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With the increasing importance of electrified transport, the need for high energy density storage is also increasing. Possible candidates include Li-O2 batteries, which are the subject of rapidly increasing focus worldwide despite being in their infancy of understanding. This excitement owes to the high energy density of Li-O2 (up to 2-3 kWh kg−1), theoretically much higher compared to that of other rechargeable systems, and the open 'semi-fuel' cell battery configuration that uses oxygen as the positive electrode material. To bring Li-O2 batteries closer to reality as viable energy storage devices, and to attain suitable power delivery, understanding of the underlying chemistry is essential. Several concepts have been proposed in the last year to account for the function and target future design of Li-O2 batteries and these are reviewed. An overview is given of the efforts to understand oxygen reduction/evolution and capacity limitations in these systems, and of electrode and electrolyte materials that are suitable for non-aqueous and hybrid (nonaqueous/aqueous) cells. [ABSTRACT FROM AUTHOR]

Here we report the observation of electron delocalization in nano-dimension xLiFePO4:(1 − x)FePO4(x= 0.5) using high temperature, static, 31P solid state NMR. The 31P paramagnetic shift in this material shows extreme sensitivity to the oxidation state of the Fe center. At room temperature two distinct 31P resonances arising from FePO4and LiFePO4are observed at 5800 ppm and 3800 ppm, respectively. At temperatures near 400 °C these resonances coalesce into a single narrowed peak centered around 3200 ppm caused by the averaging of the electronic environments at the phosphate centers, resulting from the delocalization of the electrons among the iron centers. 7Li MAS NMR spectra of nanometre sized xLiFePO4:(1 − x)FePO4(x= 0.5) particles at ambient temperature reveal evidence of Li residing at the phase interface between the LiFePO4and FePO4domains. Moreover, a new broad resonance is resolved at 65 ppm, and is attributed to Li adjacent to the anti-site Fe defect. This information is considered in light of the 7Li MAS spectrum of LiMnPO4, which despite being iso-structural with LiFePO4yields a remarkably different 7Li MAS spectrum due to the different electronic states of the paramagnetic centers. For LiMnPO4the higher 7Li MAS paramagnetic shift (65 ppm) and narrowed isotropic resonance (FWHM 500 Hz) is attributed to an additional unpaired electron in the t2gorbital as compared to LiFePO4which has δiso= −11 ppm and a FWHM = 9500 Hz. Only the delithiated phase FePO4is iso-electronic and iso-structural with LiMnPO4. This similarity is readily observed in the 7Li MAS spectrum of xLiFePO4:(1 − x)FePO4(x= 0.5) where Li sitting near Fe in the 3+ oxidation state takes on spectral features reminiscent of LiMnPO4. Overall, these spectral features allow for better understanding of the chemical and electrochemical (de)lithiation mechanisms of LiFePO4and the Li-environments generated upon cycling. [ABSTRACT FROM AUTHOR]

The polycrystalline structure of pulsed-laser deposited Y-Ba-Cu-O thin films was studied using transmission electron microscopy. Many grains of the superconducting films on (001) SrTiO3 substrates had the c axis normal to the surface, while grains on (110) facets had their c axis oriented preferentially along the interface. Observation of an amorphous layer of thickness ∼6 nm at some oriented grain-substrate interfaces suggests that the amorphous layer is formed subsequent to the formation of the crystalline structures. Surface ridges were found to facilitate the formation of triple points where the grain boundaries between nonepitaxial grains were pinned. [ABSTRACT FROM AUTHOR]

Various orientations of YBa2Cu3O7-x grains in polycrystalline films prepared on (001)MgO substrates by in situ laser deposition were determined using electron diffraction. Eight different types of in-plane orientations have been observed. These orientations agree well with the prediction of a simplified theory of near coincidence site lattice between YBa2Cu3O7-x and MgO. The YBa2Cu3O7-x grains were found to have a high probability of forming low angle or low Σ boundaries among themselves. These grain boundaries are of low energy and should exhibit a high connectivity of Cu-O-Cu chains. Therefore, YBa2Cu3O7-x thin films on MgO can attain a Tc of ∼90 K and a Jc of ∼106 A/cm2 at 77 K. [ABSTRACT FROM AUTHOR]

We have performed intra- and extra-cavity microwave frequency (1–100 GHz) measurements on high quality Y1Ba2Cu3O7-x superconducting thin films on (100) LaAlO3 substrates. The ∼0.3 μm thin films fabricated by the pulsed laser deposition technique exhibit superconducting transition temperatures >90 K, as determined by resistivity and ac susceptibility measurements, and critical current densities of 5×106 A/cm2 at 77 K. Moreover, ion beam channeling minimum yields of ∼3% were measured, indicating the extremely high crystalline quality of films grown on the LaAlO3 substrate. Microwave surface resistance values at 77 K for these films are found to be more than one to two orders of magnitude lower than for copper at 77 K for almost the entire frequency range explored. We postulate that the reason we observe such low surface resistances in these films is the virtual absence of grain and phase boundaries coupled with the high degree of crystallinity. Furthermore, we believe that the residual resistance measured below Tc is at present dominated by losses occurring in the substrate and the cavities rather than by losses intrinsic to the Y-Ba-Cu oxide superconductor. [ABSTRACT FROM AUTHOR]

Superlattices of YBa2Cu3O7-x/YyPr1-yBa2Cu3O7-x(y=0.8 and 0.0) have been successfully grown in situ on MgO and LaAlO3 by using a multitarget pulsed laser deposition system. Satellite peaks have been observed in x-ray diffraction for the superlattices with modulation wavelengths from about few tens of angstroms to few hundred angstroms. The x-ray diffraction measurements also indicate that the multilayers have c axis normal to the substrates. Good crystallinity has been observed in the superlattices with He ion backscattering minimum yields of about 10%, indicating highly oriented growth. The presence of a periodic layer structure was further confirmed by the observation of composition oscillations in these structures by secondary-ion mass spectrometry. [ABSTRACT FROM AUTHOR]

For a variety of device applications, junction devices in particular, we have demonstrated a heterostructure system of Y1Ba2Cu3O7-y/Y1-xPrxBa2Cu3O7-y which maintains epitaxy over the entire Pr composition range x=0–1. We have grown both trilayer and multiperiod superlattices which show nearly single crystalline helium ion backscattering minimum yields of <6% in the topmost layer. X-ray diffraction measurements indicate c-axis orientation by a transverse scan across (005) line with a full width at half maximum of 0.6° and 0.4° on MgO and SrTiO3 substrates, respectively. Scanning Auger electron depth profiles and cross-sectional transmission electron micrographs indicate abrupt Pr/Y interfaces within one unit cell and virtually no disruption of the layered structure at the interface. These results indicate the potential for the growth of excellent heterostructures and superlattices of the high-temperature superconductors. [ABSTRACT FROM AUTHOR]

A new wet chemical etchant for high-temperature superconducting films is reported, which leaves transition temperature unaffected within experimental accuracy (1 K) and does not require reoxygenation. The solution consists of ethylenediaminetetraacetic acid (EDTA) in water, and is suitable for micropatterning using standard photolithography. We have fabricated 3–50 μm patterns on laser-deposited Y-Ba-Cu-O films. The bulk of the films etches at 0.14 μm/min in a saturated solution at room temperature. Porous surface layers are removed three times faster than the dense portions of the films. Etch rate depends linearly on the solution concentration and exponentially on the solution temperature. These rates are reduced if etching is interrupted and the samples are exposed to atmosphere. [ABSTRACT FROM AUTHOR]

We report, for the first time, growth of thin films of Y-Ba-Cu-O by pulsed laser deposition onto [001] YbFeO3 single-crystal substrates. A Tc,0 of 88 K was obtained along with a critical current greater than 105 A/cm2 at 77 K. X-ray diffraction shows epitaxial growth of the 1-2-3 phase with the c axis oriented normal to the substrate plane. Rocking curve measurements show a 0.5° full width at half maximum, indicating good alignment of the layered structure. The composition was verified by Rutherford backscattering, while channeling results reveal a 17% yield, consistent with the rocking curve measurements. Growth of thin films of 1-2-3 on a magnetic substrate may open the way for potentially new applications. [ABSTRACT FROM AUTHOR]

The microstructure of in situ epitaxially grown Y-Ba-Cu-O thin films on (001) SrTiO3 substrates was studied using cross-sectional transmission electron microscopy. The films, prepared by pulsed laser deposition at substrate holder temperature of 650 °C without post-annealing, exhibit zero resistivity above 90 K and critical currents exceeding 106 A/cm2 at 77 K. The films are of heavily faulted single crystalline structure with the c axis approximately perpendicular to the substrate (001) surface. We suggest that, due to the fast quenching and low substrate temperature, crystalline defects and chemical fluctuations are locked into a faulted structure after each laser pulse. Despite their rather imperfect microstructure, the films are free from macroscopic grain boundaries and secondary phases and possess superb superconducting properties. [ABSTRACT FROM AUTHOR]

A standard 600 °C closed-tube Zn diffusion into an unstrained InP/In0.53Ga0.47As superlattice was found to produce new superlattices containing Zn3P2 layers, and in some cases Zn3As2 layers. Crystalline properties and diffusion profiles were examined by transmission electron microscopy and secondary-ion mass spectrometry. Initial doping of Zn enhances the diffusion of In and Ga and results in a superlattice of uniform In and Ga distribution. Upon further infusion of Zn, Zn3P2 forms selectively in the phosphorus layers and propagates from the surface while maintaining an atomically abrupt Zn3P2/In1-xGaxP interface. Zn3As2 conversion is also observed to occur under sufficiently stringent conditions. Diffusion of P and As was not observed. [ABSTRACT FROM AUTHOR]

As-deposited superconducting thin films (∼0.1 μm) of YBa2Cu3O7-x have been prepared by pulsed laser deposition on (100) Si with buffer layers of BaTiO3/MgAl2O4. X-ray diffraction studies reveal that the films grow epitaxially with the c axis preferentially oriented normal to the substrate surface. This is confirmed by ion channeling measurements along the (100) (normal to the surface) and (110) directions of the Si substrate showing a minimum yield of 54% along the (100), and 78% along the (110) axes using 2.8 MeV He++. Preliminary transmission electron microscopy study also supports these results. The as-deposited films have zero resistance temperatures of 86–87 K, and critical current densities of 6×104 A/cm2 at 77 K and 1.2×105 A/cm2 at 73 K. Our results indicate that the superconducting properties of the films are limited primarily by the quality and degree of epitaxal growth of the buffer layers on the silicon substrate. [ABSTRACT FROM AUTHOR]