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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 5070-5072 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Films of YBa2Cu3O7−x prepared by laser ablation deposition show epitaxial growth on (100) SrTiO3 substrates with the c axis perpendicular to the plane of the film. With the magnetic field (H) parallel to the c axis, critical currents of up to 40 MA/cm2 from magnetization measurements are obtained. With H perpendicular to the c axis, various magnetization measurements with field cooling in 40 kOe indicated strong pinning effects with a calculated critical current density significantly higher than that observed in the parallel field configuration.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 4573-4577 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that voltage shifts in the hysteresis response of SrBi2Ta2O9 (SBT) thin-film capacitors can be induced using both thermal and optical methods. These voltage shifts are important since they can lead to imprint failure in ferroelectric memory devices. It is suggested that the voltage shifts in the hysteresis curve of SBT are caused by trapping of electronic charge carriers near the film/electrode interfaces, as has been previously reported for the Pb(Zr,Ti)O3 (PZT) system. In addition, a direct correlation is established between the magnitude and sign of remanent polarization (Pr) and the thermally induced voltage shifts (Vi), where Vi=αPr+β. It is also found that, unlike the PZT system, the thermally induced voltage shifts in SBT are smaller than those optically induced. One possible implication of this result is that the contribution of defect–dipole complexes to the voltage shifts in SBT is negligible. We suggest that the smaller contribution of defect-dipole complexes to the voltage shifts in SBT may be related to a smaller oxygen vacancy concentration in the perovskite sublattice of SBT as compared to that of PZT. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 6695-6702 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Switchable polarization can be suppressed in Pb(Zr,Ti)O3 thin films by optical, thermal, electrical, and reducing processes. The optical suppression effect occurs by biasing the ferroelectric near the switching threshold and illuminating the material with band gap light; the thermal suppression effect occurs by biasing the ferroelectric near the switching threshold and heating the material to ≈100 °C. The electrically induced suppression effect, known as electrical fatigue, occurs by subjecting the ferroelectric capacitor to repeated polarization reversals. We find that the suppressed polarization in these three cases can be restored to essentially its initial polarization value by creating electronic charge carriers in the ferroelectric. This strongly suggests that all three forms of degradation largely involve locking domains by electronic charge trapping at domain boundaries. The fourth form of polarization suppression, a reducing treatment, was obtained by annealing the crystallized PZT films at 400 °C in nitrogen. The suppressed polarization could not be restored by injecting electronic charge into the reduced films, indicating that the mechanism for polarization suppression is different. In this case, it appears as though ionic defects, such as oxygen vacancies, are responsible for locking the domains, and hence, suppressing the polarization. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 4305-4315 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pb(Zr,Ti)O3 and (Pb,La)(Zr,Ti)O3 thin films and bulk ceramics are shown to exhibit two distinct, but related types of photoinduced changes in their hysteresis behavior: (1) a photoinduced suppression of the switchable polarization and (2) a photoinduced voltage shift. Both effects give rise to stable and reproducible hysteresis changes and, thus, either could be the basis of an optical memory. Both phenomena can be explained by trapping of photogenerated charge at domain boundaries to minimize internal depolarizing fields. The space-charge field that causes the voltage-shift effect is primarily due to the migration and subsequent trapping of electrons. However, the thickness dependence of the voltage shift implies that the trapped charge is not confined to the interface. The voltage-shift kinetics exhibit a stretched-exponential dependence, whereas the polarization-suppression effect follows an exponential time dependence. However, both effects exhibit similar relaxation times. In addition, the relaxation time for the voltage-shift effect decreases with increasing light intensity according to a power-law relationship, τ∝I−n, where 0.67〈n〈0.75.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 9250-9257 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We show the alignment of defect dipoles along the direction of the spontaneous polarization in polycrystalline Pb(Zr,Ti)O3 and BaTiO3 ferroelectric ceramics using electron paramagnetic resonance (EPR). The alignment is demonstrated via orientation dependent paramagnetic centers in the polycrystalline materials and computer modeling of the EPR line shapes. It is shown that defect dipoles can become aligned by oxygen vacancy motion in the octahedron about a negatively charged center for the oxygen vacancy-related dipole complexes or by defect displacement and domain realignment in the lattice for isolated defect centers. We find that the alignment is not observed in nonferroelectric materials such as SrTiO3, and is destroyed in ferroelectric materials by heating above the Curie temperature. These observations suggest an interplay between distortion in the unit cell and the ability to align defect dipoles, as is the case more generally for ferroelectric dipole alignment. We also directly observe aligned intrinsic Ti and Pb ion displacements in the ferroelectric Pb(Zr,Ti)O3 perovskite unit cell. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 79 (1996), S. 1013-1016 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There have been numerous reports that Pb(ZrxTi1−x)O3 (PZT) thin-film capacitors with RuO2 electrodes and compositions near the morphotropic phase boundary exhibit minimal decrease in switched polarization with electric-field cycling. We show that the fatigue performance of RuO2//PZT//RuO2 capacitors strongly depends on PZT film composition. Specifically, we demonstrate that the rate of polarization fatigue increases with increasing Ti content for PZT thin films of tetragonal crystal symmetry deposited on RuO2 electrodes. As the Ti content of the PZT films increased, the film gain morphology changed from columnar to granular and the volume percent of a fluorite-type second phase decreased. These microstructural trends and the possibility that the electrode material acts as a sink for oxygen vacancies are discussed to explain the fatigue dependence on B-site cation ratio for PZT films with RuO2 electrodes. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 1682-1687 
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown that SrBi2Ta2O9 (SBT) thin films can be made to exhibit significant polarization fatigue by electric-field cycling under broad-band, optical illumination. Photoinduced fatigue is also observed for Pb(Zr,Ti)O3 (PZT) thin-film capacitors with (La,Sr)CoO3 (LSCO) electrodes. These results demonstrate that both the Pt/SBT/Pt and the LSCO/PZT/LSCO systems are susceptible to fatigue effects, which are attributed primarily to pinning of domain walls due to charge trapping. Capacitors that have been fatigued under illumination can be fully rejuvinated by applying a dc saturating bias with light or by electric-field cycling without light, which indicates an intrinsic, field-assisted recovery mechanism. We suggest that fatigue is essentially a competition between domain wall pinning and unpinning and that domain pinning is not necessarily absent in these nominally fatigue-free systems, but rather these systems are ones in which unpinning occurs at least as rapidly as any pinning. In both cases, the extent of photoinduced fatigue decreases with increased cycling voltage, indicating the relative importance of field-assisted unpinning. Finally, the observation of photoinduced fatigue implies that increased injection rates, potentially due to oxygen vacancy accumulation, may account for the electrode dependence on fatigue in PZT thin films.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 70 (1997), S. 2010-2012 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have examined the nature of the defects in BaTiO3 capacitors that have been subjected to an electric field at elevated temperatures (an accelerated aging process) using thermally stimulated current (TSC) and electron paramagnetic resonance measurements. The accelerated aging stress causes the ferroelectric capacitor to exhibit a reduction in its insulating resistance and a voltage offset in its polarization-voltage hysteresis loop. Following the accelerated aging treatment, the trapped charge estimates obtained from the TSC and the hysteresis measurements (as ascertained from the voltage offset) differ significantly and are attributed to either local charge compensation or uniform charge trapping within the dielectric. We also show that some of the trapped charge in ferroelectric materials is directly associated with the net polarization. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1681-1683 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: By systematically poling Pb(Zr,Ti)O3 capacitors to different extents, we observe a linear relationship between the remanent polarization and the magnitude of voltage offsets in the hysteresis curve. This result directly shows that the polarization is the impetus behind voltage shifts and, thus, imprint in ferroelectric capacitors. It is proposed that the increased polarization lowers the electrostatic potential well for the trapping of electrons thereby leading to greater voltage shifts. We also find that the remanent polarization and defect occupancy are temperature dependent which collectively impact the observed voltage offsets measured at elevated temperature. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2132-2134 
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first spatially resolved measurement of the critical transport current density of c-axis oriented epitaxial Y1Ba2Cu3O7 films on 〈100〉 SrTiO3 using low-temperature scanning electron microscopy (LTSEM). The local critical current density, imaged with a spatial resolution of ∼1 μm, has been found to vary considerably in these films. Possible reasons for the observed spatial inhomogeneities are surface imperfections of the substrate and precipitates in the film. The spatial inhomogeneity of the critical current density in epitaxial films might be a reason for differences in the temperature dependences of the critical current density obtained by magnetic and transport measurements.
    Type of Medium: Electronic Resource
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