Sol-Gel Processing of the Ti 2 Ca 1 Ba 2 Cu 2 O 8+X High Tc Superconducting Phase
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SOL-GEL PROCESSING OF THE TIzCaiBa2CuzOs+x HIGH Tc SUPERCONDUCTING PHASE M. R. Teepe, D. S. Kenzer, G. A. Moore, and G. Kordas Department of Materials Science and Engineering, Ceramics Division, and Science and Technology Center for Superconductivity, University of Illinois at Urbana-Champaign, 105 S. Goodwin, Urbana, IL 61801 Abstract An alkoxide Sol-Gel system was developed to produce bulk powders of the T12CalBa2Cu2O8+x high Tc superconducting phase. Methoxyethoxide and Cu(fl) ethoxide precursors were used for the formation of homogeneous sols. Solubility of the Cu(II) ethoxide was aided by using a 2-methoxyethanol/methyl ethyl ketone/toluene solvent system. The sols were characterized by small angle x-ray scattering (SAXS) and TEM. Powders were produced by rotary evaporation followed by thermal treatment in a closed container with thallium metal present at 900 oC for various calcination times. Powders were characterized by x-ray diffraction, resistivity and magnetic susceptibility measurements, and chemical analysis. Samples exhibited transition onsets between 100 and 110K depending upon the processing conditions.
Introduction Since the discovery 1-3 of superconductivity in the Tl-Ca-Ba-Cu-O system, much work has been done to determine the structure and properties of the superconducting phases in this system. These phases can be summarized as TlmCan_ 1Ba2CunOm+2(n+ 1)4 with n= 1, 2 and 3 and m=2 exhibiting Tc values of 90 K 1,2, 108 K 5, 125 K 5, respectively. The n-, m-, and Tc- values depend strongly on the synthesis conditions 5.6. Typical preparation conditions involve thorough mixing of T1203, CaO, BaO, and CuO in the desired ratios and firing at temperatures ranging from 880 to 950 oC in sealed containers 5-7. An alternative preparation method has been reported 8 which utilizes single phase CaBa2CuO4 as the Ca and Ba source to avoid the use of the corrosive and hygroscopic CaO and Bat materials. Previous work in this field has shown that superconducting powders and films can also be produced by the sol-gel technique . Using the spin or dip coating processes, for example, thin films can be produced which are uniform and highly oriented 9. Using the sol-gel process for these types of materials may therefore prove to be quite useful for a variety of applications. In this paper, we report a newly developed sol-gel route for the formation of the TI2CalBa2Cu2O 8 +x superconducting phase. Experimental Procedure Figure 1 outlines the procedure for sample preparation in the TI-Ca-Ba-Cu system by the sol-gel method. This process begins with the solubilization of the individual metal components to form alkoxide precursors. For this process, Cu(II) ethoxide was used and synthesized as follows: Cu(II)C12 + 4Li(C2H50) -----> Cu(II)(C2H50)2 + 2LiCl + 2Li(C2H50) The formation of the undesirable copper chloride ethoxide was avoided by using excess lithium ethoxide. 10 The copper ethoxide was separated from solution by means of a pressurized filtration device utilizing a 5 gtm PTFE membrane. Pure ethanol was forced throug
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