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Pressure-induced amorphization (PIA) in single-crystal Ta2O5 nanowires is observed at 19 GPa, and the obtained amorphous Ta2O5 nanowires show significant improvement in electrical conductivity. The phase transition process is unveiled by monitoring structural evolution with in situ synchrotron X-ray diffraction, pair distribution function, Raman spectroscopy, and transmission electron microscopy. The first principles calculations reveal the phonon modes softening during compression at particular bonds, and the analysis on the electron localization function also shows bond strength weakening at the same positions. On the basis of the experimental and theoretical results, a kinetic PIA mechanism is proposed and demonstrated systematically that amorphization is initiated by the disruption of connectivity between polyhedra (TaO6 octahedra or TaO7 bipyramids) at the particular weak-bonding positions along the a axis in the unit cell. The one-dimensional morphology is well-preserved for the pressure-induced amorphous Ta2O5, and the electrical conductivity is improved by an order of magnitude compared to traditional amorphous forms. Such pressure-induced amorphous nanomaterials with unique properties surpassing those in either crystalline or conventional amorphous phases hold great promise for numerous applications in the future.

High permittivity LaAlO3 (LAO) and LaAlOxNy (LAON) thin films have been deposited directly on a Si(100) substrate using a laser molecular-beam epitaxy technique. Metal–oxide–silicon field-effect transistors (MOSFETs) are fabricated using such LAO and LAON thin films as gate dielectrics and well-behaved transistor characteristics have been observed. High-resolution transmission electron microscopy observations indicate that LAO thin films can remain amorphous structure even after annealing at 1000°C. The small equivalent oxide thickness (EOT) of 17A is achieved for 75A LAO film with an effective dielectric constant of 17.2±1 for the whole gate stack. Furthermore, a smaller EOT, larger drive current, and lower subthreshold slope have been observed for devices with the LAON thin film. For all the devices, the gate leakage currents are at least two orders of magnitude lower than that of the same electrical thickness SiO2. Reasonable subthreshold slopes of 248 and 181mV∕dec were obtained for MOSFETs with LAO a...

High-k gate dielectric material LaAlO3 (LAO) films were deposited directly onto silicon substrates by laser molecular-beam epitaxy. The thermodynamic stability of LAO films deposited at different substrate temperatures and of LAO films postannealed at 1000 °C was studied by high-resolution transmission electron microscopy and capacitor–voltage measurements. These studies show that the interfacial reaction between the LAO film and silicon substrate is strongly correlated to the substrate temperature and ambient conditions. In oxygen containing ambient, the interfacial reaction often occurs not only during film deposition but also during the course of postannealing. LAO films annealed at 1000 °C in nitrogen ambient have better thermal stability with silicon than LAO films annealed in oxygen ambient do. Both kinds of films remain amorphous after 1000 °C annealing.

Cubic anti-perovskites with general formula Li3OX (X = Cl, Br, I) were recently reported as superionic conductors with the potential for use as solid electrolytes in all-solid-state lithium ion batteries. These electrolytes are nonflammable, low-cost, and suitable for thermoplastic processing. However, the primary obstacle of its practical implementation is the relatively low ionic conductivity at room temperature. In this work, we synthesized a composite material consisting of two anti-perovskite phases, namely, cubic Li3OBr and layered Li7O2Br3, by solid state reaction routes. The results indicate that with the phase fraction of Li7O2Br3 increasing to 44 wt. %, the ionic conductivity increased by more than one order of magnitude compared with pure phase Li3OBr. Formation energy calculations revealed the meta-stable nature of Li7O2Br3, which supports the great difficulty in producing phase-pure Li7O2Br3 at ambient pressure. Methods of obtaining phase-pure Li7O2Br3 will continue to be explored, including both high pressure and metathesis techniques.

Epitaxial layered ternary metal-nitride FeMoN2, (Fe0.33Mo0.67)MoN2, CoMoN2, and FeWN2 thin films have been grown on c-plane sapphire substrates by polymer-assisted deposition. The ABN2 layer sits on top of the oxygen sublattices of the substrate with three possible matching configurations due to the significantly reduced lattice mismatch. The doping composition and elements affect not only the out-of-plane lattice parameters but also the temperature-dependent electrical properties. These films have resistivity in the range of 0.1–1 mΩ·cm, showing tunable metallic or semiconducting behaviors by adjusting the composition. A modified parallel connection channel model has been used to analyze the grain boundary and Coulomb blockade effect on the electrical properties. The growth of the high crystallinity layered epitaxial thin films provides an avenue to study the composition-structure-property relationship in ABN2 materials through A and B-site substitution.

Antiperovskite Li3OCl superionic conductor films are prepared via pulsed laser deposition using a composite target. A significantly enhanced ionic conductivity of 2.0 × 10−4 S cm−1 at room temperature is achieved, and this value is more than two orders of magnitude higher than that of its bulk counterpart. The applicability of Li3OCl as a solid electrolyte for Li‐ion batteries is demonstrated.

The polyhedral CoS(2) with a narrow size distribution was synthesized by a facile solid-state assembly process in a sealed silica tube. The flux of potassium halide (KX; X = Cl, Br, I) plays a crucial role in the formation of polyhedrons and the size distribution. The S(2)(2-) groups in CoS(2) can be controllably withdrawn during heat treatment in air. The obtained phases and microstructures of CoS(2), Co(3)S(4), CoS, Co(9)S(8), and CoO depended on heating temperature and time. These cobalt materials, successfully used as the electrodes of lithium ion batteries, possessed good cycling stability in lithium ion batteries. The discharge capacities of 929.1 and 835.2 mAh g(-1) were obtained for CoS(2) and CoS respectively, and 76% and 71% of the capacities remained after 10 cycles. High capacities and good cycle performance make them promising candidates for lithium ion batteries. The approach combining solid-state assembly and heat treatment provides a simple and versatile way to prepare various metal chalcogeides for energy storage applications.

A one-step high-temperature hydrated-sulfate assisted solvothermal method has been developed to synthesize TiO(2)/sulfide nanocomposite spheres. Different hybrid spheres of TiO(2)/CdS, TiO(2)/Cu(2)S, TiO(2)/FeS, TiO(2)/Co(9)S(8), and TiO(2)/ZnS were readily prepared by exploiting different hydrated sulfate. The hydrated sulfate has been proved to play multifunctional roles during the synthetic process, such as spherical template, water supplier, and composition controller. Nanocrystal CdS can be reduced from CdSO(4) at a high solvothermal temperature of 350 °C, and the TiO(2)/CdS nanocomposite spheres prepared by this method exhibit superior visible-light-driven photocatalytic efficiency because of its effective heterointerface and high crystallinity.

Single-crystalline uniform Ta(2)O(5) nanowires are prepared by a novel synthetic route. The formation of the nanowires involves an oriented attachment process caused by the reduction of surface energy. The nanowires are successfully applied to photocatalytic H(2) evolution, contaminant degradation, and dye-sensitized solar cells (DSCs). The Ta(2)O(5)-based DSCs reveal a significant photovoltaic response, which has not been reported. As a photocatalyst, the Ta(2)O(5) nanowires possess high H(2) evolution efficiency under Xe lamp irradiation, nearly 27-fold higher than the commercial powders. A better performance of photocatalytic contaminant degradation is also observed. Such improvements are ascribed to better charge transport ability for the single-crystalline wire and a higher potential energy of the conduction band. This new synthetic approach using a water-soluble precursor provides a versatile way to prepare nanostructured metal oxides.

Amino acids, as a particularly important type of biomolecules, have been used as multifunctional templates to intelligently construct mesoporous TiO(2) hollow structures through a simple solvothermal reaction. The structure-directing behaviors of various amino acids were systematically investigated, and it was found that these biomolecules possess the general capability to assist mesoporous TiO(2) hollow-sphere formation. At the same time, the nanostructures of the obtained TiO(2) are highly dependent on the isoelectric points (pI) of amino acids. Their molecular-structure variations can lead to pI differences and significantly influence the final TiO(2) morphologies. Higher-pI amino acids (e.g., L-lysine and L-arginine) have better structure-directing abilities to generate nanosheet-assembled hollow spheres and yolk/shell structures. The specific morphologies and mesopore size of these novel hollow structures can also be tuned by adjusting the titanium precursor concentration. Heat treatment in air and vacuum was further conducted to transform the as-prepared structures to porous nanoparticle-assembled hollow TiO(2) and TiO(2)/carbon nanocomposites, which may be potentially applied in the fields of photocatalysts, dye-sensitized solar cells, and Li batteries. This study provides some enlightenment on the design of novel templates by taking advantage of biomolecules.

Well-crystallized MSb(2)O(6) (M = Ca, Sr and Ba) powders synthesized by solid state reactions exhibit an interesting photocatalytic activity order of BaSrCa for organic pollutant (methylene blue and phenol) degradation and hydrogen production from water under UV light irradiation. A simple model, crystal packing factor (PF), was introduced to account for the activity difference. Nine series of photocatalysts involving 26 compounds were experimentally investigated to further substantiate the model, a lower PF being correlated to a higher photocatalytic activity. This correlation between packing factor and photocatalytic activity also holds for some 40 literature examples of 83 compounds of d(0) cations and d(10) cations. This applicable criterion for ranking photocatalytic materials of similar chemistry or structure can be rationalized through the influence of structural packing on carrier lifetimes and mobilities.

Here, we propose a unique architecture based on directly growing TiO2 nanotubes on graphene sheets. This work establishes the benefits of combining nanotubular TiO2 with conductive graphene to achieve a significant enhancement in capacitive energy storage. The TiO2 nanotubes possess a porous structure and a higher surface area compared with its bulk material. The graphene sheets play an important role in the conductive substrate for charge collection. In the preparation process, amorphous TiO2 colloids coated on graphene oxide (GO) sheets serve as the seeds to realize the growth of nanotubes, and ensure the robust contact between graphene and TiO2 nanotubes to benefit charge transfer. When used as anodes for lithium ion batteries, the graphene–TiO2 nanotubes (Gr–TNTs) manifest excellent rate capability and cycling performance, indicating that the nanotubes, graphene and their synergistic effect can prompt fast charge transfer in such a composite structure.

Nonmetal-doped black titania is achieved in a core–shell structure by a two-step synthesis. The nonmetal dopants in amorphous TiO2−x shells decrease e–h recombination centers, and more than 6.6 at.% N further improves solar energy absorption from 65% up to 85%. The photocatalytic H2 generation of the N-doped black titania is 15.0 mmol h−1 g−1 under 100 mW cm−2 of full-sunlight and 200 μmol h−1 g−1 under 90 mW cm−2 of visible-light irradiation, superior to TiO2−x and reported titania photocatalysis.

Black platelike brookite with outstanding photocatalytic performance is prepared by constructing a distinct crystalline core/disordered shell structure (TiO2@TiO2−x) through aluminium reduction. Many oxygen vacancies and Ti3+ states are introduced into the distorted shell, which increase the solar energy absorption and boost the photocatalytic activity.

With the aid of the slow release of water from esterification reactions, a simple one-step solvothermal method was developed to prepare TiO2 hollow spheres with an opening hole. Organic carboxylic acids (CA) were exploited as not only the reactant to conduct esterification with ethanol, but also the coordination agent to modify titanium n-butoxide (TNB) to manipulate its hydroxylation and condensation process. The specific TiO2 morphologies prepared by this CA-assisted method significantly depend on the molecular structure and relative concentration of the carboxylic acids used. Appropriate carbon chain length of the CA molecule and the optimal molar ratio of CA/TNB are the essential factors to fabricate well-developed TiO2 hollow spheres with an opening hole. The surface hole facilitates active material transportation into the hollow interior, so this structure of TiO2 has been utilized in lithium-ion batteries and exhibits superiority in rate performance compared to closed spheres.

High-yield three dimensional (3D) graphene networks were prepared on Ni foams by ambient pressure chemical vapour deposition (APCVD). The layer number of graphene can be tuned by changing the gas flow ratio and growth time. The assembled films from the vacuum filtration of the 3D graphene possessed excellent electrical transport properties (Rs ∼ 0.45 Ω/sq, σ ∼ 600 S cm−1), superior to the reported graphene and carbon nanotube films. Highly conductive films as back electrodes of CdTe solar cells significantly improved the photovoltaic efficiency (9.1%).

Band structure design plays a vital role on the development of highly efficient and visible-light driven photocatalysts. Large band dispersions ensure a fair mobility of the photoinduced charge carriers, leading to excellent photocatalysis. As a case in point, Bi2Sn2O7 has been investigated for the first time as a robust visible-light photocatalyst. The VB and CB are both highly dispersed, and contain s orbitals (Bi 6p + Sn 5s + O 2p for CB, O 2p + Bi 6s for VB). Bi2Sn2O7 was prepared by a direct hydrothermal reaction in the absence of additives and exhibited improved performance. This study not only discloses insights into the design of new photocatalysts in term of band engineering, but also provides flexibility and selectivity for the deliberate synthesis of other functional materials.

High-quality graphene nanosheets are prepared via a rapid Wurtz-type reductive coupling (WRC) reaction without the assistance of any transition metal catalysts. This method involves a nearly stoichiometric reaction of tetrachloromethane (CCl4) and potassium (K) at 150–210 °C for as short as 10 min, which possesses great advantages compared with the solvothermal method. The layer number of the as-prepared graphene is mainly less than five. The formation mechanism of graphene is proposed, which comprises of three steps, stripping off the chlorines from CCl4 by the highly reductive K, the coupling and assembly of –CC– and the layer growth of hexagonal carbon clusters to form graphene. Many important factors determining the quality of graphene, such as the residual chlorines, the reaction temperature and the reductant, are discussed in detail. The low residual chlorine in the reaction favors the improvement of the graphene quality. Furthermore, controllable boron doping can be easily realized by adding an appropriate amount of BBr3. The developed method provides a cost-effective route to prepare high-quality pristine or doped graphene for mass production.

The simplest amino acid, glycine (C2H5NO2), was used as a multifunctional smart template to prepare mesoporous hollow TiO2 microspheres via a facile solvothermal method. In the fabrication process, glycine serves concurrently as a sacrificial template, complexing agent and water supplier. The hollow spheres were characterized as TiO2/organic hybrid structures and converted into well-defined mesoporous structures by calcination. The growth mechanism of the hollow spheres was demonstrated to include the self-conglobated smart template above the softening temperature, a consequent in situ hydrolysis on the template surface and then a sacrificial core evacuation process. From the demonstrated mechanism, the cavity volume can be easily controlled by the mass of crude glycine used. This novel method has successfully been applied in the synthesis of Eu-doped TiO2 hollow spheres. The Eu-doped sample exhibits stronger photoluminescence owing to the unique microstructures, compared to conventional hydrothermal samples.

In view of the current attentions to energy shortages and environment crises, the development of highly efficient and visible-light driven photocatalysts becomes an urgent and important issue. The past two decades have witnessed great efforts on the d10-based metal oxides due to excellent electron conduction in dispersed conduction band (CB). The photocatalytic performance will be further enhanced if the valence band (VB) can also be modified to a hybridized state to promote the hole mobility. Here for the first time, spindle-shaped BiSbO4 nanocrystals with dispersed band structures have been prepared via a one-pot hydrothermal route without the use of additives. The quasi-one-dimensional BiSbO4 nanocrystals with larger surface area were investigated as excellent visible-light photocatalysts and showed enhanced activity for the decomposition of organic pollutants than the bulk catalyst prepared by the solid-sate reaction. This study provides insights into the design of new photocatalysts in term of band engineering and soft-chemistry synthesis.

Cubic pyrochlore niobates (A2Nb2O7, Fd-3m) have been shown to exhibit excellent photocatalytic performance and solid niobic acids show great advantages over these niobate photocatalysts. But no pyrochlore niobic acid has been reported. Here we develop a new and one-pot hydrothermal route for high-yield controlled synthesis of pyrochlore H4Nb2O7 with no aid of additives. Combined with the intrinsic loosely pyrochlore structure, the “acidity-promoted effect”, and the high crystallinity, the novel H4Nb2O7 exhibits outstanding photocatalytic activity, i.e., the reaction rate constant of H4Nb2O7 is almost 3 times of that for its amorphous precursor Am–Nb2O5.nH2O, and almost 2 times that of its corresponding calcium pyroniobate. This study discloses insights for the designed strategy of efficient photocatalysts with synergistic features, and this route provides flexibility and selectivity for the deliberate synthesis of other functional materials.