• 한국초전도학회:학술대회논문집
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• v.9
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• pp.95-98
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• 1999

The crystalline alignment of Ni substrates textured by RABiTS have a probability distribution in the surface plane. This makes it difficult to obtain a high quality of textures over all the range of a long Ni tape. In order to improve the textures of Ni tape, we have investigated a new method of texturing. We obtained non-cube textured Ni tapes by rolling and annealing a high purity Ni. In these tapes, the [001]-axes were tilted around the rolling direction, and the [100]-axes were parallel to the rolling direction. The average grain size was several cm$^2$. We deposited buffer layer (CeO$^2$/YSZ/CeO$^2$) and YBCO on those tapes. We found out that a YBCO film with grows normal with respect to the surface and this feature is independent of the tilting angles of the Ni [001]-axes.

• Journal of the Korean Ceramic Society
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• v.32 no.6
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• pp.726-734
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• 1995

Pb(Zr0.53Ti0.47)O3 (PZT) ceramics having different microstructures were fabricated at low temperatures using calcined PZT powders with addition of excess PbO powder and/or ball milling. The effects of excess PbO and ball milling time on the microstructure, the sintering characteristic, and the mechanical properties of these ceramics were studied. Fine powders with average particle size of 0.38㎛ could be obtained by ball milling with 2.5 mm Ф zirconia balls for 120 hours. By the addition of 2mol% of excess PbO to these powders, it was possible to obtain well-densitified PZT ceramics at low sintering temperature of 980℃. Densification behavior of PZT was affected by the addition of excess PbO powder, while, grain growth was hardly affected by PbO addition. It was observed that Vicker's hardness decreased and fracture toughness increased with the increasing amount of PbO. At 1mol% excess PbO, it was shown that the minimum values of hardness and maximum fracture toughness were achieved. In addition, with increasing sintering time, the fracture toughness decreased and the hardness increased.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.07a
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• pp.383-386
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• 2002

Polycrystalline Cu(In,Ga)Se$_2$(CIGS) thin-films were grown by co-evaporation on a soda lime glass substrate. In this paper the effects of the Se evaporation temperature on the properties of CuIn0.75Ga0.25Se2 (CIGS) thin films. Structure, surface morphology and optical properties of CIGS thin films deposited at various Se evaporation temperatures have been investigated using a number of analysis techniques. X-ray diffraction (XRD) analysis shows that CIGS films exhibit a strong <112> preferred orientation. As expected, at higher Se evaporation temperatures the films displayed a lower degree of crystallinity. The <112> peak was also enhanced and other CIGS peaks appeared simultaneously. These results were supported by experimental work using scanning electron microscopy When the Se evaporation temperature was increased, the average grain size also decreased together with a reduction Cu content. The Se evaporation temperature also had a significant inf1uence on the transmission spectra. Increasing the Se evaporation temperature, the cell efficiency was improved dramatically to 11.75% with Voc = 556 mV, Jsc = 32.17 mA/cm2 and FF = 0.66. The Se evaporation temperature is an important parameter in thin film deposition regardless of the deposition technique being used to deposit thin films

• Journal of the Korean Ceramic Society
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• v.26 no.1
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• pp.123-131
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• 1989

Hydroxyapatite powders were syntehsized by the reaction of Ca(NO3)2.4H2O and (NH4)2HPO4 in aqueous solution. The effect of the Ca/P mole ratio in the starting solution on the sintering of the powders and its microstructure was studied. When the Ca/P mole ratio in the starting solution was 1.69, the relative density of the sintered bodies was more than 95%. The sinterability was decreased as the Ca/P mole ratio in the starting solution was increased (Ca/P mole ratio >1.67). Hydroxyapatite sintered bodies obtained from the Ca/P mole ratio=1.69 had very excellent bending strength. The best bending strength was obtained at 110$0^{\circ}C$ and its value was 1220kg/$\textrm{cm}^2$. The average grain size was 0.277${\mu}{\textrm}{m}$. Most of sintered bodies were almost shown 100% hydroxyapatite phase. However, in case of the Ca/P mole ratio=1.64 hydroxyapatite was decomposed to $\alpha$-whitlockite above 120$0^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.165-166
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• 2008

$(Ba_{0.6},Sr_{0.3},Ca_{0.1})TiO_3$ powders, which were prepared by sol-gel method using a solution of Ba-acetate, Sr-acetate and Ca-acetate and Ti iso-propoxide, were mixed with organic vehicle and the BSCT thick films were fabricated by the screen-printing techniques on high purity alumina substrates. The structural and dielectirc properties were investigated for various $Pr_2O_3$ and $Y_2O_3$doping contents. As a result of thermal analysis of $(Ba_{0.6},Sr_{0.3},Ca_{0.1})TiO_3$ powders, the exothermic peak was observed at around $670^{\circ}C$ due to the formation of the polycrystalline perovskite phase. All BSCT thick films, sintered at $1420^{\circ}C$ for 2h, showed the typical XRD patterns of perovskite polycrystalline structure. The average grain size of the specimens decreased with amount of $Pr_2O_3$ and $Y_2O_3$ contents.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.11a
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• pp.167-167
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• 2008

The barium strontium calcium titanate powders were prepared by sol-gel method. Ferroelectric $(Ba_{0.54}Sr_{0.36}Ca_{0.1})TiO_3$(BSCT) thick films were fabricated by the screen-printing method on alumina substrate. And we investigated the structural and dielectric properties of BSCT thick films with the variation of sintering temperature. As a result of thermal analysis, BSCT polycrystalline perovskite phase was formed at around $660^{\circ}C$. The results of X-ray diffraction analysis were showed a cubic perovskite structure without presence of the second phase in all BSCT thick films. The average grain size and the thickness of the specimen sintered at $1450^{\circ}C$ were about 1.6 mm and 45 mm, respectively. The relative dielectric constant increased and the dielectric loss decreased with increasing the sintering temperature, the values of the BSCT thick films sintered at $1450^{\circ}C$ were 5641 and 0.4% at 1kHz, respectively.

• Journal of Korea Foundry Society
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• v.26 no.5
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• pp.211-216
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• 2006

The study for thixoextrusion process of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy was carried out with respect to reheating rate, isothermal holding temperature and time with an emphasis to the effect of homogenization on thixotropic micro-structures during the partial remelting, especially in the low liquid fraction ($f_L<0.2$). The liquid fraction and average grain size with respect to reheating profile such as reheating rate, isothermal holding temperature and time were almost uniform. It is considered very useful for thixoextrusion in terms of process control such as billet temperature control and actual extrusion time. Micro-structural controls of 7075, 7003 Al wrought alloys and AZ31 Mg wrought alloy before and after homogenization were available and thixotropic microstructures were obtained in both specimens.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1147-1161
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• 1995

When ceramic membrance was made from metal salt solution in place of metal akoxide solution, crack free and good adhesion to supporter was optimized for sol stability and good adhesion force. A starting sol was prepared from aluminum oxychloride aqueous solutjion in order to inhibit the grain growthof Al2O3 during heat treatment. The crack free dip coating can't be achieved in 1mol/ι zirconium oxychloride solution because of the high viscosity which interferes with the hydration copolymerization between Al3+ ion and Zr4+ ion. Thus Al2O3-ZrO2 sol stability and viscosity for dip coating was effective when 0.01 mol/ι zirconium oxychloride was added. The minimizing of crack and achieving better adhesion to the supporter wa obtained by microwave drying, surfactant addition and ultrasonic dip coating in wet atmosphere. The result seems to minimize the capillary force and improve the adhesive ability to supporter during the process. Where the average pore size of Al2O3-ZrO2 ultrafilter ceramic membrane measured 17 Å by the BET method and observed γ-Al2O3 phase with tetragonal zirconia after firing at 700℃.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.171-174
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• 2004

The surge characteristics of $Pr_6O_{11}$-based ZnO varistors consisting of $ZnO-Pr_6O_{11}-CoO-Cr_2O_3-Er_2O_3$ ceramics were investigated with sintering temperature in the range of $1335{\sim}1345^{\circ}C$. As the sintering temperature is raised, the average grain size was marked1y increased in the range of $9.67{\sim}14.07\;{\mu}m$ and the ceramic density was increased in the range of $5.46{\sim}5.59\;g/cm^3$. While, the nonlinear exponent was decreased in the range of 64.9~44.1 and the clamping voltage ratio was improved in the range of 1.99~2.08. The best varistor properties was obtained from the varistors sintered at $1335^{\circ}C$, exhibiting a maximum (64.9) in the nonlinear exponent and a minimum (1.99) in the clamping voltage ratio.

• Transactions on Electrical and Electronic Materials
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• v.18 no.6
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• pp.330-333
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• 2017

$Co_xMn_{3-x}O_4$ ($1.48{\leq}x{\leq}1.63$) ceramics were fabricated using the solid-state reaction method. Structural and electrical properties of specimens based on the composition ratio of Co were observed in order to investigate their applicability in NTC thermistors. All specimens showed a single spinel phase with a homogeneous tetragonal structure. The $Co_{1.57}Mn_{1.43}O_4$ specimen showed a maximum average grain size of approximately $6.47{\mu}m$. In all specimens, TCR properties displayed excellent characteristics of over $-4.2%/^{\circ}C$. The resistivity at 298 K and B-value of the $Co_{1.57}Mn_{1.43}O_4$ specimen were approximately $418{\Omega}-cm$ and 4300, respectively.