A new form of TiO2 microspheres comprised of anatase/TiO2‐B ultrathin composite nanosheets has been synthesized successfully and used as Li‐ion storage electrode material. By comparison between samples obtained with different annealing temperatures, it is demonstrated that the anatase/TiO2‐B coherent interfaces may contribute additional lithium storage venues due to a favorable charge separation at the boundary between the two phases. The as‐prepared hierarchical nanostructures show capacities of 180 and 110 mAh g−1 after 1000 cycles at current densities of 3400 and 8500 mA g−1. The ultrathin nanosheet structure which provides short lithium diffusion length and high electrode/electrolyte contact area also accounts for the high capacity and long‐cycle stability.
Oil-dispersible α-NaYF4 spherical nanoparticles and β-NaYF4 hexagonal-shaped nanoplates were
synthesized by the liquid−solid two-phase approach at different reaction temperatures. The TEM and
FE-SEM images reveal that the nanoplates have a relatively narrow size distribution. In comparison with
other methods, pure β-NaYF4 hexagonal-shaped nanoplates were prepared under a relatively mild condition.
The nanoplates grew at the liquid−solid interface with slow crystallization rate, which may be preferable
for achieving β-NaYF4.
It is of great difficulty to obtain deep-UV transparent materials with enhanced second harmonic generation (SHG), mainly limited by the theoretically poor transparency of these materials in the deep-UV spectral region. Here we report a new noncentrosymmetric, deep-UV transparent phosphate RbNaMgPO, which undergoes a thermo-induced reversible phase transition (at a high temperature of 723 K) and correspondingly an evident SHG enhancement up to ∼1.5 times. The phase transition is aroused by the twist of [PO] dimers with deviation from the P-O-P equilibrium positions. Theoretical analyses reveal that the enhanced SHG can be ascribed to the thermo-induced collective alignment of SHG-active [PO] dimers along the polar axis of high-temperature phase. This work provides an unprecedented physical routine (to SHG-enhanced materials) that is distinguished from the traditional one by chemical design and synthesis.
The Ca2+ and Ba2+ solubility on Nd3+ sites in new layered perovskite NdBaInO4 mixed oxide
ionic and hole conductor and their effect on the oxide ion conductivity
of NdBaInO4 were investigated. Among the alkaline earth
metal cations Ca2+, Sr2+, and Ba2+, Ca2+ was shown to be the optimum acceptor–dopant
for Nd3+ in NdBaInO4 showing the largest substitution
for Nd3+ up to 20% and leading to oxide ion conductivities
∼3 × 10–4–1.3 × 10–3 s/cm within 600–800 °C on Nd0.8Ca0.2BaInO3.9 composition, exceeding the most-conducting Nd0.9Sr0.1BaInO3.95 in the Sr-doped NdBaInO4. Energetics of defect formation and oxygen vacancy migration
in NdBaInO4 were computed through the atomistic static-lattice
simulation. The solution energies of Ca2+/Sr2+/Ba2+ on the Nd3+ site in NdBaInO4 for creating the oxygen vacancies confirm the predominance of Ca2+ on the substitution for Nd3+ and enhancement
of the oxygen vacancy conductivity over the larger Sr2+ and Ba2+. The electronic defect formation energies indicate
that the p-type conduction in a high partial oxygen pressure range
of the NdBaInO4-based materials is from the oxidation reaction
forming the holes centered on O atoms. Both the static lattice and
molecular dynamic simulations indicate two-dimensional oxygen vacancy
migration within the perovskite slab boundaries for the acceptor-doped
NdBaInO4. Molecular dynamic simulations on the Ca-doped
NdBaInO4 specify two major vacancy migration events, respectively,
via one intraslab path along the b axis and one interslab
path along the c axis. These paths are composed by
two terminal oxygen sites within the perovskite slab boundaries.
Mo-doped SnS2 nanosheets supported on carbon cloth are synthesized. The nanosheets, as additive-free integrated electrodes for LIBs, exhibit a high initial discharge capacity, superior cycling performance and rate capability.
The 8-layered shifted hexagonal perovskite compound Ba8ZnNb6O24 was isolated via controlling the ZnO volatilization, which features long-range B-cation ordering with nanometer-scale separation by ∼1.9 nm of octahedral d(10) cationic (Zn(2+)) layers within the purely corner-sharing octahedral d(0) cationic (Nb(5+)) host. The long-range ordering of the B-site vacancy and out-of-center distortion of the highly-charged d(0) Nb(5+) that is assisted by the second-order Jahn-Teller effect contribute to this unusual B-cation ordering in Ba8ZnNb6O24. A small amount (∼15%) of d(10) Sb(5+) substitution for Nb(5+) in Ba8ZnNb6-xSbxO24 dramatically transformed the shifted structure to a twinned structure, in contrast with the Ba8ZnNb6-xTaxO24 case requiring 50% d(0) Ta(5+) substitution for Nb(5+) for such a shift-to-twin transformation. Multiple factors including B-cationic sizes, electrostatic repulsion forces, long-range ordering of B-site vacancies, and bonding preferences arising from a covalent contribution to the B-O bonding that includes out-of-center octahedral distortion and the B-O-B bonding angle could subtly contribute to the twin-shift phase competition of B-site deficient 8-layered hexagonal perovskites Ba8B7O24. The ceramics of new shifted Ba8ZnNb6O24 and twinned Ba8ZnNb5.1Sb0.9O24 compounds exhibited good microwave dielectric properties (εr ∼ 35, Qf ∼ 36 200-43 400 GHz and τf ∼ 38-44 ppm/°C).
Here, we demonstrate an effective
strategy to constitutionally
increase the conductivity and electrocatalytic property of NiFe
2
O
4
by phosphate ion functionalization. The phosphate-ion-modified
NiFe
2
O
4
(P-NiFe
2
O
4
) nanosheets
are readily grown on a carbon cloth by a simple hydrothermal method
and followed by a phosphating process. The introduction of phosphate
ions on the NiFe
2
O
4
surface is highly beneficial
for increasing the charge transport rate and electrocatalytic active
sites. As a result, the as-prepared P-NiFe
2
O
4
nanosheets show outstanding electrocatalytic activity toward oxygen
evolution reaction (OER), with a low overpotential (231 mV at 10 mA/cm
2
) and Tafel slope (49 mV/dec). Furthermore, the P-NiFe
2
O
4
electrode has a remarkable stability with no
activity fading after 50 h. In addition, the as-fabricated water electrocatalysts
exhibit excellent flexibility at the foldable state. These features
make the phosphate-ion-functionalized NiFe
2
O
4
electrodes open a new way to develop OER electrocatalysts with high
electrochemical property.
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