3 research outputs found
Ferroelectric Mesocrystalline BaTiO<sub>3</sub>/SrTiO<sub>3</sub> Nanocomposites with Enhanced Dielectric and Piezoelectric Responses
A platelike mesocrystalline
BaTiO<sub>3</sub>/SrTiO<sub>3</sub> (BT/ST) nanocomposite is prepared
via a clever two-step solvothermal soft chemical process. First a
protonated titanate H<sub>1.07</sub>Ti<sub>1.73</sub>O<sub>4</sub>·<i>n</i>H<sub>2</sub>O (HT) crystal with a layered
structure and platelike morphology is solvothermally treated in a
BaÂ(OH)<sub>2</sub> solution to generate a homogeneous platelike BaTiO<sub>3</sub>/HT (BT/HT) nanocomposite. Second the generated BT/HT nanocomposite
is solvothermally treated in a SrÂ(OH)<sub>2</sub> solution to generate
the mesocrystalline BT/ST nanocomposite with platelike particle morphology.
The transformation reactions from the HT precursor to the mesocrystalline
BT/ST nanocomposite are topochemical conversion reactions, and the
formed BT/ST nanocomposite is constructed from well-aligned BT and
ST nanocrystals in the same crystal-axis orientation. The BT/ST nanocomposite
annealed at 900 °C shows a ferroelectric behavior and drastically
enhanced piezoelectric and dielectric responses owing to the introduction
of a lattice strain at a three-dimensional heteroepitaxial interface
between the BT and ST nanocrystals in the mesocrystal. The nanostructure
of the BT/ST mesocrystal is suitable for simultaneous application
of the strain engineering and the orientation engineering to develop
high performance piezoelectric and dielectric materials
Ferroelectric Mesocrystals of Bismuth Sodium Titanate: Formation Mechanism, Nanostructure, and Application to Piezoelectric Materials
Ferroelectric mesocrystals of Bi<sub>0.5</sub>Na<sub>0.5</sub>TiO<sub>3</sub> (BNT) with [100]-crystal-axis
orientation were successfully
prepared using a topotactic structural transformation process from
a layered titanate H<sub>1.07</sub>Ti<sub>1.73</sub>O<sub>4</sub>·<i>n</i>H<sub>2</sub>O (HTO). The formation reactions of BNT mesocrystals
in HTO–Bi<sub>2</sub>O<sub>3</sub>–Na<sub>2</sub>CO<sub>3</sub> and HTO–TiO<sub>2</sub>–Bi<sub>2</sub>O<sub>3</sub>–Na<sub>2</sub>CO<sub>3</sub> reaction systems and
their nanostructures were studied by XRD, FE-SEM, TEM, SAED, and EDS,
and the reaction mechanisms were given. The BNT mesocrystals are formed
by a topotactic structural transformation mechanism in the HTO–Bi<sub>2</sub>O<sub>3</sub>–Na<sub>2</sub>CO<sub>3</sub> reaction
system and by a combination mechanism of the topotactic structural
transformation and epitaxial crystal growth in the HTO–TiO<sub>2</sub>–Bi<sub>2</sub>O<sub>3</sub>–Na<sub>2</sub>CO<sub>3</sub> reaction system, respectively. The BNT mesocrystals prepared
by these methods are constructed from [100]-oriented BNT nanocrystals.
Furthermore, these reaction systems were successfully applied to the
fabrication of [100]-oriented BNT ferroelectric ceramic materials.
A BNT ceramic material with a high degree of orientation, high relative
density, and small grain size was achieved
Mesocrystalline Nanocomposites of TiO<sub>2</sub> Polymorphs: Topochemical Mesocrystal Conversion, Characterization, and Photocatalytic Response
Four
kinds of platelike mesocrystalline nanocomposites of TiO<sub>2</sub> polymorphs were successfully synthesized for the first time
based on a topochemical mesocrystal conversion mechanism. In this
conversion process, a [010]-oriented titanate H<sub>1.07</sub>Ti<sub>1.73</sub>â–¡<sub>0.27</sub>O<sub>4</sub> (â–¡: vacancy of Ti) single crystal
with lepidocrocite-like structure and platelike morphology was successively
transformed into [001]- and [102]-oriented TiO<sub>2</sub>(B) phases
including a {010}-faceted TiO<sub>2</sub>(B) twinning, [010]-oriented
anatase phase, and [110]-oriented rutile phase. The platelike particle
morphology is retained in the topochemical conversion process. The
platelike particles are constructed from nanocrystals which well-aligned
in the same orientation for the same phase, resulting in the formations
of HTO/TiO<sub>2</sub>(B), HTO/TiO<sub>2</sub>(B)/anatase, TiO<sub>2</sub>(B)/anatase, and anatase/rutile mesocrystalline nanocomposites.
The reaction mechanism and the crystallographic topological correspondences
between the precursor, intermediates, and the final product were given
on the basis of the nanostructural analysis results. The mesocrystalline
nanocomposite of anatase/rutile polymorphs exhibits unexpectedly high
surface photocatalytic activity, which can be explained by the superior
electron–hole separation effect and the high activity of {010}-faceted
anatase surface in the mesocrystalline nanocomposite. Such mesocrystalline
anatase/rutile nanocomposite is an ideal photocatalytic system