195 research outputs found

    An EPR investigation of the dynamic Jahn-Teller effect in SrCl2-La/2 plus/

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    Second-order solutions of Hamiltonian functions for EPR study of Jahn-Teller effect in SrCl2-La/2 plus

    Tetragonal tungsten bronze compounds: relaxor vs mixed ferroelectric - dipole glass behavior

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    We demonstrate that recent experimental data (E. Castel et al J.Phys. Cond. Mat. {\bf 21} (2009), 452201) on tungsten bronze compound (TBC) Ba2_2Prx_xNd1−x_{1-x}FeNb4_4O15_{15} can be well explained in our model predicting a crossover from ferroelectric (x=0x=0) to orientational (dipole) glass (x=1x=1), rather then relaxor, behavior. We show, that since a "classical" perovskite relaxor like Pb(Mn1/3_{1/3} Nb2/3_{2/3})O3_3 is never a ferroelectric, the presence of ferroelectric hysteresis loops in TBC shows that this substance actually transits from ferroelectric to orientational glass phase with xx growth. To describe the above crossover theoretically, we use the simple replica-symmetric solution for disordered Ising model.Comment: 5 two-column pages, 4 figure

    Growth, Characterization, and Electrochemical Properties of Doped n-Type KTaO_3 Photoanodes

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    The effects of compositionally induced changes on the semiconducting properties, optical response, chemical stability, and overall performance of KTaO_3 photoanodes in photoelectrochemical (PEC) cells have been investigated. Single crystals of n-type Ca- and Ba-doped KTaO_3 with carrier concentrations ranging from 0.45 to 11.5×10^(19) cm^(−3) were grown and characterized as photoanodes in basic aqueous electrolyte PEC cells. The PEC properties of the crystals, including the photocurrent, photovoltage, and flatband potential in contact with 8.5 M NaOH(aq) were relatively independent of whether Ca or Ba was used to produce the semiconducting form of KTaO_3. All of the Ca- or Ba-doped KTaO_3 single-crystal photoanodes were chemically stable in the electrolyte and, based on the open-circuit potential and the band-edge positions, were capable of unassisted photochemical H_2 and O_2 evolution from H_2O. The minority-carrier diffusion lengths values were small and comparable to the depletion region width. Photoanodic currents were only observed for photoanode illumination with light above the bandgap (i.e., λ<340 nm). The maximum external quantum yield occurred at λ=255 nm (4.85 eV), and the depletion width plus the minority-carrier diffusion length ranged from 20 to 65 nm for the various KTaO_3-based photoanode materials

    X-ray photoelectron spectroscopy study of irradiation-induced amorphizaton of Gd2Ti2O7Gd2Ti2O7

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    The radiation-induced evolution of the microstructure of Gd2Ti2O7,Gd2Ti2O7, an important pyrochlore phase in radioactive waste disposal ceramics and a potential solid electrolyte and oxygen gas sensor, has been characterized using transmission electron microscopy and x-ray photoelectron spectroscopy. Following the irradiation of a Gd2Ti2O7Gd2Ti2O7 single crystal with 1.5 MeV Xe+Xe+ ions at a fluence of 1.7×1014 Xe+/cm2,1.7×1014Xe+/cm2, cross-sectional transmission electron microscopy revealed a 300-nm-thick amorphous layer at the specimen surface. X-ray photoelectron spectroscopy analysis of the Ti 2p2p and O 1s1s electron binding energy shifts of Gd2Ti2O7Gd2Ti2O7 before and after amorphization showed that the main results of ion-irradiation-induced disorder are a decrease in the coordination number of titanium and a transformation of the Gd–O bond. These features resemble those occurring in titanate glass formation, and they have implications for the chemical stability and electronic properties of pyrochlores subjected to displacive radiation damage. © 2001 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71018/2/APPLAB-79-13-1989-1.pd

    Simultaneous formation of surface ripples and metallic nanodots induced by phase decomposition and focused ion beam patterning

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    We report the simultaneous formation of self-assembled surface ripples in Cd2Nb2O7Cd2Nb2O7 pyrochlore caused by focused ion beam (FIB) patterning and uniformly distributed metallic nanodots induced by phase decomposition under ion bombardment. The characteristic wavelength of the surface ripples is controllable from the nm to the sub-μmsub-μm scale. High-density Cd metallic nanoparticles, ∼ 5 nm∼5nm, formed and the distribution of nanoparticles is consistent with the morphological characteristics of the ripple pattern. This approach provides a means of fabricating surface nanostructure with various patterns and a controllable particle size and distribution by combining ion beam-induced phase decomposition with high-precision FIB patterning.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87787/2/093112_1.pd
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