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Proton conducting oxide ceramics have shown potential for use in fuel cell technologies. Understanding the energy pathways for proton conduction could help us design more efficient fuel cell materials. This paper describes how octahedral tilting affects the relative energies of proton binding sites, transition states, and conduction pathways in cubic and pseudo-cubic perovskites. First, the structure for cubic and pseudo-cubic forms of BaTiO3, BaZrO3, CaTiO3, and CaZrO3, is found. Even when cubic symmetry is enforced, CaTiO3, and CaZrO3 exhibit octahedral tilting distortions characteristic of orthorhombic phases while BaTiO3 and BaZrO3 remain undistorted. Octahedral tilting gives rise to proton binding sites facilitating inter- and intra-octahedral proton transfer while the proton binding sites of undistorted perovskites facilitate only intra-octahedral proton transfer. The nudged elastic band method is used to find minimum energy paths between the proton binding sites. As distortions increase, inter-octahedral proton transfer barriers decrease while intra-octahedral proton transfer barriers increase. Concurrently, rotational barriers from oxygens facilitating inter-octahedral proton transfer increase while rotational barriers from oxygens facilitating intra-octahedral proton transfer decrease. Intra-octahedral transfer is the rate-limiting step to the lowest energy extended proton conduction pathway in all the perovskites considered. [ABSTRACT FROM AUTHOR]

A real-space pseudopotential density functional theory along with van der Waals density functional was employed to calculate the intermolecular interaction of the benzene-water complex. The results for the intermolecular potential energy surface showed a stable configuration with the water molecule standing above or below the benzene with one or both of the H atoms pointing towards the benzene plane.

High-throughput first-principles calculations are performed on ABO3 perovskites for new thermal barrier coating (TBC) materials. We present systematic investigations comprised of multiple selection criteria to achieve the prediction of target materials. A database including mechanical/thermal properties of 190 perovskites is initially established. Six perovskites are proposed as novel TBC materials with predicted thermal conductivities under 1.25 W/(m·K) and good damage tolerance. The observed anisotropy of thermal conductivity provides possibilities for the performance controlling via the growth orientation design. The adopted strategy and established database are expected to inspire the design of ABO3-based TBC materials and future structural material investigations. An investigation strategy for ceramics based on high-throughput calculations is constructed. Six perovskite oxides are predicted as new thermal barrier coating materials based on the established property database of perovskites. [ABSTRACT FROM AUTHOR]

The slow kinetics of the oxygen evolution (OER) and oxygen reduction (ORR) reactions hamper the development of renewable energy storage and conversion technologies. Transition-metal oxides (TMOs) are cost-effective replacements to conventional noble metal catalysts for driving these electrochemical systems. Strain is known to greatly affect the electronic structure of TMO surfaces, leading to significant changes in their electrocatalytic activities. In this study, we explore the influence of strain on the OER and ORR mechanisms on the LaNiO3(001) surface using density functional theory (DFT). Through a comparison of the overpotential and the largest change in Gibbs free energy (ΔG) in the reaction pathway, we determined that the OER activity on the LaNiO3 surface is directly related to the desorption of –H from the surface, which can be tuned as a function of strain. Moreover, tensile strain shuts off the reaction pathway to forming the –O2H intermediate state, due to the dissociation of –O2H into –O2 and –H. This is largely a consequence of the strong binding of H to the surface O, leading to a significant increase in the largest ΔG for the ORR on the tensile-strained surfaces by promoting an alternative reaction pathway. Overall, our results show that tensile strain on LaNiO3(001) leads to a decrease in both OER and ORR activities. Interestingly, in both cases, we find that the reaction is driven by the interactions with surface O ions, thus calling for a reinterpretation of the role that Ni eg orbital polarization plays in defining the OER and ORR catalytic activity on the TMO surfaces. Here, it is an indirect measure of changes in Ni–O hybridization, which controls the binding of –H species to the surface. As such, these results highlight the importance of surface O ions; particularly as it relates to defining molecule–surface interactions that ultimately tune and enhance the electrocatalytic efficiency of perovskite materials through the modulation of strains. [ABSTRACT FROM AUTHOR]

Defects formed during chemical vapor deposition (CVD) of two-dimensional (2D) transition metal dichalcogenides (TMDs) currently limit their quality and optoelectronic properties. Effective synthesis and processing strategies to suppress defects and enhance the quality of 2D TMDs are urgently needed to enable next generation optoelectronic devices. In this work, isoelectronic doping is presented as a new strategy to form stable alloys and suppress defects and enhance photoluminescence (PL) in CVD-grown TMD monolayers. The isoelectronic substitution of W atoms for Mo atoms in CVD-grown monolayers of Mo1- x W x Se2 (0 < x < 0.18) is shown to effectively suppress Se vacancy concentration by 50% compared to those found in pristine MoSe2 monolayers, resulting in a decrease in defect-mediated nonradiative recombination, ≈10 times more intense PL, and an increase in the carrier lifetime by a factor of 3. Theoretical predictions reveal that isoelectronic W alloying to form Mo1- x W x Se2 monolayers raises the energy of deep level defects in MoSe2 to enable faster quenching, which is confirmed by low temperature (4-125 K) PL from defect-related localized states. Isoelectronic substitution therefore appears to be a promising synthetic method to control the heterogeneity of 2D TMDs to realize the scalable production of high performance optoelectronic and electronic devices. [ABSTRACT FROM AUTHOR]

Atomically disordered oxides have attracted significant attention in recent years due to the possibility of enhanced ionic conductivity. However, the correlation between atomic disorder, corresponding electronic structure, and the resulting oxygen diffusivity is not well understood. The disordered variants of the ordered pyrochlore structure in gadolinium titanate (Gd2Ti2O7) are seen as a particularly interesting prospect due to intrinsic presence of a vacant oxygen site in the unit atomic structure, which could provide a channel for fast oxygen conduction. In the present work, we provide insights into the subangstrom scale on the disordering-induced variations in the local atomic environment and its effect on the electronic structure in high-energy ion irradiation-induced disordered nanochannels, which can be utilized as pathways for fast oxygen ion transport. With the help of an atomic plane-by-plane-resolved analyses, the work shows how the presence of various types of TiOx polyhedral that exist in the amorphous and disordered crystalline phase modify the electronic structures relative to the ordered pyrochlore phase in Gd2Ti2O7. The correlated molecular dynamics simulations on the disordered structures show a remarkable enhancement in oxygen diffusivity as compared with ordered pyrochlore lattice and make that a suitable candidate for applications requiring fast oxygen conduction. [ABSTRACT FROM AUTHOR]

Strain is known to greatly influence lowtemperature oxygen electro catalysis on noble metal films, leading to significant enhancements in bifunctional activity essential for fuel cells and metal-air batteries. However, its catalytic impact on transition-metal oxide thin films, such as perovskites, is not widely understood. Here, we epitaxially strain the conducting perovskite LaNi03 to systematically determine its influence on both the oxygen reduction and oxygen evolution reaction. Uniquely, we found that compressive strain could significantly enhance both reactions, yielding a bifunctional catalyst that surpasses the performance of noble metals such as Pt. We attribute the improved bifunctionality to straininduced splitting of the eg orbitals, which can customize orbital asymmetry at the surface. Analogous to straininduced shifts in the d-band center of noble metals relative to the Fermi level, such splitting can dramatically affect catalytic activity in this perovskite and other potentially more active oxides. [ABSTRACT FROM AUTHOR]