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10 Aug 1987

Volume 51, Issue 6, pp. 381-465

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Fracture toughness measurements of YBa2Cu3Ox single crystals

Robert F. Cook, Timothy R. Dinger, and David R. Clarke

Appl. Phys. Lett. 51, 454 (1987); http://dx.doi.org/10.1063/1.98420 (3 pages) | Cited 84 times

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We report fracture toughness measurements on single crystals of YBa2Cu3Ox, the phase responsible for superconductivity above liquid‐nitrogen temperatures. Indentation crack length measurements on the (010) orthorhombic crystal growth faces revealed the (100) and (001) planes as preferred fracture planes. The toughness of these planes is Kc=1.1±0.3 MPa m1/2, and the hardness H=8.7±2.4 GPa. The observed growth of both radial and lateral cracks in ambient air suggests that these crystals are susceptible to moisture‐enhanced nonequilibrium crack propagation.
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62.20.M- Structural failure of materials
81.40.Np Fatigue, corrosion fatigue, embrittlement, cracking, fracture, and failure

New phases in the superconducting Y:Ba:Cu:O system

D. J. Eaglesham, C. J. Humphreys, N. McN. Alford, W. J. Clegg, M. A. Harmer, and J. D. Birchall

Appl. Phys. Lett. 51, 457 (1987); http://dx.doi.org/10.1063/1.98421 (3 pages) | Cited 27 times

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An electron diffraction and microscopy study is presented of a variety of phases in the Y:Ba:Cu:O system in which superconductivity occurs. The superconducting phase is demonstrated by convergent beam electron diffraction to be centrosymmetric with space group Pmmm, in contrast to a previous determination of Pmm2. This discrepancy arises from local symmetry‐breaking defects. In addition to this phase and a cubic BaCuO2 phase, we characterize two other phases. One is the Y‐rich orthorhombic phase: Pnma with a=13.5 Å, b=6.3 Å, and c=7.6 Å. The second occurs by a phase transition of the superconducting Pmmm phase to P4/mmm with a=3.85 Å, c=11.7 Å. The superconducting phase may now be described as either an ordered array of oxygen vacancies in the perovskite structure, or an ordered array of oxygen interstitials in the new tetragonal phase, which may explain how the material can lose oxygen reversibly.
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61.66.Fn Inorganic compounds
74.70.Ad Metals; alloys and binary compounds (including A15, MgB2, etc.)
74.70.-b Superconducting materials other than cuprates
64.70.K- Solid-solid transitions

Critical current of Y1Ba2Cu3O7 in strong applied fields

Uri Dai, Guy Deutscher, and Ralph Rosenbaum

Appl. Phys. Lett. 51, 460 (1987); http://dx.doi.org/10.1063/1.98422 (3 pages) | Cited 9 times

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Critical currents of the new high‐temperature superconductor Y1Ba2Cu3O7 have been measured in applied fields of up to 7 T and for temperatures down to 70 K. We find that the critical current is drastically reduced by the application of magnetic fields much smaller than the upper critical field of the samples, Hc2. This anomalous behavior might be due to very weak pinning, or to a very strong anisotropy of Hc2. Hc2 is found to follow a linear temperature dependence that however extrapolates to a critical temperature higher than that measured directly. This might result from the existence of a percolative structure, or from the presence of a small volume fraction of high critical temperature, high critical field regions.
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74.25.Op Mixed states, critical fields, and surface sheaths
74.70.-b Superconducting materials other than cuprates

Oxide trapping under spatially variable oxide electric field in the metal‐oxide‐silicon structure

E. Avni and J. Shappir

Appl. Phys. Lett. 51, 463 (1987); http://dx.doi.org/10.1063/1.98423 (3 pages) | Cited 13 times

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An improved trapping‐detrapping model is presented describing the effect of electron injection into the oxide of metal‐oxide‐silicon devices. The model covers both hot‐electron and tunneling injection. It takes into account the spatial variation of the oxide electric field due to the trapped charge as well as the effect of this variation on the trapping‐detrapping processes. The calculated results agree well with previously reported experimental results such as the field‐dependent steady‐state flatband voltage and the trapped charge centroid.
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73.40.Qv Metal-insulator-semiconductor structures (including semiconductor-to-insulator)
73.50.Gr Charge carriers: generation, recombination, lifetime, trapping, mean free paths
85.30.Mn Junction breakdown and tunneling devices (including resonance tunneling devices)
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