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Studies the effects of oxygen partial pressure PO2 during low temperature postheat treatments on the superconducting properties of silver-sheathed Bi2Sr2CaCu2Oy tapes. PO2's impact on the critical temperature Tc of the resulting tape; Characteristics of heat-treated tapes.

We present our studies of superconducting and microstructural properties of bulk MgB[sub 2]/Mg nano-composites and press-sintered MgB[sub 2]. TEM investigation revealed that the composites are very dense, consisting of nano-sized MgB[sub 2] grains connected by the well-defined clean grain boundaries (GB). Both amorphous and structural intact GB's were observed in the press-sintered samples. Magnetization and transport measurements showed that the composite carried over 1 MA/cm² critical current density (J[sub c]) at 5 K and self-field, while the pressed sintered MgB[sub 2] has J[sub c] ∼ 0.25 MA/cm² at 5 K and self-field. The origin of substantially higher J[sub c] found in the composites is mostly due to their nano-sized grains and clean grain boundaries. [ABSTRACT FROM AUTHOR]