increase in the glass transition/softening temperatures. Structural changes were studied by Raman spectroscopy, and 11 B and 31P solid-state NMR. The observed changes in the spectra and the properties of the studied glasses can be ascribed to several reasons, such as the addition of TiO₂ that results in the formation of distorted Ti octahedral linked to pyrophosphate unit through P–O–Ti bonds. In these glass series,the overall glass network was enhanced by TiO₂ addition, although a depolymerization in the original P–O–P network occurred.
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Effects of Substitution of K2O for Na2O on the Bioactivity of CaO-Na2O-SiO2-P2O5 Glasses
Taehee Kim,Chawon Hwang,Donggun Gwoo,Hoyyul Park,류봉기 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.5
The compositional dependences of bioactivity, thermal properties, atomic structure, and surface morphology have been investigated in the CaO-Na2O-SiO2-P2O5 system; this system is known as a bioglass. 45S5 Bioglass®is known to be a general and highly bioactive material. However, the bioactivity of this glassy material is expected to be improved by modifying the alkali-metal composition. Thermal properties, density, and molar volume were measured to investigate the structural packing. FT-IR spectra and X-ray diffraction were used to confirm the structures of these glasses. The morphology was examined using field emission electron microscopy,and the formation of a Ca-P layer was studied using an energy-dispersive system. This study shows that the tendency to form a calcium phosphate layer is increased with the substitution of K2O for Na2O.
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Effects of Substituting B2O3 for P2O5 on the Structures and Properties of V2O5-P2O5 Glass Systems
Kyungseok Han,황차원,Dong Hwan Kim,Donggun Gwoo,Taehee Kim,Wongyu Choi,Kyungbum Kee,김종환,류봉기 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.6
V2O5-B2O3-P2O5 glasses with various compositions were prepared using a normal melt quenching technique,and their characteristics and structural properties were investigated using different techniques. Replacement of P2O5 by B2O3 was found to improve the thermal properties, chemical durability, and room-temperature conductivity. The observed variations in the properties may be correlated with changes in the internal glass network as a result of changes in the chemical composition. Vanadium ions are believed to be present in three possible valence states, namely V3+, V4+, and V5+, and the ratios of these states depend on the glass composition. The observed increases in chemical durability and room-temperature conductivity are assumed to be related to increases in the mean crosslinking density, increases in the number of bridging oxygens,and electron hopping between vanadate ions in different valence states.
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