Hai-Woong Park

Microstructure of melt-textured Y - Ba - Cu - O oxides with addition and the formation mechanism of the Ba - Cu - O platelet structure

Melt-textured (Y123) containing fine particles of (Y211) has been prepared from Y123/Y211 powder that was attrition milled with 1 wt% addition, and the microstructure has been examined. Fine and spherical Y211 particles (less than 1 m in size) are found to be homogeneously dispersed within the melt-textured Y123 domain. Many dislocations are observed to be formed around the trapped Y211 and the inclusions, which were formed as a result of addition and introduction from the jar and ball used for attrition milling. CuO stacking faults were also observed around the trapped Y211; these were initiated at the Y123/Y211 interface and extended into the Y123 matrix. Each stacking fault has a lenticular shape, with a width of a few tens of nanometres and a length of a few hundred nanometres, and the faults developed along the [100] and [010] directions of the Y123. The formation mechanism of the stacking fault was discussed together with the formation of the platelet structure (the elongated Ba - Cu - O phase) on the basis of an oxygenation-induced decomposition of the Y123 phase. It is concluded that the prolonged oxygenation heat treatment producing the tetragonal-to-orthorhombic phase transformation is responsible for the formation of the platelet structure and possibly for the formation of the stacking faults.

New method of producing fine Y2BaCuO5 in the melt-textured Y-Ba-Cu-O system: attrition milling of YBa2Cu3Oy-Y2BaCuO5 powder and CeO2 addition prior to melting

A new process yielding fine Y211 particles in melt-textured Y-Ba-Cu-O was developed by combining attrition milling of Y123-Y211 powder and CeO2 addition prior to the partial melting. Beneficial points of the attrition milling are as follows: (1) it allows uniform distribution of the Y211 refiner (CeO2) in the Y123-Y211 powder mixture, (2) it produces nanocrystalline Y123 powder with large surface area per unit volume which increases the possibility of Y211 nucleation during incongruent melting and (3) it controls the number and the size of Y211 particles preformed at the calcination/sintering stage from the off-stoichiometric powder of Y1.8 composition. The Y211 particles of the melt-textured Y123 sample which was prepared from the attrition-milled powder were of submicrometre scale and their distribution was quite uniform. The critical current density (Jc) at 77 K of the melt-textured Y1.8 sample containing fine Y211 (less than 1 mu m) was 2.0*104 A cm-2 and 1.16*104 A cm-2 at 1 T and 2 T, respectively, which is twice the Jc of 1.1*104 A cm-2 (at 1 T) and 0.56*104 A cm-2 (at 2 T) of the Y1.8 sample containing coarse Y211 ( approximately 5 mu m in average size).

Femtosecond laser treatment of 316L improves its surface nanoroughness and carbon content and promotes osseointegration: An in vitro evaluation.

Cell-material surface interaction plays a critical role in osseointegration of prosthetic implants used in orthopedic surgeries and dentistry. Different technical approaches exist to improve surface properties of such implants either by coating or by modification of their topography. Femtosecond laser treatment was used in this study to generate microspotted lines separated by 75, 125, or 175μm wide nanostructured interlines on stainless steel (316L) plates. The hydrophobicity and carbon content of the metallic surface were improved simultaneously through this method. In vitro testing of the laser treated plates revealed a significant improvement in adhesion of human endothelial cells and human bone marrow mesenchymal stem cells (hBM MSCs), the cells involved in microvessel and bone formation, respectively, and a significant decrease in fibroblast adhesion, which is implicated in osteolysis and aseptic loosening of prostheses. The hBM MSCs showed an increased bone formation rate on the laser treated plates under osteogenic conditions; the highest mineral deposition was obtained on the surface with 125μm interline distance (292±18mg/cm(2) vs. 228±43mg/cm(2) on untreated surface). Further in vivo testing of these laser treated surfaces in the native prosthetic implant niche would give a real insight into their effectiveness in improving osseointegration and their potential use in clinical applications.

Texture and surface analysis of NiO buffer deposited on biaxially textured Ni tapes by a MOCVD method

NiO buffer layers for YBCO coated conductors were deposited on textured Ni substrates by a metal-organic chemical vapor deposition(MOCVD) method. Processing variables were the oxygen partial pressure and substrate temperature. The degree of texture and the surface roughness of the deposited NiO surface were analyzed by X-ray pole figure, atomic force microscopy (AFM), and scanning electron microscope (SEM). The (200) textured NiO layer was formed at 450 /spl sim/ 470 /spl deg/C and oxygen partial pressure of 1.67 Torr. Out-of-plane(/spl omega/-scan) and in-plane(/spl Phi/-scan) texture were 10.34/spl deg/ and 10.00/spl deg/, respectively. The surface roughness estimated by atomic force microscopy was in the range of 3.1 /spl sim/ 4.6 nm which was much smoother than that prepared by an oxidation method. We discuss the development of the (200) texture in the MOCVD-NiO films in terms of processing variables.

Size reduction of Nd4Ba2Cu2O10 second phase particles in NdBa2Cu3O7 − y melt-textured at reduced oxygen partial pressure

Abstract Melt-textured NdBa 2 Cu 3 O 7 − y (Nd123) superconductor containing fine Nd 4 Ba 2 Cu 2 O 10 (Nd422) particles was prepared by using Nd 1.8 Ba 2.4 Cu 3.4 O x (Nd1.8) powder attrition-milled with 1 wt% CeO 2 addition. The effect of the CeO 2 addition on the size reduction of the Nd422 was remarkable and similar as those observed for Y 2 BaCuO 5 (Y211)/Sm 2 BaCuO 5 (Sm211) in the Y-Ba-Cu-O/Sm-Ba-CuO system. The Nd422 particles were finely dispersed within the melt-textured Nd123 matrix with a narrow size distribution of a few microns. Superconducting transition temperatures ( T c ) of the Nd123 and the Nd1.8 samples melt-textured in an oxygen partial pressure of P ( O 2 ) = 0.001 atm were as high as 95 K.

Control of Y2BaCuO5 morphology in melt-textured YBaCuO oxides with PtO2·H2O addition

Abstract The influence of precursor composition (YBa 2 Cu 3 O x and Y 1.6 Ba 2.3 Cu 3.3 O x ) and a procedure of PtO 2 ·H 2 O addition on Y 2 BaCuO 5 morphology was investigated in melt-textured YBaCuO oxides. It is found that the 2-1-1 morphology sensitively depends not only on the composition of the starting material but also on the adding procedure of PtO 2 ·H 2 O powder. In YBa 2 Cu 3 O x , coarse/plate-like Y 2 BaCuO 5 particles are produced, while fine/equiaxed 2-1-1 particles are produced in Y 1.6 Ba 2.3 Cu 3.3 O x . On the other hand, needle-like 2-1-1 particles are produced when 1 wt.% PtO 2 ·H 2 O was added to Y 2 O 3 BaCO 3 CuO while granular 2-1-1 particles are produced when PtO 2 ·H 2 O was added to YBa 2 Cu 3 O x −Y 2 BaCuO 5 powder. Y 2 BaCuO 5 morphologies developed from precursors with/without PtO 2 ·H 2 O addition are discussed on the basis of the growth behavior of Y 2 BaCuO 5 particles at the reaction stages (the solid-state, incongruent melting and peritectic reaction) of melt-texture processing.

Deposition of CeO/sub 2/ buffer layers for YBCO coated conductors on biaxially textured Ni substrates by MOCVD technique

CeO/sub 2/ buffer layers for YBa/sub 2/Cu/sub 3/O/sub 7/(YBCO) coated conductors were deposited on biaxially textured Ni substrates by metalorganic chemical vapor deposition (MOCVD) method. The variables were the oxygen partial pressure (P/sub O2/), deposition temperature and time. The [200] texture of CeO/sub 2/ was formed at T = 500 /spl deg/C - 520 /spl deg/C, t = 3 - 15 min and P/sub O2/ = 2.30 torr, while the [111] and [200] texture were competitively formed at other condition. The surface roughness of CeO/sub 2/ films was as good as 5 - 15 nm up to 500 /spl deg/C, while it rapidly increased as a result of grain growth of the CeO/sub 2/ at T /spl ges/ 520 /spl deg/C. The surface roughness of the CeO/sub 2/ films also increased as the deposition time increased. The growth rate of the CeO/sub 2/ films at T = 520 /spl deg/C and P/sub O2/ = 2.30 torr was 200 nm/min, which is much higher than those prepared by other physical deposition methods.

Synthesis of YBa2Cu3Oy superconductors via attrition-milled intermediate oxide precursor containing BaCuO2.5

YBa2Cu3Oy (Y123) phase was synthesized from the oxide precursor containing BaCuO2.5 in two distinct processes. in the first stage, a suitable amount of metallic Y, metallic Cu and barium nitrate (Ba(NO3)2) were mixed via attrition milling for 20 h. After 20 h of milling, the particle size of the powder was in the range of 0.05–0.2 μm. On subsequent heat treatment of the milled powder at 600°C for 5h with continuous argon flow, the intermediate precursor (IP) was synthesized. The IP contained BaCuO2.5, Y2O3 and CuO and the overall composition of the IP was Y:Ba:Cu:O=1:2:3:7.4. The oxygen content of the IP was higher than that of the corresponding orthorhombic Y123 superconductor. In the second stage, the synthesized IP was converted to the superconducting Y123 phase with heat treatment at 900–1020°C in air without any additional low temperature oxygenation process. A DTA experiment at 20°C/min in air and a series of rapid heat, soak, and quench experiments showed that the BaCuO2.5 constituent of the precursor decomposed at 838°C, which is higher than that of pure BaCuO2.5 (760°C). The results of the TGA experiments suggested that the heating rate had a strong influence on the decomposition temperature of the BaCuO2.5 of the IP. At a heating rate of>50°C/min, the BaCuO2.5 did not decompose completely during heating to 1020°C and form orthorhombic YBa2Cu3O7-x.

Three-dimensional shape of the Y2BaCuO5 pattern in melt-textured Y–Ba–Cu–O oxide

AbstractCrystallographic orientations of the Y211 tracks that were trapped within the melt-textured Y123 domains were determined from the orientation relationship among the Y211 pattern,