Enhancing Perovskite Electrocatalysis through Strain Tuning of the Oxygen Deficiency.

Oxygen vacancies in transition-metal oxides facilitate catalysis critical for energy storage and generation. However, promoting vacancies at the lower temperatures required for operation in devices such as metal-air batteries and portable fuel cells has proven elusive. Here we used thin films of perovskite-based strontium cobaltite (SrCoOx) to show that epitaxial strain is a powerful tool for manipulating the oxygen content under conditions consistent with the oxygen evolution reaction, yielding increasingly oxygen-deficient states in an environment where the cobaltite would normally be fully oxidized. The additional oxygen vacancies created through tensile strain enhance the cobaltite's catalytic activity toward this important reaction by over an order of magnitude, equaling that of precious-metal catalysts, including IrO2. Our findings demonstrate that strain in these oxides can dictate the oxygen stoichiometry independent of ambient conditions, allowing unprecedented control over oxygen vacancies essential in catalysis near room temperature.

Enhanced Bifunctional Oxygen Catalysis in Strained LaNiO3 Perovskites.

Strain is known to greatly influence low-temperature oxygen electrocatalysis 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 LaNiO3 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 strain-induced splitting of the eg orbitals, which can customize orbital asymmetry at the surface. Analogous to strain-induced 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.

A policy of omitting an intensive care unit stay after robotic pancreaticoduodenectomy is safe and cost-effective.

BACKGROUND: Immediate postoperative admission to the intensive care unit (ICU) after pancreaticoduodenectomy (PD) is still a standard practice at many institutions. Our aim was to examine whether omission of an immediate postoperative ICU admission would be safe and result in improved outcomes and cost after robotic pancreaticoduodenectomy (RPD). METHODS: In December 2014, a non-ICU admission policy was implemented for patients undergoing RPD. Before this date, all RPDs were routinely admitted to the ICU on post operative day = 0. Using a prospective database, outcomes of the patients in the no-ICU cohort were compared with those of the patients routinely admitted to the ICU before implementation of this policy. RESULTS: The ICU (n = 49) and no-ICU cohorts (n = 47) were comparable in age, gender, body mass index, Charlson comorbidity index and American Society of Anesthesiologists scores, receipt of neoadjuvant therapy, operative time, estimated blood loss, tumor size, and pathologic diagnosis (all P values = NS). Clavien complications, pancreatic leak, reoperation, readmission, and mortality were similar between both the groups (all P values = NS). Hospital length of stay (LOS) was shorter for the no-ICU group (median 6.8 versus 7.7 d, P = 0.01). This reduced LOS and omission of routine postoperative ICU admission translated into a cost reduction from $23,933 (interquartile range $19,833-$28,991) in the ICU group to $19,516 (interquartile range $17,046-$23,893) in the no-ICU group, P = 0.004. The reduction in LOS and cost remained significant after adjusting for all related demographics and perioperative characteristics. CONCLUSIONS: A standard policy of omitting a postoperative ICU admission on post operative day 0 after RPD is safe and can result in reduced LOS and overall savings in total hospital cost.

Strain coupling of oxygen non-stoichiometry in perovskite thin films.

The effects of strain and oxygen vacancies on perovskite thin films have been studied in great detail over the past decades and have been treated separately from each other. While epitaxial strain has been realized as a tuning knob to tailor the functional properties of correlated oxides, oxygen vacancies are usually regarded as undesirable and detrimental. In transition metal oxides, oxygen defects strongly modify the properties and functionalities via changes in oxidation states of the transition metals. However, such coupling is not well understood in epitaxial films, but rather deemed as cumbersome or experimental artifact. Only recently it has been recognized that lattice strain and oxygen non-stoichiometry are strongly correlated in a vast number of perovskite systems and that this coupling can be beneficial for information and energy technologies. Recent experimental and theoretical studies have focused on understanding the correlated phenomena between strain and oxygen vacancies for a wide range of perovskite systems. These correlations not only include the direct relationship between elastic strain and the formation energy of oxygen vacancies, but also comprise highly complex interactions such as strain-induced phase transitions due to oxygen vacancy ordering. Therefore, we aim in this review to give a comprehensive overview on the coupling between strain and oxygen vacancies in perovskite oxides and point out the potential applications of the emergent functionalities strongly coupled to oxygen vacancies.

Spatially Resolved Large Magnetization in Ultrathin BiFeO3.

Here, a quantitative magnetic depth profile across the planar interfaces in BiFeO3 /La0.7 Sr0.3 MnO3 (BFO/LSMO) superlattices using polarized neutron reflectometry is obtained. An enhanced magnetization of 1.83 ± 0.16 µB /Fe in BFO layers is observed when they are interleaved between two manganite layers. The enhanced magnetic order in BFO persists up to 200 K. The depth dependence of magnetic moments in BFO/LSMO superlattices as a function of the BFO layer thickness is also explored. The results show the enhanced net magnetic moment in BFO from the LSMO/BFO interface extends 3-4 unit cells into BFO. The interior part of a thicker BFO layer has a much smaller magnetization, suggesting it still keeps the small canted AFM state. The results exclude charge transfer, intermixing, epitaxial strain, and octahedral rotations/tilts as dominating mechanisms for the large net magnetization in BFO. An explanation-one suggested by others previously and consistent with the observations-attributes the temperature dependence of the net magnetization of BFO to strong orbital hybridization between Fe and Mn across the interfaces. Such orbital reconstruction would establish an upper temperature limit for magnetic ordering of BFO.

Emerging magnetism and anomalous Hall effect in iridate-manganite heterostructures.

Strong Coulomb repulsion and spin-orbit coupling are known to give rise to exotic physical phenomena in transition metal oxides. Initial attempts to investigate systems, where both of these fundamental interactions are comparably strong, such as 3d and 5d complex oxide superlattices, have revealed properties that only slightly differ from the bulk ones of the constituent materials. Here we observe that the interfacial coupling between the 3d antiferromagnetic insulator SrMnO3 and the 5d paramagnetic metal SrIrO3 is enormously strong, yielding an anomalous Hall response as the result of charge transfer driven interfacial ferromagnetism. These findings show that low dimensional spin-orbit entangled 3d-5d interfaces provide an avenue to uncover technologically relevant physical phenomena unattainable in bulk materials.