M.S. (Master of Science)
Department of Physics
In this thesis, the synthesis, characterization and properties of Ni and Zn substituted YBa[sub 2]Cu[sub 4]O[sub 8] high-T[sub c] superconducting single crystals and polycrystalline Sr^(57)FeO[sub x] samples will be presented. The unique Ni or Zn substituted millimeter size, flat single crystals of YBa[sub 2]Cu[sub 4]O[sub 8] (Y124) were grown at 1100 ?C and 600 bar of O[sub 2] pressure in a hot isostatic press furnace from polycrystalline starting materials BaCuO[sub 2], CuO, NiO/ZnO, and YBa[sub 2]Cu[sub 3]O[sub 7-?] (Y123). The starting contents for the substituted materials ranged from 1% to 5% for Ni, and from ly% to 20% for Zn. The final contents of Ni and Zn in the Y124 crystals were from 1.5% to 7% for Ni and 1% to 4% for Zn. It was difficult to obtain single crystals with high Zn doping since they frequently showed YBa[sub 2]Cu[sub 35]O[sub 75] impurity or mixed compositions of YBa[sub 2]Cu[sub 35]O[sub 75] and Y124. The superconducting transition temperatures, T[sub c], of these single crystals were measured with AC susceptibility and found to depend linearly on final Ni and Zn contents. In both cases, T[sub c] was suppressed to zero, which was not known for corresponding polycrystalline materials. Unlike in Y123, The Ni and Zn substitutions were found to suppress T[sub c] almost identically in Y124. The oxygen stoichiometric Sr^(57)FeO[sub 3.00] was successfully synthesized at 400 ?C and 300 bar in pure O[sub 2], followed by very slow cooling. By hydrogen reduction (20% H[sub 2] in Ar) and unique partial oxygen pressure annealings (0.2% or 12% O[sub 2] in Ar) with a thermogravimetric analyzer, the oxygen deficient Sr^(57)FeO[sub x] (x = 2.50, 2.74, 2.86 respectively) materials were made. X-ray and magnetic measurements showed agreement with the previous data and confirmed the high quality of the polycrystalline materials.
Chen, Zheng, "Synthesis, characterization, and property of Ni and Zn substituted YBa[sub 2]Cu[sub 4]O[sub 8] single crystals and Sr^(57)FeO[sub x] polycrystalline materials" (1996). Graduate Research Theses & Dissertations. 5192.
ix, 64 pages
Northern Illinois University
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