• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.21 no.5
• /
• pp.199-204
• /
• 2011

$(YSmNd)_{1.8}Ba_{2.4}Cu_{3.4}O_{7-x}$ [(YSN)1.8] high $T_c$ superconductor was directionally grown by zone melt growth process, in air atmosphere. In this study, optimum melting temperature and growth rate were $1100^{\circ}C$ and 3.5 mm/hr, respectively. The microstructure of well-textured (YSN)1.8 samples were examined by XRD, optical microscopy, TEM and SQUID magnetometer. The critical current density of these samples were measured by the direct transporting current method. In the observation using an optical microscopy, nonsuperconducting $(YSmNd)_2BaCuO_5$[(YSN)211] inclusions of (YSN)1.8 superconductor uniformly distributed within the superconducting (YSmNd)$Ba_2Cu_3O_x$[(YSN)123] matrix. The directionally melt-textured (YSN)1.8 superconductor showed an onset $T_c{\geq}90\;K$ and sharp superconducting transition. The transport $J_c$ values were 830 A and $3.93{\times}10^4$ (A/$cm^2$) at 77 K self-field, respectively.

• Journal of the Korean Crystal Growth and Crystal Technology
• /
• v.7 no.4
• /
• pp.610-618
• /
• 1997

$Al_2O_3$/Al composite was produced by the infiltration of molten Al Into $Al_2$O$_3$ preform at 900-$1200^{\circ}C$, The process was accelerated by spreading borosilicate glass powder onto the interface between Al powder compact and $Al_2O_3$ preform. Melt infiltration initialed after incubation period, and the growth of infiltration was observed to be linearly propotional with time. The major components of the composite are $Al_2O_3$ and Al with a trace of Si which is remained from borosilicate, the reaction accelerator. Relative density of the composite increased with the particle size of $Al_2O_3$ but decreased with infiltration temperature. As infiltration temperature increases from room to $950^{\circ}C$ higher strength and fracture toughness were obtained.

• Applied Chemistry for Engineering
• /
• v.8 no.3
• /
• pp.389-394
• /
• 1997

The distribution of impurity included in benzene layer crystal was explored in layer crystallization of cyclohexane and benzene mixtures. The influence of crystal growth rate on crystal purity was investigated. All experimental results for bezene-cyclohexane system obtained in layer crystallizer have been evaluated with the criterion of Wintermantel. The purity of crystal decreases with increasing degree of subcooling, decreasing feed concentration and increasing crystal growth rate. The crystal growth rate was a key parameter to determine the inclusion of impurity in crystals. The results obtained from runs performed at increasing crystallization time(i.e. crystal thickness) have clearly shown that migration of inclusions within crystal layer to the melt, leading to the removal of impurity occurs. The diffusion of impurity which takes place during the crystallization from the beginning, enhances a further purification of the crystal layer if that underwent a thermal gradient after growth of the layer crystal stops.

• 정보저장시스템학회:학술대회논문집
• /
• 2005.10a
• /
• pp.26-30
• /
• 2005

Stamper surface temperature is very critical in replicating the high density optical disc substrates using injection molding as the pit or land/groove patterns on the optical disc substrate have decreased due to the rapid increase of areal density. During the filling stage, the polymer melt in the vicinity of the stamper surfaces rapidly solidifies and the solidified layer generated during polymer filling greatly deteriorates transcribability and fluidity of polymer melt. To improve transcribability and fluidity of polymer melt, stamper surface temperature should be controlled such that the growth of the solidified layer is delayed during the filling stage. In this study, the effect of heating on replication process was simulated numerically. Then, an injection mold equipped with instant active heating system was designed and constructed to raise the stamper surface temperature over the glass transition temperature during filling stage of the injection molding. Also, the closed loop controller using the Kalman filter and the linear quadratic Gaussian regulator was designed. As a result, the stamper surface temperature was controlled according to the desired reference stamper surface temperature.

• Transactions of the Society of Information Storage Systems
• /
• v.2 no.2
• /
• pp.100-104
• /
• 2006

Stamper surface temperature is very critical in replicating the high density optical disc substrates using injection molding as the pit or land/groove patterns on the optical disc substrate have decreased due to the rapid increase of areal density. During the filling stage, the polymer melt in the vicinity of the stamper surfaces rapidly solidifies and the solidified layer generated during polymer filling greatly deteriorates transcribability and fluidity of polymer melt. To improve transcribability and fluidity of polymer melt, stamper surface temperature should be controlled such that the growth of the solidified layer is delayed during the filling stage. In this study, the effect of heating on replication process was simulated numerically. Then, an injection mold equipped with instant active heating system was designed and constructed to raise the stamper surface temperature over the glass transition temperature during filling stage of the injection molding. Also, the closed loop controller using the Kalman filter and the linear quadratic Gaussian regulator was designed. As a result. the stamper surface temperature was controlled according to the desired reference stamper surface temperature.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1997.04a
• /
• pp.225-228
• /
• 1997

YBa$_2$Cu$_3$O$_{x}$ samples with different amounts of $Y_2$BaCuO$_{5}$ were prepared by MPMG (Melt Powder Melt Growth) method. The effects on the size of initial particles and Ag addition for $Y_2$BaCuO$_{5}$ distribution in YBa$_2$Cu$_3$O$_{x}$ were invesgated. The samples prepared by the melting process usually have large grains up to several ㎣ and precipitates of $Y_2$BaCuO$_{5}$. The distribution of the $Y_2$BaCuO$_{5}$ particles in the samples depends on the size of initial particles and the amounts of Ag addition.Ag addition.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.04a
• /
• pp.14-16
• /
• 2002

Melting and re-solidification nature of $SmBa_2Cu_3O_{7-y}$ (Sm123) grains in Ba-Cu-O (Ba:Cu=3:5) liquid containing 0.7 at.% yttrium were investigated at the temperature lower than its melt point. When Sm123 grains/liquid powder compacts were heated to a temperature between two melting points of Ba-Cu-O liquid ($1000^{\circ}C$) and a Sm123 phase ($1060^{\circ}C$) and held at this temperature for appropriate time, Sm123 grains melted partly in the liquid that was formed by melting of the liquid-forming powder. During subsequent slow cooling, (Sm,Y)$Ba_2Cu_3O_{7-y}$ solidified at the outer parts of the unmelted Sm12 grains, which is distinguished from the core regions by lower $Sm_2BaCuO_5$ (211) density.

• Proceedings of the Korea Association of Crystal Growth Conference
• /
• 1996.06a
• /
• pp.258-292
• /
• 1996

In the last year great interest appears to YBCO thin films preparation on different substrate materials. Preparation of epitaxial film is a very difficult problem. There are many requirements to substrate materials that must be fullfilled. Main problems are lattice mismatch (misfit) and similarity of structure. From paper [1] or follows that difference in interatomic distances and angles of substrate and film is mire important problem than similarity of structure. In this work we present interatomic distances and angle relations between substrate materials belonging to ABCO4 group (where A-Sr or Ca, B-rare earth element, C-Al or Ga) of different orientations and YBCO thin films. There are many materials used as substrates for HTsC thin films. ABCO4 group of compounds is characterized by small dielectric constants (it is necessary for microwave applications of HTsC films), absence of twins and small misfit [2]. There most interesting compounds CaNdAlO4, SrLaAlO4 and SrLaGaO4 were investigated. All these compounds are of pseudo-perovskite structure with space group 14/mmm. This structure is very similar to structure of YBCO. SLG substrate has the lowest misfit (0.3%) and dielectric constant. For preparation of then films of substrates of this group of compound plane of <100> orientation are mainly used. Good quality films of <001> orientations are obtained [3]. In this case not only a-a misfit play role, but c-3b misfit is very important too. Sometimes, for preparation of thin films substrates of <001> and <110> orientations were manufactured [3]. Different misfits for different YBCO faces have been analyzed. It has been found that the mismatching factor for (100) face is very similar to that for (001) face so there is possibility of preparation of thin films on both orientations. SrLaAlO4(SLA) and SrLaGaO4(SLG) crystals of general formula ABCO4 have been grown by the Czochralski method. The quality of SLA and SLG crystals strongly depends on axial gradient of temperature and growth and rotation rates. High quality crystals were obtained at axial gradient of temperature near crystal-melt interface lower than 50℃/cm, growth rate 1-3 mm/h and the rotation rate changing from 10-20pm[4]. Strong anisotropy in morphology of SLA and SLG single crystals grown by the Czochralski method is clearly visible. On the basics of our considerations for ABCO4 type of the tetragonal crystals there can appear {001}, {101}, and {110} faces for ionic type model [5]. Morphology of these crystals depend on ionic-covalent character of bonding and crystal growth parameters. Point defects are observed in crystals and they are reflected in color changes (colorless, yellow, green). Point defects are detected in directions perpendicular to oxide planes and are connected with instability of oxygen position in lattice. To investigate facets formations crystals were doped with Cr3+, Er3+, Pr3+, Ba2+. Chromium greater size ion which is substituted for Al3+ clearly induces faceting. There appear easy {110} faces and SLA crystals crack even then the amount of Cr is below 0.3at.% SLG single crystals are not so sensitive to the content of chromium ions. It was also found that if {110} face appears at the beginning of growth process the crystal changes its color on the plane {110} but it happens only on the shoulder part. The projection of {110} face has a great amount of oxygen positions which can be easy defected. Pure and doped SLA and SLG crystals measured by EPR in the<110> direction show more intensive lines than in other directions which allows to suggest that the amount of oxygen defects on the {110} plane is higher. In order to find the origin of colors and their relation with the crystal stability, a set of SLA and SLG crystals were investigated using optical spectroscopy. The colored samples exhibit an absorption band stretching from the UV absorption edge of the crystal, from about 240 nm to about 550 m. In the case of colorless sample, the absorption spectrum consists of a relatively weak band in the UV region. The spectral position and intensities of absorption bands of SLA are typical for imperfection similar to color centers which may be created in most of oxide crystals by UV and X-radiation. It is pointed out that crystal growth process of polycomponent oxide crystals by Czochralski method depends on the preparation of melt and its stoichiometry, orientation of seed, gradient of temperature at crystal-melt interface, parameters of growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth (rotation and pulling rate) and control of red-ox atmosphere during seeding and growth. Growth parameters have an influence on the morphology of crystal-melt interface, type and concentration of defects.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.20 no.3
• /
• pp.988-1004
• /
• 1996

The characteristics of flow and oxygen concentration are numerically studied in Czochralski 8" silicon crystal growing process considering radiative heat transfer. The analysis of net radiative heat flux on all relevant surfaces shows growing crystal affects the heater power. Furthermore, the variation of the radiative heat flux along the crystal surface in the growing direction is confirmed and should be a cause of thermal stress and defect of the crystal. The calculated distributions of temperature and, heat flux along the wall boundaries including melt/crystal interface, free surface and crucible wall indicate that the frequently used assumption of the thermal boundary conditions of insulated crucible bottom and constant temperature at crucible side wall is not suitable to meet the real physical boundary conditions. It is necessary, therefore, to calculate radiative heat transfer simultaneously with the melt flow in order to simulate the real CZ crystal growth. If only natural convection is considered, the oxygen concentration on the melt/crystal interface decreases and becomes uniform by the application of a cusp magnetic filed. The heater power needed also increases with increasing the magnetic field. For the case of counter rotation of the crystal and crucible, the magnetic field suppresses azimutal flow produced by the crucible rotation, which results in the higher oxygen concentration near the interface.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.15 no.3
• /
• pp.269-274
• /
• 2002

(Sm/Y)-Ba-Cu-O system high Tc composite superconductors with/without $CeO_2$ additive were directionally grown by zone-melting process, haying large temperature gradient, In air atmosphere. Cylindrical green rods of $({Sm/y})_{1.8}Ba_{2.4}Cu_{3.4}O_x$ [(Sm/Y)1.8] composite oxides by cold isostatic pressing(CIP) method using rubber mold were fabricated. The microstructure and superconducting properties were investigated by XRD, SEM, TEM and SQUID magnetometer. The size of nonsuperconducting $({Sm/y})_2BaCuO_5$ inclusions of the melt-textured (Sm/Y)1.8 sample with CeO$_2$ additive were remarkably reduced and uniformly distributed within the superconducting (Sm/Y)1.8 matrix. Both samples, with/without $CeO_2$ additive, showed an onset Tc $\geq$ 90 K and sharp superconducting transition. The critical current density Jc value of the $CeO_2$ addictive were $1{\times}10^5A/\textrm{cm}^2$ in 77 K, 0 Tesla.