• Journal of the Korean Crystal Growth and Crystal Technology
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• v.26 no.4
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• pp.135-138
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• 2016

It was observed that the single grain of crystallite growth behavior in AlN (Aluminum Nitride) single crystal growth by PVT (Physical Vapor Transport) method. The single grain of AlN was grown in sequent experiments and adjacent crystallites were joined together after small grain was grown. The sequential results of those grains observed by stereoscopic microscope were reported.

• Journal of the Korean Ceramic Society
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• v.49 no.1
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• pp.37-42
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• 2012

Mass transport near grain boundary in a magnetite bi-crystal has been estimated at 823 K by finite element method. Mass transport near grain boundary strongly depends on the diffusivities along grain boundary. If grain boundary diffusion has the same oxygen activity dependence as lattice diffusion, there is no mass transport between grains and grain boundary. On the other hand, mass transport between grains and grain boundary is observed in the case that grain boundary diffusion has different oxygen activity dependence.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.2
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• pp.122-127
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• 2000

Microstructural evolutions in ceria-stabilized zirconia (Ce-TZP) and alumina-dispersed Ce-TZP ceramics were investigated as functions of doping and annealing conditions. All of sintered specimens showed the relative density over 99 %. Sintered specimens had linear grain boundaries and normal grain shapes, but ceria-doped specimens had irregular grain shapes and nonlinear grain boundaries due to the diffusion-induced grain boundary migration during annealing at $1650^{\circ}C$ for 2 h. Mean grain boundary length of Ce-TZP with irregular grain shapes was higher than that of normal grain shapes, and was a value of 23pm at the maximum. Alumina particles dispersed in Ce-TZP inhibited the grain growth of zirconia particles. $Al_2O_3$Ce-TZP doped with ceria and annealed at $1650^{\circ}C$ for 2 h showed irregular grain shapes as well as small grain size. Added alumina particles showed the grain growth during sintering or annealing, and they changed the position from grain boundary to inside of the grains during the annealing. The specimens with normal grain shapes showed an intergranular fracture mode, whereas the specimens with irregular grain shapes showed a transgranular fracture mode during the crack propagation.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.11 no.2
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• pp.78-84
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• 2001

The binary forsterite($Mg_2SiO_4$)/spinel ($MgAl_2O_4$) system, a possible refractory for industrial applications, is investigated for their density and grain growth the same firing conditions as the each component material between $1400^{\circ}C$ and $1700^{\circ}C$ ($1650^{\circ}C$). The forsterite grain growth exponent is established to be equal to 5 for all compositions within this binary system. Generally; the spinel addition to forsterite inhibited the forsterite grain growth. The activation energies for the forsterite grain growth of the eight compositions(weight ratio of forsterite/spinel) within the binary system are determined to be: 952$\pm$79(95/5), 363$\pm$37(90/10), 219$\pm$21(80/20), 220$\pm$44(70/30), 112$\pm$16(50/50), 112$\pm$23(30/70), 198$\pm$26(10/90), and 121$\pm$12(5/95) KJ/mol. The more forsterite is contained within the binary system, the higher value the activation energy for forsterite grain growth. It is considered that the forsterite grain growth at the higher forsterite compositions are more inhibited by spinel than that of the lower forsterite compositions.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.29 no.6
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• pp.251-256
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• 2019

In the process of ZnO ceramic sintering at a temperature of 1385℃, higher than the normal sintering temperature, some grains were growth up to mm scale. When sintered at 1400℃ for 8 hours, the size of the grains that are not involved in the abnormal growth is as large as 30~40 ㎛, but the size of the abnormal grown grain reaches 1,000 ㎛, which is more than 10,000 times bigger in volume than the normal one within 8 hr growth. As a cause of rapid and abnormal grain growth, primary particle size distribution, compaction density variation within sample and doping of impurities could be considered. The primary particle size distribution could be considered main reason for abnormal grain growth but no solid evidence was obtained. Through the observation of the microstructure, it is presumed that the giant grains grow absorbing the neighbor grains through a grain rotation process.

• Progress in Superconductivity and Cryogenics
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• v.20 no.3
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• pp.5-10
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• 2018

This study presents that various grain boundary junctions are prepared by controlling the seed orientation combined with an artificial hole in a melt process REBCO bulk superconductor. Large grain YBCO superconductors have been fabricated with various grain boundary junctions that the angle between the grain boundary and the <001> axis of Y123 crystal is $0^{\circ}$, $30^{\circ}$ and $45^{\circ}$, respectively. The presence of the artificial hole is beneficial for the formation of clean grain boundary junction and single peak trapped magnetic field profiles have been obtained. Artificial hole makes two growth fronts meet at a point on a periphery of the artificial hole. The presence of artificial hole is not likely to affect on the distribution of Y211 particles. The newly formed <110> facet lines are explained by the formation of new Y123/liquid interface with (010) crystallographic plane.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.14 no.4
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• pp.151-154
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• 2004

Issues of ferroelectric high-density memories (>64 Mb) indispensable for upcoming ubiquitous era have been on the cell integration less than $0.1\;\mu\textrm{m}^2$ and reliabilities. Thus nanoscale control of microstructures of ferroelectric films with large switching polarization has been one of the issues to obtain the uniform electrical properties for realization of high-density memories. In this study the grain orientations and distributions of BT-based films by spin-on coatings were examined by FEG-SEM/EBSD. Ferroelectric domain characteristics by PFM were also performed to study the dependence of reliabilities on the grain orientations and distributions. It is believed that understandings of the nucleation and growth mechanisms of the a- or b-axis oriented films during the thermal processes such as RTA and furnace annealing affecting on grain orientation and uniformity could be possible based on our experimental results.

• Journal of the Korean Society for Precision Engineering
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• v.22 no.8 s.173
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• pp.84-91
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• 2005

The role of microstructure is quite significant in fretting of Ti-6Al-4V since its material properties depend strongly on crystallographic texture. In this study, we adopt crystal plasticity theory with a 2-D planar triple slip idealization to account fur microstructure effects such as grain orientation distribution, grain geometry, as well as $\alpha$ colony size. Crystal plasticity simulations suggest strong implications of microstructure effects at fretting contacts.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.2
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• pp.194-202
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• 1996

Transmission electron microscopy has been used to characterize the dislocation structure in hot-pressed titanium diboride. The thin foil samples were prepared by the conventional ion beam thinning technique and reveal the main features associated with the dislocations ; low-angle grain boundaries with dislocation arrays, high-angle grain boundaries with ledges/steps on the boundary planes. The ledges/steps on the grain boundaries were characterized as the origin of defect structures such as dislocation formation or crack propagation near grain boundaries. A fraction of the high angle grain boundaries contained periodic arrays of grain boundary dislocations. The Burger's vectors of the dislocations in the $TiB_{2}$specimens were determined.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.6 no.3
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• pp.431-438
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• 1996

Transmission electron microscopy has been used to investigate the microstructure of hot-pressed $TiB_{2}$. Thin foil specimens, prepared by conventional ion beam thinning, revealed many features which originated from the crystallographic anisotropy of hexagonal $TiB_{2}$. It was observed that in these specimens Fe-impurities are precipitated to form secondary Fe-rich phases at grain triple edges, in grain boundaries and sometimes in-grain. These Fe-rich precipitates were characterised by their coherence or semi-coherence to a favourably oriented grain at a grain triple edge or grain boundaries or to the matrix $TiB_{2}$ phase.