59 research outputs found
Structural evolution of epitaxial SrCoOx films near topotactic phase transition
Control of oxygen stoichiometry in complex oxides via topotactic phase
transition is an interesting avenue to not only modifying the physical
properties, but utilizing in many energy technologies, such as energy storage
and catalysts. However, detailed structural evolution in the close proximity of
the topotactic phase transition in multivalent oxides has not been much
studied. In this work, we used strontium cobaltites (SrCoOx) epitaxially grown
by pulsed laser epitaxy (PLE) as a model system to study the oxidation-driven
evolution of the structure, electronic, and magnetic properties. We grew
coherently strained SrCoO2.5 thin films and performed post-annealing at various
temperatures for topotactic conversion into the perovskite phase
(SrCoO3-{\delta}). We clearly observed significant changes in electronic
transport, magnetism, and microstructure near the critical temperature for the
topotactic transformation from the brownmillerite to the perovskite phase.
Nevertheless, the overall crystallinity was well maintained without much
structural degradation, indicating that topotactic phase control can be a
useful tool to control the physical properties repeatedly via redox reactions.Comment: 16 pages, 4 figure
Macroscopic visualization of fast electrochemical reaction of SrCoOx oxygen sponge
Strontium cobaltite (SrCoOx) is known as a material showing fast topotactic
electrochemical Redox reaction so-called oxygen sponge. Although atomic scale
phenomenon of the oxidation of SrCoO2.5 into SrCoO3 is known, the macroscopic
phenomenon has not been clarified yet thus far. Here, we visualize the
electrochemical oxidation of SrCoOx macroscopically. SrCoOx epitaxial films
with various oxidation states were prepared by the electrochemical oxidation of
SrCoO2.5 film into SrCoO3-d film. Steep decrease of both resistivity and the
absolute value of thermopower of electrochemically oxidized SrCoOx epitaxial
films indicated the columnar oxidation firstly occurred along with the surface
normal and then spread in the perpendicular to the normal. Further, we directly
visualized the phenomena using the conductive AFM. This macroscopic image of
the electrochemical oxidation would be useful to develop a functional device
utilizing the electrochemical redox reaction of SrCoOx.Comment: 24 pages, 5 figures, 5 supplementary figure
Strongly coupled phase transition in ferroelectric/correlated electron oxide heterostructures
We fabricated ultrathin ferroelectric/correlated electron oxide
heterostructures composed of the ferroelectric Pb(Zr0.2Ti0.8)O3 and the
correlated electron oxide (CEO) La0.8Sr0.2MnO3 on SrTiO3 substrates by pulsed
laser epitaxy. The hole accumulation in the ultrathin CEO layer was
substantially modified by heterostructuring with the ferroelectric layer,
resulting in an insulator-metal transition. In particular, our thickness
dependent study showed that drastic changes in transport and magnetic
properties were strongly coupled to the modulation of charge carriers by
ferroelectric field effect, which was confined to the vicinity of the
interface. Thus, our results provide crucial evidence that strong ferroelectric
field effect control can be achieved in ultrathin (10 nm) heterostructures,
yielding at least a 100,000-fold change in resistivity
Growth and characterization of multiferroic BiMnO thin films
We have grown epitaxial thin films of multiferroic BiMnO using pulsed
laser deposition. The films were grown on SrTiO (001) substrates by
ablating a Bi-rich target. Using x-ray diffraction we confirmed that the films
were epitaxial and the stoichiometry of the films was confirmed using Auger
electron spectroscopy. The films have a ferromagnetic Curie temperature ()
of 855 K and a saturation magnetization of 1 /Mn. The electric
polarization as a function of electric field () was measured using an
interdigital capacitance geometry. The plot shows a clear hysteresis that
confirms the multiferroic nature of the thin films.Comment: 4 pages, 4 figures, submitted to J. Appl. Phy
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