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Structures and superconductivity in perovskite bismuthate systems

Thesis/Dissertation ·
OSTI ID:7182140
Discovered in 1975, BaBi[sub 1[minus]x]Pb[sub x]O[sub 3] was one of the first high-T[sub c] oxide superconductors with a maximum T[sub c] of about 12 K. A controversy has persisted in the literature regarding the room-temperature structure of the entire solid solution. This has been especially true of the superconducting phase. Using high-resolution power neutron diffraction at the Intense Pulsed Neutron Source at Argonne National Laboratory, the room-temperature structures were determined for the region O [le] [times] [le] 0.8 as follows: monoclinic (I2/m) for 0 [le] [times] [le] 0.25, orthorhombic (Ibmm) for 0.25 < [times] < 0.7, and a two-phase region consisting of the orthorhombic (Ibmm) and a tetragonal (I4/mcm) phase for 0.7 [le] [times] [le] 0.8. High-temperature neutron diffraction on a sample with x = 0.8 revealed a first-order phase transition from tetragonal to orthorhombic as the sample is cooled below 425 K. Due to competing strains, however, the transition is incomplete, resulting in the observed two-phase behavior. Resistivity and susceptibility measurements indicate that only the metastable tetragonal phase is metallic and superconducting at low temperature. A comparison is made with the high-T[sub c] (30 K) Ba[sub 1[minus]y] K[sub y] BiO[sub 3].
Research Organization:
Illinois Inst. of Tech., Chicago, IL (United States)
OSTI ID:
7182140
Country of Publication:
United States
Language:
English