NiO is a p-type wide bandgap semiconductor of use in various electronic devices ranging from solar cells to transparent transistors. This work reports the controlling of conductivity and increase of work functions by Li doping.

We have directly measured the band gap renormalization associated with the Moss-Burstein shift in the perovskite transparent conducting oxide (TCO), La-doped BaSnO 3 , using hard x-ray photoelectron spectroscopy. We determine that the band gap renormalization is almost entirely associated with the evolution of the conduction band. Our experimental results are supported by hybrid density functional theory supercell calculations. We determine that unlike conventional TCOs where interactions with the dopant orbitals are important, the band gap renormalization in La-BaSnO 3 is driven purely by electrostatic interactions.

Tensile strain along the cR-axis in epitaxial VO2 films raises the temperature of the metal insulator transition and is expected to stabilize the intermediate monoclinic M2 phase. We employ surfacesensitive x-ray spectroscopy to distinguish from the TiO2 substrate and identify the phases of VO2 as a function of temperature in epitaxial VO2/TiO2 thin films with well defined biaxial strain. Although qualitatively similar to our Landau-Ginzburg theory predicted phase diagrams, the stabilization of the M2 phase in epitaxial films results from nearly an order of magnitude more strain than expected. Our results reveal that the elongation of the cR axis is insufficient for describing the transition pathway of VO2 epitaxial films and that a strain induced increase of electron correlation effects must be considered.

For layered oxide cathodes, impedance growth and capacity fade related to reactions at the cathode-electrolyte interface (CEI) are particularly prevalent at high voltage and high temperatures. At a minimum, the CEI layer consists of Li2CO3, LiF, reduced (relative to the bulk) metal-ion species, and salt decomposition species but conflicting reports exist regarding their progression during (dis)charging. Utilizing transport measurements in combination with x-ray and nuclear magnetic resonance spectroscopy techniques, we study the evolution of these CEI species as a function of electrochemical and thermal stress for LiNi0.8Co0.15Al0.05O2 (NCA) particle electrodes using a LiPF6 ethylene carbonate: dimethyl carbonate (1:1 volume ratio) electrolyte. Although initial surface metal reduction does correlate with surface Li2CO3 and LiF, these species are found to decompose upon charging and are absent above 4.25 V. While there is trace LiPF6 breakdown at room temperature above 4.25 V, thermal aggravation is found to strongly promote salt breakdown and contributes to surface degradation even at lower voltages (4.1 V). An interesting finding of our work was the partial reformation of LiF upon discharge which warrants further consideration for understanding CEI stability during cycling.