A multi-technique comparison of the electronic properties of pristine and nitrogen-doped polycrystalline SnO2

Nitrogen-doped semiconducting oxides. Implications on photochemical, photocatalytic and electronic properties derived from EPR spectroscopy

Engineering defects in semiconducting metal oxides is a challenge that remains at the forefront of materials chemistry research. Nitrogen has emerged as one of the most attractive elements able to tune the photochemical and photocatalytic properties of semiconducting oxides, boosting visible-light harvesting and charge separation events, key elements in promoting solar driven chemical reactions. Doping with nitrogen is also a strategy suggested to obtain p-type conduction properties in oxides showing n-type features in their pristine state and to impart collective magnetic properties to the same systems. Here, we review the evolution in the understanding of the role of nitrogen doping in modifying the photochemical and electronic properties of the most common semiconducting oxides used in mentioned applications including: TiO2, ZnO, SnO2 and zirconium titanates. With an emphasis on polycrystalline materials, we highlight the unique role of Electron Paramagnetic Resonance (EPR) spectroscopy in the direct detection of open-shell N-based defects and in the definition of their structural and electronic properties. Synthetic strategies for the insertion of nitrogen defects in the various matrices are also discussed, along with the influence of the corresponding low-lying energy states on the general electronic properties of the doped solids.

A Novel High-Pressure Tin Oxynitride Sn2 N2 O

We report the first oxynitride of tin, Sn2 N2 O (SNO), exhibiting a Rh2 S3 -type crystal structure with space group Pbcn. All Sn atoms are in six-fold coordination, in contrast to Si in silicon oxynitride (Si2 N2 O) and Ge in the isostructural germanium oxynitride (Ge2 N2 O), which appear in four-fold coordination. SNO was synthesized at 20 GPa and 1200-1500 °C in a large volume press. The recovered samples were characterized by synchrotron powder X-ray diffraction and single-crystal electron diffraction in the TEM using the automated diffraction tomography (ADT) technique. The isothermal bulk modulus was determined as Bo =193(5) GPa by using in-situ synchrotron X-ray diffraction in a diamond anvil cell. The structure model is supported by DFT calculations. The enthalpy of formation, the bulk modulus, and the band structure have been calculated.

Organometallic Precursor-Derived SnO2/Sn-Reduced Graphene Oxide Sandwiched Nanocomposite Anode with Superior Lithium Storage Capacity

Benefiting from the reversible conversion reaction upon delithiation, nanosized SnO₂, with its theoretical capacity of 1494 mA h g^-1, has gained special attention as a promising anode material. Here, we report a self-assembled SnO₂/Sn-reduced graphene oxide (rGO) sandwich nanocomposite developed by organometallic precursor coating and in situ transformation. Ultrafine SnO₂ nanoparticles with an average diameter of 5 nm are sandwiched within the rGO/carbonaceous network, which not only greatly alleviates the volume changes upon lithiation and aggregation of SnO₂ nanoparticles but also facilitates the charge transfer and reaction kinetics of SnO₂ upon lithiation/delithiation. As a result, the SnO₂/Sn-rGO nanocomposite exhibited a superior lithium storage capacity with a reversible capacity of 1307 mA h g^-1 at a current density of 80 mA g^-1 in the potential window of 0.01-2.5 V versus Li⁺/Li and showed a reversible capacity of 767 mA h g^-1 over 200 cycles at a current density of 400 mA g^-1. When cycling at a higher current density of 1600 mA g^-1, the SnO₂/Sn-rGO nanocomposite showed a highly stable capacity of 449 mA g^-1 without obvious decay after 400 cycles.