The inherently weak mechanical properties associated with monolithic high-temperature superconductors (HTS) can be improved by introducing properly selected strong ceramic whiskers into the HTS materials. In this research, processing and superconducting properties of monolithic Pb-doped Bi-2223 (BPSCCO) and MgO whisker-reinforced BPSCCO HTS composite materials have been systematically studied. A solid-state processing method is successfully developed to fabricate the (MgO) w ͞BPSCCO composite. The HTS composite contains a dense and highly pure BPSCCO matrix phase with a preferred grain orientation, which is reinforced by MgO whiskers randomly oriented in the plane perpendicular to the hot-pressing direction. The HTS composite material is shown to exhibit excellent superconducting properties. For example, a transport J c measured at 77 K in a zero field has been obtained to exceed 5000 A͞cm 2 in a (MgO) w ͞BPSCCO composite with 10% MgO whiskers by volume. Relationships among solid-state processing variables, HTS phase development, and superconducting properties of the monolithic BPSCCO and the HTS composite are established in the paper.8

The phase diagram for the system NdI2O3‐P2O5 was constructed. Six intermediate compounds, having molar Nd2O3: P2O5 ratios of 3:1, 7:3, 1:1, 1:2, 1:3, and 1:5, were identified. The 3:1, 7:3, and 1:1 compounds are stable to at least 1500°C. The 1:2 compound decomposes to 1:1 and 1:3 at 730 ± 5°C. The 1:3 and 1:5 compounds melt congruently at 1280 ± 5° and 1055 ± 5°C, respectively. None of the neodymium phosphates show lower temperature limits of stability.

The inherently weak mechanical properties of bulk monolithic high-temperature superconductors (HTS) have been a concern. Properly selected reinforcements in fiber and whisker forms have been introduced to the HTS ceramics to improve their mechanical properties. In this paper, mechanical behavior of a MgO-whisker reinforced Pb-doped Bi-2223 (BPSCCO) HTS composite fabricated by a solid-state processing method is studied. The (MgO)w/BPSCCO HTS composite has been shown to exhibit excellent superconducting properties. Elastic properties, strengths, and notched fracture toughnesses of both the monolithic BPSCCO and the (MgO)w/BPSCCO HTS composite are investigated. Detailed mechanical properties are reported for the first time for the (MgO)w/BPSCCO HTS composite. Mechanisms of strengthening and toughening in the MgO-whisker-reinforced HTS composite are also discussed.

We report a systematic study of a series of single-phased LaiBa2Cu307-& samples where the oxygen content was determined by thermogravimetric analysis. The highest zero-resistance T, was 72 K, corresponding to 8 0.25. An increase in 8 reduced T, to 44 K, similar to the behavior reported for Y&Ba2Cu307-&. This is consistent with the idea that, as oxygen is taken away from the planes where Cu-0 chains exist, T, is reduced. For samples where the oxygen content was increased until 8 became negative, T, decreased to a value as low as 23 K, presumably due to increased La-Ba disorder. These samples with low T, and high oxygen content have apparent tetragonal x-ray spectra, suggesting that Cu-0 chain ordering has been further disrupted and that the oxygen occupancy on these planes has increased. Extensive experimental studies have been focused on the high-T, superconductor Y|BazCu307-s. Detailed neutron studies on this'2 compound as well as several structural studies on 1:2:3compounds with Y replaced by rare-earth elements,~~have associated the orthorhombic sequential structure with high zero-resistance T, 's near 90 K. The orthorhombicity is attributed to the ordering of oxygen vacancies in the copper planes between the Ba layers such that ordered Cu-0 chains remain. While the exact role of these Cu-0 chains is unclear, they are thought to be important to the high superconducting transition temperature either directly or through their interaction with the inner Cu-0 sheets. Recently, considerable attention has been focused on the compound LaiBa2Cu307s and its variations where different levels of lanthanum are doped into the barium sites. s '7 X-ray spectra on samples of the La|Ba2Cu307-s compound with low T, 's have been reported to appear tetragonal, although orthorhombic shoulderin~has been observed in samples with T, 's above 60 K. Further x-ray studies on samples of La|BazCu307-s with zero resistances as high as 80 K concluded that the samples with high T, 's were indeed orthorhombic. s7 This strengthens the idea that ordered Cu-0 chains play a very important role in these so-called 1:2:3 superconducting RiBa2Cu307-s (R is Y, La, and other rare-earth elements) materials, and that for these samples with T, 's approaching the 90-K plateau, an orthorhombic structure is required.The importance of the Cu-0 chains has been questioned by the observation that there exist certain LalBa2Cu3-07s samples that possess an apparent tetragonal structure but still become superconductors below 40 K. While several quenching studies on the Y|Ba2Cu307s compound have suggested an empirical relation between the orthorhombic distortion and T, (with the tetragonal phase being nonsuperconducting), a similar relationship has yet to be established in La|Ba2Cu307 s In thispa.per, we report a systematic study of the dependence of T, on the oxygen content (x) in La|Ba2Cu30q-s samples as measured by thermogravimetric analysis (TGA). The samples are predominantly single-phased with T, 's ranging from 23 to 72 K. Our highest zero-resistance transitio...

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