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pISSN : 1225-1429 / eISSN : 2234-5078

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2015, Vol.25, No.4

  • 1.

    Microstructure analyses of aluminum nitride (AlN) using transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD)

    주영준 | 박청호 | 정주진 and 4other persons | 2015, 25(4) | pp.127~134 | number of Cited : 3
    Abstract PDF
    Aluminum nitride (AlN) single crystals have attracted much attention for a next-generation semiconductor application because of wide bandgap (6.2 eV), high thermal conductivity (285W/m · K), high electrical resistivity (≥ 10 14 Ω · cm), and high mechanical strength. The bulk AlN single crystals or thin film templates have been mainly grown by PVT (sublimation) method, flux method, solution growth method, and hydride vapor phase epitaxy (HVPE) method. Since AlN suffers difficulty in commercialization due to the defects that occur during single crystal growth, crystalline quality improvement via defects analyses is necessary. Etch pit density (EPD) analysis showed that the growth misorientations and the defects in the AlN surface exist. Transmission electron microscopy (TEM) and electron back-scattered diffraction (EBSD) analyses were employed to investigate the overall crystalline quality and various kinds of defects. TEM studies show that the morphology of the AlN is clearly influenced by stacking fault, dislocation, second phase, etc. In addition EBSD analysis also showed that the zinc blende polymorph of AlN exists as a growth defects resulting in dislocation initiator.
  • 2.

    Thermoelectric properties of Bi2Te2.7Se0.3 grown by traveling heater method

    Im-Jun Roh | 현도빈 | Kim Jin Sang | 2015, 25(4) | pp.135~139 | number of Cited : 0
    Abstract PDF
    Bi2Te3-Bi2Se3 alloy which is typical n-type thermoelectric material were grown by traveling heater method (THM) technique. We investigate the effect of the composition of 100-x(Bi2Te3) - x(Bi2Se3) and doping of n-type dopants such as SbI3 and CdCl2. Maximum figure of merit of Bi2Te3-Bi2Se3 alloy was observed with CdCl2 0.1 wt% (Z: 2.73 × 10−3 / K) and SbI3 0.05 wt% (Z: 2.29 × 10−3 /K). Deviation along the length of Bi2Te3-Bi2Se3 ingot grown by THM method is low, which indicates that the ingot is very homogenized. Also we observed the close relationship of between anisotropy ratio and dopant in the 90(Bi2Te3) - 10(Bi2Se3) alloys. And we confirmed the fact that anisotropy ratio exerts thermoelectric performance in Bi2Te3 based n-type thermoelectric material.
  • 3.

    Optimization of head mass for tonpilz transducer using finite element method

    서진원 | Kyoon Choi | LEE HO YONG | 2015, 25(4) | pp.140~144 | number of Cited : 2
    Abstract PDF
    Effects of the shape, the size and the material of head mass on performances of tonpilz transducer were studied with a finite element method. The shape of head mass was changed with an angle between symmetric axis and side of head mass of transducer from 0 to 60 degree. As a result of the simulations, the bandwidth leached to 86.4 % at 35.5 degree in case of Al head mass. The size of head mass showed a decrease in the power of transducer with little change of bandwidth. For the Ti head mass, the transmitted power showed 100 % increase with a bandwidth of 88.1 % even though the weight of the head mass increased to 167 % of Al. This can be attributed to the mechanical properties like elastic modulus of Ti relative to Al.
  • 4.

    Effect of the additive gas on the bonding structure and mechanical properties of the DLC films deposited by RF-PECVD

    Bonggeun Choi | 2015, 25(4) | pp.145~152 | number of Cited : 0
    Abstract PDF
    In this work, we were investigated the effect of the additive gases on the relationship between bonding structure and mechanical properties of the deposited films when the DLC films were deposited on Si-wafer by the rf-PECVD method with the addition of small amounts of carbon dioxide and nitrogen to the mixture gas of methane and hydrogen. The deposition rate of the films increased as the rf-power increased, while it decreased with increasing the amount of additive gases. Also, as the carbon dioxide gas increased, the hydrogen content in the films decreased but the sp 3 /sp 2 ratio of the films increased. In case of nitrogen gas, the hydrogen content decreased, however the sp 3 /sp 2 ratio and nitrogen gas flow rate did not show a specific tendency.
  • 5.

    Effect of Bi and Zr addition on yellow colour properties of environmentfriendly ceria-based pigments

    Tae-Ho Kim | HAE JIN HWANG | Jinho Kim and 2other persons | 2015, 25(4) | pp.153~159 | number of Cited : 4
    Abstract PDF
    Inorganic pigments have been received a great attention for various applications including paint, glazed ceramic ink, art tile, and building exterior due to their excellent thermal and chemical stability. Traditionally, the compositions of PbCrO4, CdS and CdSe have been widely used as a yellow inorganic pigment. However, the use of these compositions has been restricted in recent years, because they contain harmful elements such as Cd, Cr, Pb and Se. In this study, new environment-friendly ceria-based pigment was synthesized using solid state reaction. Crystal structure and morphology of the obtained Ce1 − xZrxBiyO2 − y/2 yellow pigment were analyzed using XRD and SEM, respectively. Substitutional effect of Zr and Bi on the pigment color was analyzed using UV-vis. spectrophotometer and CIE L*a*b* analysis. The crystal structure of the obtained pigments was dependent on the calcination temperature. The color characteristics and absorption band of the pigments were dependent on the calcination temperature and Zr, Bi contents. As a result, all the obtained yellow pigments showed the effective absorption ranged from ultraviolet to visible light, and Ce0.44Zr0.36Bi0.20O0.19 (x = 0.36, y = 0.20) pigment showed the most brilliant yellow color.
  • 6.

    Processing, structure, and properties of lead-free piezoelectric NBT-BT

    민성욱 | Lee, Jung-il | Ryu, Jeong-ho | 2015, 25(4) | pp.160~165 | number of Cited : 0
    Abstract PDF
    Lead-free piezoelectric materials have been actively studied to substitute for conventional PZT based solid solution, Pb(ZrxTi1 − xO3), which occurs unavoidable PbO during the sintering process. Among them, Bismuth Sodium Titanate, Na0.5Bi0.5TiO3 (abbreviated as NBT) based solid solution is attracted for the one of excellent candidates which shows the strong ferroelectricity, Curie temperature (Tc), remnant polarization (Pr) and coercive field (Ec). Especially, the solid solution of rhombohedral phase NBT with tetragonal perovskite phase has a rhombohedral - tetragonal morphotropic phase boundary. Modified NBT with tetragonal perovskite at the region of MPB can be applied for high frequency ultrasonic application because of not only its low permittivity, high electrocoupling factor and high mechanical strength, but also effective piezoelectric activity by poling. In this study, solid state ceramic processing of NBT and modified NBT, (Na0.5Bi0.5)0.93Ba0.7TiO3 (abbreviated as NBT-7BT), at the region of MPB using 7 % BaTiO3 as a tetragonal perovskite was introduced and the structure between NBT and NBT-7BT were analyzed using rietveld refinement. Also, the ferroelectric and piezoelectric properties of NBT-7BT such as permittivity, piezoelectric constant, polarization hysteresis and strain hysteresis loop were compared with those of pure NBT.
  • 7.

    Fabrication of YAG : Er 3+ powders for the single crystal growth according to the synthetic temperature and flux concentration

    Cheol Woo Park | 강석현 | 박재화 and 4other persons | 2015, 25(4) | pp.166~171 | number of Cited : 0
    Abstract PDF
    In this study, using solid-state and flux, Y3Al5O12 : Er 3+ (YAG : Er 3+ ) powders were successfully synthesized at low temperatures. To analyze the crystallinity of powders according to the synthesis or non-synthesis of powders and powder calcination temperatures, X-ray diffraction (XRD) was measured. In the case of pure YAG, when YAG was analyzed using the general solid-phase method, it was calcined for 12 hours at 1400 o C and pure YAG phase could be obtained. But when BaF2 was added to YAG, YAG was synthesized at lower temperature (1000 o C). It was thus found that the synthesis temperature could be lowered by about 400 o C. Also, when BaF2 with an optimal concentration was added to YAG : Er 3+ , the particle shape and size according to synthesis temperatures were surveyed, and corresponding luminous intensity was discussed.