The complex correlation between Mn3+ ions and the disordered phase in the lattice structure of high voltage spinel, and its effect on the charge transport properties, are revealed through a ...combination of experimental study and computer simulations. Superior cycling stability is achieved in LiNi0.45Cr0.05Mn1.5O4 with carefully controlled Mn3+ concentration. At 250th cycle, capacity retention is 99.6% along with excellent rate capabilities.
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•Steroid substrates modulate the interaction of three mitochondrial CYPs with common redox-partner.•Steroids action is isoform-specific: parameters of CYP11A1 – Adx and CYP11B – Adx ...complexes are affected differently.•Intermediates of the multistep reactions, catalyzed by CYP11A1 and CYP11B2 also modulate protein-protein interactions.
Steroidogenesis is strictly regulated at multiple levels, as produced steroid hormones are crucial to maintain physiological functions. Cytochrome P450 enzymes are key players in adrenal steroid hormone biosynthesis and function within short redox-chains in mitochondria and endoplasmic reticulum. However, mechanisms regulating supply of reducing equivalents in the mitochondrial CYP-dependent system are not fully understood. In the present work, we aimed to estimate how the specific steroids, substrates, intermediates and products of multistep reactions modulate protein-protein interactions between adrenodoxin (Adx) and mitochondrial CYP11 s. Using the SPR technology we determined that steroid substrates affect affinity and stability of CYP11s–Adx complexes in an isoform-specific mode. In particular, cholesterol induces a 4-fold increase in the rate of CYP11A1 – Adx complex formation without significant effect on dissociation (koff decreased ∼1.5-fold), overall increasing complex affinity. At the same time steroid substrates decrease the affinity of both CYP11B1 – Adx and CYP11B2 – Adx complexes, predominantly reducing their stability (4–7 fold). This finding reveals differentiation of protein-protein interactions within the mitochondrial pool of CYPs, which have the same electron donor. The regulation of electron supply by the substrates might affect the overall steroid hormones production. Our experimental data provide further insight into protein-protein interactions within CYP-dependent redox chains involved in steroidogenesis.
The response of the microbial community (microbial biomass carbon (C
mic
), basal respiration (BR), and functional diversity (FD)) of agrosoddy-podzolic soil (Albic Glossic Retisols (Loamic, Aric ...Cutanic, Ochric)) to pollution by heavy metals (HMs: Cu 660, Zn 1100, Pb 650 mg/kg) and carbon-containing preparations (5% of biochar and 0.25% of lignohumate) was studied in model experiment (30 days). Soils with different organic carbon contents (C
org
3.86 and 1.30%) were sampled at two sites (Chashnikovo, Moscow oblast). We determined C
mic
by the substrate-induced respiration method and FD by multisubstrate testing (47 substrates). It was found that HMs application reduced C
mic
on average by 49–57%, BR by 23–52%, and FD by 45%, but, on the contrary, increased the microbial metabolic quotient (
q
CO
2
= BR/C
mic
) by 9–46%. The changes of these properties were most significant in the soil with low C
org
content (1.30%). Carbon-containing preparations did not contribute to variations in C
mic
, BR, and
q
CO
2
in both soils with HMs, but increased their FD. It is concluded that the studied microbiological parameters may be used as indicators for optimal assessment of soil quality: FD and C
mic
are the more sensitive to HMs than BR and
q
CO
2
.
Interfacial intermixing and electronic structure were investigated at thin (3–5 unit cells.), epitaxial La1-xAl1+xO3/SrTiO3(001) heterojunctions for x = 0 and ± 0.05. Angle-resolved X-ray ...photoelectron spectroscopy reveals rather extensive cation intermixing for all films, independent of composition. The valence band offset for the nominally stoichiometric (x = 0) film is 0.16 ± 0.10 eV, with the valence band maximum of SrTiO3 being deeper in binding energy than that of LaAlO3. Similar values are obtained for x = ± 0.05. There is no measurable band bending in either the LaAlO3 or the SrTiO3 near the interface. These results are at odds with first principles theoretical predictions based on perfect stoichiometry and an abrupt interface model. Finally, however, inclusion of intermixing in the compositional description of the interface results in successful prediction of the valence band offset and absence of band bending.
Oxygen vacancies are often present in complex oxides as point defects, and their effect on the electronic properties is typically uniform and isotropic. Exploiting oxygen deficiency in order to ...generate controllably novel structures and functional properties remains a challenging goal. Here we show that epitaxial strontium chromite films can be transformed, reversibly and at low temperature, from rhombohedral, semiconducting SrCrO(2.8) to cubic, metallic perovskite SrCrO(3-δ). Oxygen vacancies in SrCrO(2.8) aggregate and give rise to ordered arrays of {111}-oriented SrO(2) planes interleaved between layers of tetrahedrally coordinated Cr(4+) and separated by ~1 nm. First-principle calculations provide insight into the origin of the stability of such nanostructures and, consistent with the experimental data, predict that the barrier for O(2-) diffusion along these quasi-two-dimensional nanostructures is significantly lower than that in cubic SrCrO(3-δ). This property is of considerable relevance to solid oxide fuel cells in which fast O(2-) diffusion reduces the required operating temperature.
We present the results of calculations of the energy levels of defects at the (001) surface of MgO relative to the top of the valence band and values of defect ionisation potentials and electron ...affinities. The calculations were made using an embedded cluster method in which a cluster of several tens of ions treated quantum mechanically is embedded in a finite array of polarisable and point ions modelling the crystalline potential and the classical polarisation of the host lattice. The calculated ionisation potential of the ideal surface, which fixes the position of the top of the valence band with respect to the vacuum level, is about 6.7
eV. This value is used as a reference for positioning the energy levels of three charge states of a surface anion vacancy, which are also calculated as ionisation energies with respect to the vacuum level. The surface and vacancy electron affinities are calculated using the same method. As a prototype low-coordinated surface site, we have considered a cube corner. Our calculations predict the splitting of the corner states from the top of the surface valence band by about 1.0
eV. Both unrelaxed and relaxed holes are strongly localised at the corner oxygen ion. The ionisation energies and electron affinities of the corner anion vacancy are calculated. The electrons in the F and F
+ centres at the corner are shown to be significantly delocalised over surrounding Mg ions.
The question of stability against diffusional mixing at the prototypical LaAlO3/SrTiO3(001) interface is explored using a multi-faceted experimental and theoretical approach. We combine analytical ...methods with a range of sensitivities to elemental concentrations and spatial separations to investigate interfaces grown using onaxis pulsed laser deposition. We also employ computational modeling based on the density function theory as well as classical force fields to explore the energetic stability of a wide variety of intermixed atomic configurations relative to the idealized, atomically abrupt model. Statistical analysis of the calculated energies for the various configurations is used to elucidate the relative thermodynamic stability of intermixed and abrupt configurations. We find that on both experimental and theoretical fronts, the tendency toward intermixing is very strong. We have also measured and calculated key electronic properties such as potential energy gradients and valence band discontinuity at the interface. We find no measurable electric field in either the LaAlO3 or SrTiO3, and that the valence band offset is near zero, partitioning the band discontinuity almost entirely to the conduction band edge. Significantly, we find it is not possible to account for these electronic properties theoretically without including extensive intermixing in our physical model of the interface. The atomic configurations which give the greatest electrostatic stability are those that eliminate the interface dipole by intermixing, calling into question the conventional explanation for conductivity at this interface – electronic reconstruction. Rather, evidence is presented for La indiffusion and doping of the SrTiO3 below the interface as being the cause of the observed conductivity.
We combine state-of-the-art oxide epitaxial growth by hybrid molecular beam epitaxy with transport, x-ray photoemission, and surface diffraction, along with classical and first-principles quantum ...mechanical modeling to investigate the nuances of insulating layer formation in otherwise high-mobility homoepitaxial n-SrTiO3(001) films. Our analysis points to charge immobilization at the buried n-SrTiO3/undoped SrTiO3(001) interface as well as within the surface contamination layer resulting from air exposure as the drivers of electronic dead-layer formation. As Fermi level equilibration occurs at the surface and the buried interface, charge trapping reduces the sheet carrier density (n2D) and renders the n-STO film insulating if n2D falls below the critical value for the metal-to-insulator transition.
The ability to design and fabricate electronic devices with reproducible properties using complex oxides is critically dependent on our ability to controllably synthesize these materials in thin‐film ...form. Structure‐property relationships are intimately tied to film and interface composition. Here the effect of cation stoichiometry on structural quality and defect formation in LaCrO3 heteroepitaxial films prepared using molecular beam epitaxy is reported. From first principles the regions of stability of various candidate defects, along with the predicted effects of these defects on structural parameters, are calculated as a function of Cr and O chemical potential. Epitaxial LaCrO3 films readily nucleate and remain coherently strained on SrTiO3(001) over a wide range of La‐to‐Cr atom ratios, but La‐rich films are of considerably lower structural quality than stoichiometric and Cr‐rich films. Cation imbalances are accompanied by anti‐site defect formation. Cation mixing occurs at the interface for all La‐to‐Cr ratios investigated and is not quenched by deposition on SrTiO3(001) at ambient temperature. Indiffused La atoms occupy Sr sites. Intermixing is effectively quenched by using molecular beam epitaxy to deposit LaCrO3 at ambient temperature on defect free Si(001). However, analogous pulsed laser deposition on Si is accompanied by cation mixing.
The effect of cation stoichiometry and substrate defect density on nucleation, structure, defect formation, and interfacial mixing during III‐III perovskite complex oxide heteroepitaxy is explored. Cation imbalance is shown to result in anti‐site defect formation within the film, and subsurface cation vacancies promote cation mixing.
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