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Growth of high T{sub c} superconducting fibers using a miniaturized laser-heated float zone process. Annual progress report, October 15, 1989--November 5, 1990

Description: This report covers the research accomplished on the program entitled {open_quotes}Growth of High Tc Superconducting Fibers using a Miniaturized Laser-Heated Float Zone Process{close_quotes} during the 12.5 month period from Oct. 15, 1989 to Nov. 5, 1990. Research was done in four areas: phase relationships, preparation of starting materials, growth studies and the advanced fiber growth apparatus. The phase relationship studies built on the work published by Ono. Comparison studies with the well known compound Ca{sub 3}Al{sub 2}O{sub 6} confirmed that the Bi{sub 2+x}(Sr,Ca){sub 3-x}Cu{sub 2}O{sub y} is incongruently melting and that cuprous oxide, calcium oxide and (strontium, calcium) cuprate are the higher melting compounds which coexist with the melt and the superconducting phase. The preparation of the starting materials is crucial to the stable growth of the fibers. Non-uniform distribution of second phase particles, gaseous inclusions or porosity can lead to instabilities. A process was developed to ensure uniform starting materials. `Ibis process involves grinding the individual starting materials to a uniform size (44 {mu}m). The resulting powders are mixed and calcined three times with regrinding between each calcining step. The calcined powder is then cold pressed and sintered, reground, re-pressed and sintered. Ibis final material is then cut into bars for feed material for fiber growth. Growth rate studies showed a relationship between the growth rate and the regions of stability for single and multiphase fibers. This was traced to changes in the Bi and Cu levels in the melt related to changes in the growth rate. It was also shown that fluctuation in laser power lead to CaO inclusions in the fibers. The necessary components for the Advanced Fiber Growth Apparatus have been determined. Some of the components have been ordered and others are being designed.
Date: November 1, 1990
Creator: Feigelson, R.S.
Partner: UNT Libraries Government Documents Department

Growth of high T{sub c} superconducting fibers using a minaturized laser-heated float zone process. Annual progress report, January 1, 1993--December 31, 1993

Description: This report covers the research done on {open_quotes}Growth of High Tc Superconducting Fibers using a Miniaturized Laser-Heated Float Zone Process{close_quotes} during the 12 months from Jan. 1, 1993 until Dec. 31, 1993. The effort during this period were directed into two areas; the influence of growth conditions on the properties of the superconducting fibers and the construction of the advanced fiber growth station. In the first area of emphasis, studies were done on constitutional super cooling effect, the influence of processing parameters on Tc, the correlation between Tc and growth parameters and the mechanical properties of 2212 fibers. These studies showed that there are two types of interfacial breakdowns; one type that involves low temperature inclusions caused by excessive solute buildup and another involving high temperature inclusions which require two conditions to be met. These condition are: (1) significant compositional gradients in the melt and (2) an interface melt temperature near the peritectic decomposition temperature. Analysis of the experimental data lead to the hypothesis that fibers with the highest crystallinity are grown from SrO-rich 2212 melts. Evaluation of the constitutional supercooling responsible for the high temperature inclusions suggested that growth under these conditions was most vulnerable to disruption by HT inclusions. Tc increased with growth temperature for as-grown fibers. The concentration of SrO in the fibers had a parabolic relationship with temperature. The same parabolic relationship was observed between composition and Tc. The thermal history of 2212 crystals has been shown to influence their oxygen content which played a significant role in determining their Tc`s. Fiber heat treatment and the ambient gaseous atmosphere were found to dominate the Tc variations measured in this study.
Date: December 1, 1993
Creator: Feigelson, R.S.
Partner: UNT Libraries Government Documents Department

Growth of high T{sub c} superconducting fibers using a miniaturized laser-heated float zone process. Annual progress report, January 1, 1992--December 31, 1992

Description: This report covers the research done on {open_quotes}Growth of High Tc Superconducting Fibers using a Miniaturized Laser-Heated Float Zone Process{close_quotes} during the 12 months from Jan. 1, 1992 until Dec. 31, 1992. The major part of the work focused on phase relations and kinetics in the Bi{sub 2}O{sub 3}-SrO-CaO-CuO (BSCCO) system. By analyzing the crystal and melt composition, and the growth temperature of the float-zone samples, new data was obtained on the phase relationships. These results were shown to form a subset of solid solubility ranges reported by other investigators and was typical of the data available from other flux growth experiments. These experiments resulted in the development of a technique for the growth of long, single-phase 2212 samples. This was highly depended on starting material composition with Bi{sub 2.1}Sr{sub 1.8}Ca{sub 1.1}Cu{sub 2}O{sub y} being the most successful. Examination of the single phase 2212 growth interfaces was used to characterize the crystal/melt equilibrium conditions. These studies showed that 2212 crystal solidify from Bi{sub 2}O{sub 3}-rich and SrO-poor melts. Increasing melt concentrations of bismuth and cooper oxide increased the growth temperature. The sum of the bismuth and copper oxide in the crystals was invariant leading to the conclusion that the segregation of bismuth and copper oxide is interdependent. Work also proceeded on the new LHPG growth station.
Date: December 1, 1992
Creator: Feigelson, R.S.
Partner: UNT Libraries Government Documents Department

Improved techniques for the growth of optical-quality CdGeAs/sub 2/. Final report, December 1, 1976-December 31, 1977

Description: The ternary chalcopyrite compound CdGeAs/sub 2/ is one of the most efficient nonlinear infrared materials known. With transparency extending from 2.3 ..mu..m to 18 ..mu..m and a damage threshold exceeding 40 Mw/cm/sup 2/, it has a large number of potential applications, including doubling of the 10.6 ..mu..m CO/sub 2/ laser and continuous phase-matched mixing throughout its transparent region. It is also potentially suitable for certain acousto-optic applications consistent with its 4 2m space group symmetry. However, the growth of high optical quality, uncracked crystals of this material has been difficult. Polycrystallinity, cracking, and variable optical transparency were consistent problems. In this section we describe experiments carried out to eliminate (or control) polycrystallinity and cracking during the melt growth of this material.
Date: June 1, 1978
Creator: Feigelson, R.S. & Route, R.K.
Partner: UNT Libraries Government Documents Department

Growth of high phase-match temperature LiNbO/sub 3/ single crystals. Annual report for period ending March 15, 1978

Description: LiNbO/sub 3/ crystal with T/sub pm/ greater than or equal to 180/sup 0/C together with excellent phase matching characteristics and a high degree of optical homogeneity can be grown by the Czochralski technique with the following set of growth parameters: a melt composition of .54 Li/sub 2/O/.46 Nb/sub 2/O/sub 5/ doped with 1.0 mole % MgO; a growth rate of 2 mm/hr or less; positive axial and radial temperature gradients; and a crystal rotation rate of 50 rpm or higher to provide for a planar solid-liquid growth interface.
Date: September 1, 1978
Creator: Kway, W.L. & Feigelson, R.S.
Partner: UNT Libraries Government Documents Department

Growth of high T{sub c} superconducting fibers using a miniaturized laser-heated float zone process. Final technical report, January 15, 1989--December 31, 1994

Description: This report summarizes a four year program on the use of the laser-heated pedestral growth (LHPG) process for the preparation of long, flexible fibers of the high T{sub c} copper-oxide ceramic superconductors having wire-like morphology. The major question addressed was whether the LHPG method could produce high T{sub c} fibers of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (2212) in lengths long enough for use as superconducting wires. Cold-pressing and sintering methods were developed to prepare uniform, single phase ceramic feedstock. Phase equilibrium studies revealed the relationship between thermal gradients, interface shape and phases produced by the LHPG process during incongruent solidification. The highest critical current densities over measured in bulk samples of Bi-2212 material, 60,000 A/cm{sup 2} at 68K, were achieved in single crystal and/or highly grain-oriented fibers. The first ever flexible, multi-cm fibers ({le}100 {mu}m in diameter) were prepared. Fibers diameters were ultimately reduced to 25 {mu}m (1 cm in length), and we were able to grow them up to 14 cm in length (100 {mu}m diameter). These fibers could be bent in radii less than 5 cm, but max. growth rates of {approximately}10 mm/hr did not permit them to be grown long enough for prototype motor windings. Superconducting Bi-2212 grain-aligned ribbons were grown for the first time by the LHPG method using platinum guide wires.
Date: April 1, 1995
Creator: Feigelson, R.S.; Route, R.K. & DeMattei, R.C.
Partner: UNT Libraries Government Documents Department

Growth of high {Tc} superconducting fibers using a miniaturized laser-heated float zone process. Progress report, November 6, 1990--December 31, 1991

Description: This report summarizes the progress made on the project ``Growth of High {Tc} Superconducting Fibers Using a Miniaturized Laser-Heated Float Zone Process`` during the 14 month period from Nov. 6, 1990 to Dec. 31, 1991. The studies during this period focused primarily on phase diagram studies, phase relations in the calcium aluminate system and on Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub 8} (BSCCO). Some work was also done on the Advanced Fiber Growing Station. Because of the complicated phase relationships found in the incongruently melting BSCCO system, the incongruently melting CA{sub 3}Al{sub 2}O{sub 6} phase of the calcium oxide-aluminum oxide system was studied as a model material. The data obtained was in agreement with well known solidification theory. Fibers grown from calcium oxide rich sources contained calcium oxide nodules which transported from the melting source interface to the growth interface, while those grown from aluminum oxide rich sources contained continuous inclusions of a divorced eutectic. The melt compositions were also found to follow theoretical predictions. The agreement of this data with the phase diagram and solidification theory demonstrates that phase equilibrium information can be extracted from fiber growth experiments. BSCCO feed rods were made from 12 different compositions. Fibers were grown from these rods and the melts were abruptly quenched which preserves the as-grown 2212 fiber, a glassy frozen melt and the source. A future study of these sections will reveal the phase relationships that exist in the BSCCO system. Melt temperature gradients of 500--1,000 C/cm were measured near the interface in these experiments. During this reporting period, work continued on the mechanical components of the Advanced Fiber Growth Station.
Date: December 31, 1991
Creator: Feigelson, R.S.; Route, R.K. & DeMattei, R.C.
Partner: UNT Libraries Government Documents Department