5 research outputs found
Nanoscale Lamellar Monoclinic Li<sub>2</sub>MnO<sub>3</sub> Phase with Stacking Disordering in Lithium-Rich and Oxygen-Deficient Li<sub>1.07</sub>Mn<sub>1.93</sub>O<sub>4āĪ“</sub> Cathode Materials
The powdered crystalline samples
of nominal composition Li<sub>1.07</sub>Mn<sub>1.93</sub>O<sub>4āĪ“</sub> have been investigated by transmission electron microscopy (TEM)
combined with X-ray powder diffraction (XRD) at room temperature.
As suggested by the TEM observation, the dominant phase of the particles
is a cubic spinel Li<sub>1+Ī±</sub>Mn<sub>2āĪ±</sub>O<sub>4āĪ“</sub> with space group <i>Fd</i>3Ģ
<i>m</i>. A monoclinic Li<sub>2</sub>MnO<sub>3</sub> phase with <i>C</i>2/<i>m</i> space group was
also identified. Furthermore, the occurrence of nanoscale rotational
twinning domains in Li<sub>2</sub>MnO<sub>3</sub> with 120Ā° rotation
angles, stacked along the [103]<sub>m</sub>/[111]<sub>c</sub> (āmā
and ācā represent the monoclinic and cubic descriptions,
respectively) axis was also observed. These nanoscale rotational twining
domains are responsible for the pseudo-3-fold axis and their formation
is supported by the superstructure reflections in selected-area electron-diffraction
(SAED) patterns. Similar patterns were reported in the literature
but may have been misinterpreted without the consideration of such
domains. Consistent with the TEM observation, the XRD results reveal
the increasing percentage of monoclinic Li<sub>2</sub>MnO<sub>3</sub> with increasing annealing time, associated with more oxygen vacancies.
In addition, the electron beam irradiation during TEM studies may
cause the nucleation of nanoscale cubic spinel LiāMnāO
crystallites on the monoclinic Li<sub>2</sub>MnO<sub>3</sub> grains.
These results provide the detailed structural information about the
Li<sub>1.07</sub>Mn<sub>1.93</sub>O<sub>4āĪ“</sub> samples
and advance the understanding of corresponding electrochemical properties
of this material as well as other layer structured cathode materials
for lithium-ion batteries
Single Sublattice Endotaxial Phase Separation Driven by Charge Frustration in a Complex Oxide
Complex
transition-metal oxides are important functional materials
in areas such as energy and information storage. The cubic ABO<sub>3</sub> perovskite is an archetypal example of this class, formed
by the occupation of small octahedral B-sites within an AO<sub>3</sub> network defined by larger A cations. We show that introduction of
chemically mismatched octahedral cations into a cubic perovskite oxide
parent phase modifies structure and composition beyond the unit cell
length scale on the B sublattice alone. This affords an endotaxial
nanocomposite of two cubic perovskite phases with distinct properties.
These locally B-site cation-ordered and -disordered phases share a
single AO<sub>3</sub> network and have enhanced stability against
the formation of a competing hexagonal structure over the single-phase
parent. Synergic integration of the distinct properties of these phases
by the coherent interfaces of the composite produces solid oxide fuel
cell cathode performance superior to that expected from the component
phases in isolation
A Polar Corundum Oxide Displaying Weak Ferromagnetism at Room Temperature
Combining long-range magnetic order with polarity in
the same structure
is a prerequisite for the design of (magnetoelectric) multiferroic
materials. There are now several demonstrated strategies to achieve
this goal, but retaining magnetic order above room temperature remains
a difficult target. Iron oxides in the +3 oxidation state have high
magnetic ordering temperatures due to the size of the coupled moments.
Here we prepare and characterize ScFeO<sub>3</sub> (SFO), which under
pressure and in strain-stabilized thin films adopts a polar variant
of the corundum structure, one of the archetypal binary oxide structures.
Polar corundum ScFeO<sub>3</sub> has a weak ferromagnetic ground state
below 356 Kīøthis is in contrast to the purely antiferromagnetic
ground state adopted by the well-studied ferroelectric BiFeO<sub>3</sub>
A Polar Corundum Oxide Displaying Weak Ferromagnetism at Room Temperature
Combining long-range magnetic order with polarity in
the same structure
is a prerequisite for the design of (magnetoelectric) multiferroic
materials. There are now several demonstrated strategies to achieve
this goal, but retaining magnetic order above room temperature remains
a difficult target. Iron oxides in the +3 oxidation state have high
magnetic ordering temperatures due to the size of the coupled moments.
Here we prepare and characterize ScFeO<sub>3</sub> (SFO), which under
pressure and in strain-stabilized thin films adopts a polar variant
of the corundum structure, one of the archetypal binary oxide structures.
Polar corundum ScFeO<sub>3</sub> has a weak ferromagnetic ground state
below 356 Kīøthis is in contrast to the purely antiferromagnetic
ground state adopted by the well-studied ferroelectric BiFeO<sub>3</sub>
A Polar Corundum Oxide Displaying Weak Ferromagnetism at Room Temperature
Combining long-range magnetic order with polarity in
the same structure
is a prerequisite for the design of (magnetoelectric) multiferroic
materials. There are now several demonstrated strategies to achieve
this goal, but retaining magnetic order above room temperature remains
a difficult target. Iron oxides in the +3 oxidation state have high
magnetic ordering temperatures due to the size of the coupled moments.
Here we prepare and characterize ScFeO<sub>3</sub> (SFO), which under
pressure and in strain-stabilized thin films adopts a polar variant
of the corundum structure, one of the archetypal binary oxide structures.
Polar corundum ScFeO<sub>3</sub> has a weak ferromagnetic ground state
below 356 Kīøthis is in contrast to the purely antiferromagnetic
ground state adopted by the well-studied ferroelectric BiFeO<sub>3</sub>