3 research outputs found
Crystal Shape Tailoring in Perovskite Structure Rare-Earth Ferrites REFeO<sub>3</sub> (RE = La, Pr, Sm, Dy, Er, and Y) and Shape-Dependent Magnetic Properties of YFeO<sub>3</sub>
Controllable growth of perovskite
oxide with tailored shapes is
challenging but promising for shape-dependent physical and chemical
property studies and probable applications. In this article, we report
a general method for tailoring the crystal shape of perovskite structure
rare-earth ferrite (REFeO<sub>3</sub>) crystals in hydrothermal conditions.
By adjusting the ratio of KOH to urea, various shapes of REFeO<sub>3</sub> crystals can be prepared, such as LaFeO<sub>3</sub> truncated
cubes, PrFeO<sub>3</sub> perpendicular cross prisms, SmFeO<sub>3</sub> crossed bars with trustum, DyFeO<sub>3</sub> double pyramids on
cubes, ErFeO<sub>3</sub> distorted octahedrons, and YFeO<sub>3</sub> long bars and thick hexagonal elongated plates. Detailed shape tailoring
conditions for each phase of the crystals have been discussed clearly.
The structure-dependent shape growing mechanism for each REFeO<sub>3</sub> is generally discussed by consideration of the variance of
reduced unit cell parameters in reference to the ideal cubic ABO<sub>3</sub> perovskite structure. DyFeO<sub>3</sub> was taken as an example
to elucidate the crystal shape formation mechanism based on the Bravais–Friedel–Donnay–Harker
theory. The magnetic property of the YFeO<sub>3</sub> crystal shows
shape dependence: elongated bars have the highest saturated magnetization,
while the lowest coercive field, while the tailored polyhedrons are
vice versa. This paper not only builds a general technique for tailoring
the crystal shape to various shapes of REFeO<sub>3</sub> crystals
but also provides many crystals for further study and application
of anisotropy either in physical or in chemical properties
Programmable Structure Control in Cigarlike TiO<sub>2</sub> Nanofibers and UV-Light Photocatalysis Performance of Resultant Fabrics
Novel
cigarlike nanofibers with an outer-shell and inner-continuous-pore
structure and resultant fabrics have been fabricated by coupling the
self-assembly of polystyrene-<i>block</i>-polyÂ(ethylene
oxide) (PS-<i>b</i>-PEO) containing titanium precursors
with the electrospinning technique in our previous work [You et al. ACS Appl. Mater. Interfaces 2013, 5, 2278]. In the current work, the structure control in these nanofibers
has been investigated in detail using scanning electron microscopy,
focused ion beam, and small angle X-ray scattering. Our results indicate
that electrospinning conditions, the adopted solvent, the volume fraction
of PS-<i>b</i>-PEO block copolymer, and the amount of titanium
tetraisopropoxide in the mixture produce significant effects on both
outer-shell and inner-continuous structures in the nanofibers. The
parameters discussed above make it possible to achieve programmable
structure control in the aspect of the diameter, thickness of the
outer shell, and inner continuous pore. As a result, both micropores
among fibers and nanopores in certain fibers are under their control.
Furthermore, the photocatalytic activity of resultant TiO<sub>2</sub> fabrics was investigated by taking the photodegradation of Rhodamine
B as an example. The results suggest that the degradation efficiency
and rate constant exhibit sensitivity on the structure of nanofibers
Novel Cigarlike TiO<sub>2</sub> Nanofibers: Fabrication, Improved Mechanical, and Electrochemical Performances
By
coupling the self-assembly of polystyrene-block-polyÂ(ethylene oxide)
(PS-b-PEO) containing titanium precursors with the electrospinning
technique, novel cigarlike nanofibers with an outer-shell and inner-continuous-pore
structure and resultant fabrics were fabricated. Different from typical
porous metal oxides, the prepared high-surface-area nonwoven fabrics
show excellent mechanical properties. Not only are these fabrics self-supporting
over a large area, but they can also be cut using scissors, which
is important for large-scale applications. Furthermore, as electrode
materials in Li-ion batteries, these fabrics exhibit much higher charge/discharge
capacity and cycle stability compared with the commercially available
nanosized TiO<sub>2</sub> (P25). The improved mechanical and electrochemical
performances are attributed to the presence of an outer-shell, inner-bicontinuous
structures (including continuous TiO<sub>2</sub> frame and continuous
nanopores) and hierarchical pores from the cigarlike nanofibers