Fast and Durable Lithium Storage Enabled by Tuning Entropy in Wadsley-Roth Phase Titanium Niobium Oxides.

Wadsley-Roth phase titanium niobium oxides have received considerable interest as anodes for lithium ion batteries. However, the volume expansion and sluggish ion/electron transport kinetics retard its application in grid scale. Here, fast and durable lithium storage in entropy-stabilized Fe0.4 Ti1.6 Nb10 O28.8 (FTNO) is enabled by tuning entropy via Fe substitution. By increasing the entropy, a reduction of the calcination temperature to form a phase pure material is achieved, leading to a reduced grain size and, therefore, a shortening of Li+ pathway along the diffusion channels. Furthermore, in situ X-ray diffraction reveals that the increased entropy leads to the decreased expansion along a-axis, which stabilizes the lithium intercalation channel. Density functional theory modeling indicates the origin to be the more stable FeO bond as compared to TiO bond. As a result, the rate performance is significantly enhanced exhibiting a reversible capacity of 73.7 mAh g-1 at 50 C for FTNO as compared to 37.9 mAh g-1 for its TNO counterpart. Besides, durable cycling is achieved by FTNO, which delivers a discharge capacity of 130.0 mAh g-1 after 6000 cycles at 10 C. Finally, the potential impact for practical application of FTNO anodes has been demonstrated by successfully constructing fast charging and stable LiFePO4 ‖FTNO full cells.

Patterning titania with the conventional and modified micromolding in capillaries technique from sol-gel and dispersion solutions.

We report TiO2 patterns obtained by a soft-lithographic technique called 'micromolding in capillaries' using sol-gel and dispersion solutions. A comparison between patterning with a sol-gel and dispersion solutions has been performed. The patterns obtained from sol-gel solutions showed good adhesion to the substrate and uniform shapes, but large shrinkage, whereas those obtained from dispersion solution had high solid content, but exhibited poor adhesion and non-uniform shapes. A fabrication method of a layer-by-layer structured pattern is also demonstrated. This type of pattern may find application in sensors, waveguides and other photonics elements. The occurrence of an undesirable residue layer, which hinders the fabrication of isolated patterns, is highlighted and a method of prevention is suggested.

Growing a LaAlO3/SrTiO3 heterostructure on Ca2Nb3O10 nanosheets.

The two-dimensional electron liquid which forms between the band insulators LaAlO3 (LAO) and SrTiO3 (STO) is a promising component for oxide electronics, but the requirement of using single crystal SrTiO3 substrates for the growth limits its applications in terms of device fabrication. It is therefore important to find ways to deposit these materials on other substrates, preferably Si, or Si-based, in order to facilitate integration with existing technology. Interesting candidates are micron-sized nanosheets of Ca2Nb3O10 which can be used as seed layers for perovskite materials on any substrate. We have used low-energy electron microscopy (LEEM) with in-situ pulsed laser deposition to study the subsequent growth of STO and LAO on such flakes which were deposited on Si. We can follow the morphology and crystallinity of the layers during growth, as well as fingerprint their electronic properties with angle resolved reflected electron spectroscopy. We find that STO layers, deposited on the nanosheets, can be made crystalline and flat; that LAO can be grown in a layer-by-layer fashion; and that the full heterostructure shows the signature of the formation of a conducting interface.