scholarly journals Near-room temperature ferromagnetic insulating state in highly distorted LaCoO2.5 with CoO5 square pyramids

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qinghua Zhang ◽  
Ang Gao ◽  
Fanqi Meng ◽  
Qiao Jin ◽  
Shan Lin ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Compressive Strain ◽  
High Spin State ◽  
Complex Oxide ◽  
Ferromagnetic State ◽  
Minor Role ◽  
Transmission Electron ◽  
Vacancy Ordering ◽  
Scanning Transmission ◽  
A Minor

AbstractDedicated control of oxygen vacancies is an important route to functionalizing complex oxide films. It is well-known that tensile strain significantly lowers the oxygen vacancy formation energy, whereas compressive strain plays a minor role. Thus, atomic reconstruction by extracting oxygen from a compressive-strained film is challenging. Here we report an unexpected LaCoO2.5 phase with a zigzag-like oxygen vacancy ordering through annealing a compressive-strained LaCoO3 in vacuum. The synergetic tilt and distortion of CoO5 square pyramids with large La and Co shifts are quantified using scanning transmission electron microscopy. The large in-plane expansion of CoO5 square pyramids weaken the crystal field splitting and facilitated the ordered high-spin state of Co2+, which produces an insulating ferromagnetic state with a Curie temperature of ~284 K and a saturation magnetization of ~0.25 μB/Co. These results demonstrate that extracting targeted oxygen from a compressive-strained oxide provides an opportunity for creating unexpected crystal structures and novel functionalities.

scholarly journals Vacancy defect control of colossal thermopower in FeSb2

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Qianheng Du ◽  
Lijun Wu ◽  
Huibo Cao ◽  
Chang-Jong Kang ◽  
Christie Nelson ◽  
...  
Keyword(s):  
Phonon Scattering ◽  
Vacancy Defect ◽  
Electron Microscopic ◽  
First Principle Calculation ◽  
Conducting Path ◽  
Transmission Electron ◽  
Vacancy Ordering ◽  
Defect Control ◽  
Scanning Transmission ◽  
Monoclinic Distortion

AbstractIron diantimonide is a material with the highest known thermoelectric power. By combining scanning transmission electron microscopic study with electronic transport neutron, X-ray scattering, and first principle calculation, we identify atomic defects that control colossal thermopower magnitude and nanoprecipitate clusters with Sb vacancy ordering, which induce additional phonon scattering and substantially reduce thermal conductivity. Defects are found to cause rather weak but important monoclinic distortion of the unit cell Pnnm → Pm. The absence of Sb along [010] for high defect concentration forms conducting path due to Fe d orbital overlap. The connection between atomic defect anisotropy and colossal thermopower in FeSb2 paves the way for the understanding and tailoring of giant thermopower in related materials.

scholarly journals The Interplay between Retinal Pathways of Cholesterol Output and Its Effects on Mouse Retina

Biomolecules ◽  
2019 ◽  
Vol 9 (12) ◽  
pp. 867 ◽  
Author(s):  
Alexey M. Petrov ◽  
Artem A. Astafev ◽  
Natalia Mast ◽  
Aicha Saadane ◽  
Nicole El-Darzi ◽  
...  
Keyword(s):  
Energy Homeostasis ◽  
Cytochromes P450 ◽  
Cholesterol Biosynthesis ◽  
Mouse Retina ◽  
Minor Role ◽  
Compensatory Mechanisms ◽  
Cholesterol Levels ◽  
Transmission Electron ◽  
Retinal Pathways ◽  
A Minor

In mammalian retina, cholesterol excess is mainly metabolized to oxysterols by cytochromes P450 27A1 (CYP27A1) and 46A1 (CYP46A1) or removed on lipoprotein particles containing apolipoprotein E (APOE). In contrast, esterification by sterol-O-acyltransferase 1 (SOAT) plays only a minor role in this process. Accordingly, retinal cholesterol levels are unchanged in Soat1−/− mice but are increased in Cyp27a1−/−Cyp46a1−/− and Apoe−/− mice. Herein, we characterized Cyp27a1−/−Cyp46a1−/−Soat1−/− and Cyp27a1−/−Cyp46a1−/−Apoe−/− mice. In the former, retinal cholesterol levels, anatomical gross structure, and vasculature were normal, yet the electroretinographic responses were impaired. Conversely, in Cyp27a1−/−Cyp46a1−/−Apoe−/− mice, retinal cholesterol levels were increased while anatomical structure and vasculature were unaffected with only male mice showing a decrease in electroretinographic responses. Sterol profiling, qRT-PCR, proteomics, and transmission electron microscopy mapped potential compensatory mechanisms in the Cyp27a1−/−Cyp46a1−/−Soat1−/− and Cyp27a1−/−Cyp46a1−/−Apoe−/− retina. These included decreased cholesterol biosynthesis along with enhanced formation of intra- and extracellular vesicles, possibly a reserve mechanism for lowering retinal cholesterol. In addition, there was altered abundance of proteins in Cyp27a1−/−Cyp46a1−/−Soat1−/− mice that can affect photoreceptor function, survival, and retinal energy homeostasis (glucose and fatty acid metabolism). Therefore, the levels of retinal cholesterol do not seem to predict retinal abnormalities, and it is rather the network of compensatory mechanisms that appears to determine retinal phenotype.

scholarly journals HR-TEM study of oxygen vacancy ordered Sr4+nMn4+nO10+3n compounds

2014 ◽  
Vol 70 (a1) ◽  
pp. C942-C942
Author(s):  
Leopoldo Suescun ◽  
Joke Hadermann ◽  
Bogdan Dabrowski
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Oxygen Vacancy ◽  
Oxygen Vacancies ◽  
Specific Pattern ◽  
Orbital Ordering ◽  
Rich Region ◽  
Transmission Electron ◽  
Vacancy Ordering

The study of oxygen vacancy ordering in the LaxSr1-xMnOy system has shown a strong correlation between Mn formal valence and coordination to oxygen. The Mn2+ was found forming octahedra (Oc) and tetrahedra (Te), Mn3+ octahedra and pyramids (Py) and Mn4+ only octahedra. This tendency was derived from the presence of three kinds of vacancy orderings in the system. For y>2.5 and the average Mnm+ charge of 2<m<3 (x>0.5), brownmillerite-type structures are found with Mn2+/3+ Oc and Mn2+ Te. [1] For 3<m<4 (x<0.5) structures of the homologous Sr4+nMn4+nO10+3n –type series are found with Mn3+ Py and Mn3+/4+ Oc. [2] For y<2.5 and 2<m<3 (x<0.5) a complex layered structure with OcTeOcOcTe'Oc ordering and step defects of Mn3+ Py and Mn2+ Te [3] is observed. Brownmillerite-type structure is absent in the Sr-rich region since mostly Mn3+ is present, which does not show tendency to form Te. Compounds of the Sr4+nMn4+nO10+3n series have been described as arrangements of groups of four Py and n Oc in symmetrical patterns. [2] This description did not elucidate the crystal chemistry reasons for specific pattern (n=0, 1 and 3) since it neglected the coordination stabilization associated with oxygen vacancy, charge and orbital ordering observed in the structures.[2] Using high-resolution transmission electron microscopy (HR-TEM) for SrMnOy with y values located between corresponding n=0, 1 and 3 compositions, we have determined that the oxygen vacancy ordering directs the formation of these patterns. The structural patterns can be described as perovskites with lines of oxygen vacancies along [001] with nearest lines of vacancies in the cubic (310) plane. Successive (310) planes are n perovskite blocks (Oc) apart in the [010] direction. This ordering pattern allows the coherent growth of phases with different n at the sides of (310) plane as observed in grains of a sample of SrMnO2.668 where n=1 and n=3 phases grown coherently one at each side of the vacancy plane.

scholarly journals Analysis of Benzene-Induced Effects onRhodococcussp. 33 Reveals that Constitutive Processes Play a Major Role in Conferring Tolerance

2009 ◽  
Vol 9 ◽  
pp. 209-223 ◽  
Author(s):  
Tony Gutiérrez ◽  
Robert Learmonth ◽  
Iain Couperwhite
Keyword(s):  
Cell Membrane ◽  
Degradation Pathway ◽  
Minor Role ◽  
Adaptive Responses ◽  
Benzene Degradation ◽  
Liquid Benzene ◽  
Transmission Electron ◽  
High Concentrations ◽  
Solvent Tolerant ◽  
A Minor

Most studies investigating mechanisms that confer microorganisms with tolerance to solvents have often focused on adaptive responses following exposure, while less attention has been given to inherent, or constitutive, processes that prevail at the onset of exposure to a toxic solvent. In this study, we investigated several properties of the highly solvent-tolerant bacteriumRhodococcussp. 33 that confer it with a tolerance to high concentrations of benzene. When challenged with liquid benzene, the growth of both nonadapted and adapted cells was decreased by 0.25¨C0.30% (v/v) liquid benzene, and higher concentrations (≤0.35% v/v) produced a complete cessation in the growth of only nonadapted cells. When exposed to presolubilized benzene, nonadapted cells tolerated ≥1000 mg/l, whereas adapted cells tolerated >1400 mg/l. Measuring the cell membrane fluidity of the cells during these exposure experiments showed that at the onset of exposure, the membranes of adapted cells were less affected by benzene compared to nonadapted cells, although these effects were insignificant in the long term. Several benzene-sensitive mutants were generated from thisRhodococcus, two of which were unable to degrade benzene, yet they still tolerated 500¨C800 mg/l. This confirmed our earlier work suggesting that the benzene-degradation pathway of this organism plays a minor role in tolerance. Under the phase and transmission electron microscope, the mutants were found to have lost the ability to produce extracellular polymers, and many cells appeared pleomorphic, containing intracellular membrane invaginations and mesosome-like structures. As will be discussed, these results identify important functions of the cell membrane, the cell wall, and extracellular polymer in their native state (i.e., before exposure) in conferring this organism with tolerance to benzene.

scholarly journals The Relationship between the Morphology and Structure and the Quality of Fruits of Two Pear Cultivars (Pyrus communisL.) during Their Development and Maturation

2013 ◽  
Vol 2013 ◽  
pp. 1-13 ◽  
Author(s):  
Agata Konarska
Keyword(s):  
Fruit Quality ◽  
Fruit Set ◽  
Minor Role ◽  
Maturity Stage ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
A Minor ◽  
Harvest Maturity

The flavour and nutritional values of pears are appreciated by consumers worldwide, who, however, demand specific fruit quality, that is, attractive appearance, firmness and flavour, and health safety as well as long-term shelf life and storability. Pear cultivars differ in terms of the above-mentioned traits; therefore, we undertook investigations to demonstrate the differences in structure of fruits of two pear cultivars that determine fruit quality in its broadest sense. The micromorphology, anatomy, and ultrastructure of “Clapp’s Favourite” and “Conference” fruits in the fruit set stage and in the harvest maturity stage were investigated under light microscope and scanning and transmission electron microscopes. The fruits of “Clapp’s Favourite” and “Conference” in the fruit set stage exhibited distinct differences in the values of anatomical parameters only. Substantial differences in fruit structure were observed in the harvest maturity stage. The analyses indicate that firmness and durability of pear fruits are largely influenced by the presence of russeting, the proportion of closed lenticels and number of stone cells, and the content of starch grains and tannin compounds. The thickness of the cuticle and presence of epicuticular waxes as well as the number of lenticels and the number and depth of microcracks play a minor role.

scholarly journals Oxygen vacancy-induced topological nanodomains in ultrathin ferroelectric films

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Wei Peng ◽  
Junsik Mun ◽  
Qidong Xie ◽  
Jingsheng Chen ◽  
Lingfei Wang ◽  
...  
Keyword(s):  
Oxygen Vacancy ◽  
Electric Fields ◽  
Oxygen Vacancies ◽  
Local Strain ◽  
Strongly Coupled ◽  
Polar Order ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electric Dipoles ◽  
Uniaxial Ferroelectric

AbstractOxygen vacancy in oxide ferroelectrics can be strongly coupled to the polar order via local strain and electric fields, thus holding the capability of producing and stabilizing exotic polarization patterns. However, despite intense theoretical studies, an explicit microscopic picture to correlate the polarization pattern and the distribution of oxygen vacancies remains absent in experiments. Here we show that in a high-quality, uniaxial ferroelectric system, i.e., compressively strained BaTiO3 ultrathin films (below 10 nm), nanoscale polarization structures can be created by intentionally introducing oxygen vacancies in the film while maintaining structure integrity (namely no extended lattice defects). Using scanning transmission electron microscopy, we reveal that the nanodomain is composed of swirling electric dipoles in the vicinity of clustered oxygen vacancies. This finding opens a new path toward the creation and understanding of the long-sought topological polar objects such as vortices and skyrmions.

The High Resolution Scanning Transmission Electron Microscope

1974 ◽  
Vol 32 ◽  
pp. 316-317
Author(s):  
A. V. Crewe
Keyword(s):  
Electron Microscope ◽  
High Resolution ◽  
High Vacuum ◽  
Scanning Transmission Electron Microscope ◽  
Ultra High Vacuum ◽  
Resolving Power ◽  
Imaging Characteristics ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
The Moment

The high resolution STEM is now a fact of life. I think that we have, in the last few years, demonstrated that this instrument is capable of the same resolving power as a CEM but is sufficiently different in its imaging characteristics to offer some real advantages.It seems possible to prove in a quite general way that only a field emission source can give adequate intensity for the highest resolution^ and at the moment this means operating at ultra high vacuum levels. Our experience, however, is that neither the source nor the vacuum are difficult to manage and indeed are simpler than many other systems and substantially trouble-free.

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