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In this paper, we present a unique resistive switching (RS) mechanism study of Pt/TiO2/Pt cell, one of the most widely studied RS system, by focusing on the role of interfacial bonding at the active TiO2-Pt interface, as opposed to a physico-chemical change within the RS film. This study was enabled by the use of a non-conventional scanning probe-based setup. The nanoscale cell is formed by bringing a Pt/TiO2-coated atomic force microscope tip into contact with a flat substrate coated with Pt. The study reveals that electrical resistance and interfacial bonding status are highly coupled together. An oxygen-mediated chemical bonding at the active interface between TiO2 and Pt is a necessary condition for a non-polar low-resistance state, and a reset switching process disconnects the chemical bonding. Bipolar switching mode did not involve the chemical bonding. The nature of chemical bonding at the TiO2-metal interface is further studied by density functional theory calculations.

Li2MnO3 is a critical component in the family of "Li-excess" materials, which are attracting attention as advanced cathode materials for Li-ion batteries. Here, first-principle calculations are presented to investigate the electrochemical activity and structural stability of stoichiometric LixMnO3 (0 ≤ x ≤ 2) as a function of Li content. The Li2MnO3 structure is electrochemically activated above 4.5 V on delithiation and charge neutrality in the bulk of the material is mainly maintained by the oxidization of a portion of the oxygen ions from O2- to O1-. While oxygen vacancy formation is found to be thermodynamically favorable for x < 1, the activation barriers for O2- and O1- migration remain high throughout the Li composition range, impeding oxygen release from the bulk of the compound. Defect layered structures become thermodynamically favorable at lower Li content (x < 1), indicating a tendency towards the spinel-like structure transformation. A critical phase transformation path for forming nuclei of spinel-like domains within the matrix of the original layered structure is proposed. Formation of defect layered structures during the first charge is shown to manifest in a depression of the voltage profile on the first discharge, providing one possible explanation for the observed voltage fade of the Li-excess materials.

Recent calculations and experimental data suggest that understanding the local ordering behavior of Ni/Mn will be critical to optimize the electrochemical properties of LiNi0.5Mn1.5O4 (LNMO) high voltage spinel. In this study, we systematically controlled the evolution of Ni and Mn ordering in LNMO samples by annealing them at 700 °C in air for different dwelling times, followed by quenching to room temperature. The long- and short-range ordering behavior of Ni and Mn were analyzed by combining neutron powder diffraction, X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FT-IR) data. The results show that the fraction of ordered phase increases rapidly during initial annealing at 700 °C for 6 h, and accompanied by decreasing amounts of secondary phases. Annealing longer than 6 h led to the growth in size of ordered domains (i.e., increased segregation of ordered and disordered domains) along with a slow increase in the fraction of ordered phase. The dependence of open circuit voltages (OCVs) of the LNMO on the degree of ordering agrees well with recent calculations using the density functional theory. The increase in the degree of ordering increases the open circuit voltage (OCV) and the initial capacity but reduces cycle life and rate capability. The LNMO delivered optimal battery performances (capacity, cycle life, and rate capability) after annealing at 700 °C for 2 h. This partially ordered sample showed the respective advantages from both disordered and ordered spinels: better spinel-phase purity (thus, higher initial capacity) from the ordered LNMO and better cycle life and rate capability from the disordered LNMO. © 2014 American Chemical Society.

Nano-scaling of electrode materials is often used in battery applications to enhance performance, particularly relating to rate capability. However, for the high-voltage spinel LiNi0.5Mn1.5O4 conflicting results have been reported on the benefits of nano-scaling. In this study, we present first-principles calculations to investigate the effect of nano-scaling on LiNi0.5Mn1.5O4, specifically focusing on the roles and coupling between surface stability, cation ordering and phase behavior. We calculate and compare the surface energy for the low index facets (100), (110), and (111), and find that the most stable facet is dependent on the cation ordering at the surface layer. In this context, we predict a spontaneous surface reconstruction in the cation-ordered structure which leads to a deviation from the perfect surface cation ordering and results in an enhanced accessibility to solid solution behavior as a function of Li content. Our results imply that nano-scaling will be more beneficial for the cation-ordered structure, as compared to the disordered structure where the solid solution region is already intrinsically accessible for a broad range of Li concentrations.

With the recent increase in food demand, urban agriculture has gained attention as a way of increasing food self-sufficiency and providing recreational spaces in cities. In this study, the suitability of rooftop greenhouses (RGs), a type of urban agriculture, was analyzed by combining the analytical hierarchy process (AHP) and geographic information systems (GIS) in Seoul, the capital city of Korea. To achieve this, we derived location suitability factors through expert consultations and calculated the weights of each factor through AHP. After building the spatial data according to these factors, they were weighted and summed then scaled to a score of 0–100. The highest weight of the RG location factors was for benefit (0.1782), followed by officially assessed land prices (0.0913) and supermarket density (0.0802). The weights of supermarket density and accessibility were high because they are considered the main distribution channels. When analyzing the location of RGs by linking these results with the spatial data according to factor, we revealed that Gangseo-gu (a district of Seoul) had relatively high location suitability scores. This trend was determined to be caused by the rather low officially assessed land price, high supermarket density, and productive population. This result could prove useful when selecting the approximate locations of RGs in Seoul and for promoting food self-sufficiency in cities. [ABSTRACT FROM AUTHOR]

Quantum chemistry simulations of some industrially relevant molecules are reported, employing variational quantum algorithms for near-term quantum devices. The energies and dipole moments are calculated along the dissociation curves for lithium hydride (LiH), hydrogen sulfide, lithium hydrogen sulfide, and lithium sulfide. In all cases, we focus on the breaking of a single bond to obtain information about the stability of the molecular species being investigated. We calculate energies and a variety of electrostatic properties of these molecules using classical simulators of quantum devices, with up to 21 qubits for lithium sulfide. Moreover, we calculate the ground-state energy and dipole moment along the dissociation pathway of LiH using IBM quantum devices. This is the first example, to the best of our knowledge, of dipole moment calculations being performed on quantum hardware. [ABSTRACT FROM AUTHOR]