On stoichiometry and intermixing at the spinel/perovskite interface in CoFe2O4/BaTiO3 thin films

The performance of complex oxide heterostructures depends primarily on the interfacial coupling of the two component structures. This interface character inherently varies with the synthesis method and conditions used since even small composition variations can alter the electronic, ferroelectric, or magnetic functional properties of the system. The focus of this article is placed on the interface character of a pulsed laser deposited CoFe2O4/BaTiO3 thin film. Using a range of state-of-the-art transmission electron microscopy methodologies, the roles of substrate morphology, interface stoichiometry, and cation intermixing are determined on the atomic level. The results reveal a surprisingly uneven BaTiO3 substrate surface formed after the film deposition and Fe atom incorporation in the top few monolayers inside the unit cell of the BaTiO3 crystal. Towards the CoFe2O4 side, a disordered region extending several nanometers from the interface was revealed and both Ba and Ti from the substrate were found to diffuse into the spinel layer. The analysis also shows that within this somehow incompatible composite interface, a different phase is formed corresponding to the compound Ba2Fe3Ti5O15, which belongs to the ilmenite crystal structure of FeTiO3 type. The results suggest a chemical activity between these two oxides, which could lead to the synthesis of complex engineered interfaces

First-principles characterization of Mg low-index surfaces: Structure, reconstructions, and surface core-level shifts

In this paper, first-principles calculations provide structural characterization of three low-index Mg surfaces - Mg(0001), Mg(1010), and Mg(1120) - and their respective surface core-level shifts (SCLSs). Inspired by the close similarities between Be and Mg surfaces, we also explore the reconstruction of Mg(1120). Through the calculation of surface energies and the use of the angular-component decomposed density of states, we show that reconstructions are likely to occur at the Mg(1120) surface, similarly to what was found earlier for Be(1120). Indeed, the surface energy of some of the explored reconstructions is slightly lower than that of the unreconstructed surface. In addition, because of lattice symmetry, the morphology of the unreconstructed surface (1120) results in a steplike zig-zag chain packing, with topmost chains supporting a resonant, quasi-one-dimensional (1D), partially filled electronic state. As the presence of partially filled quasi-1D bands is a necessary condition for Peierls-like dimerization, we verify that the undimerized surface chain remains stable with respect to it. Some of the reconstructions, namely, the 2 71 and 3 71 added row reconstructions, induce a stronger relaxation of the topmost chains, increasing the coupling with lower layers and thus significantly damping the quasi-1D character of this state. The original approach followed offers a common and general framework to identify quasi-1D bands - even in the case of resonant electronic surface states - and to meaningfully compare calculated and measured SCLSs even in the presence of multicomponent peak contributions

Chemodiversity of Exudate Flavonoids in Seven Tribes of Cichorioideae and Asteroideae (Asteraceae) §

Members of several genera of Asteraceae, belonging to the tribes Mutisieae, Cardueae, Lactuceae (all subfamily Cichorioideae), and of Astereae, Senecioneae, Helenieae and Heliantheae (all subfamily Asteroideae) have been analyzed for chemodiversity of their exudate flavonoid profiles. The majority of structures found were flavones and flavonols, sometimes with 6-and/or 8-substitution, and with a varying degree of oxidation and methylation. Flavanones were observed in exudates of some genera, and, in some cases, also flavonol-and flavone glycosides were detected. This was mostly the case when exudates were poor both in yield and chemical complexity. Structurally diverse profiles are found particularly within Astereae and Heliantheae. The tribes in the subfamily Cichorioideae exhibited less complex flavonoid profiles. Current results are compared to literature data, and botanical information is included on the studied taxa

An overview of R&D work in friction stir welding at SMU

Friction stir welding (FSW) is an innovative solid-state material joining method invented by The Welding Institute (TWI) in 1991 and has been one of the most significant joining technology developments in the last two decades. It has evolved into a process focused on joining arc weldable (5xxx and 6xxx) and unweldable (2xxx and 7xxx) aluminum alloys to a point where it can be implemented by the aerospace and automotive industries for their joining needs.Research towards the further extension of the process to join dissimilar metal combinations like Fe-Al and Al-Cu is currently underway. A few of the important advantages of FSW over conventional joining techniques include improved joint properties and performance, low-deformation of the workpieces, a significant reduction in production costs and the freeing of skilled labor for use in other tasks. Compared to the conventional arc-welding of aluminum alloys, FSW produces a smaller heat affected zone, and it also allows the successful joining of aluminum alloys, steel, titanium, and dissimilar alloys with a stronger joint

Collective dipole effects in ionic transport under electric fields

In the context of ionic transport in solids, the variation of a migration barrier height under electric fields is traditionally assumed to be equal to the classical electric work of a point charge that carries the transport charge. However, how reliable is this phenomenological model and how does it fare with respect to Modern Theory of Polarization? In this work, we show that such a classical picture does not hold in general as collective dipole effects may be critical. Such effects are unraveled by an appropriate polarization decomposition and by an expression that we derive, which defines the equivalent polarization-work charge. The equivalent polarization-work charge is not equal neither to the transported charge, nor to the Born effective charge of the migrating atom alone, but it is defined by the total polarization change at the transition state. Our findings are illustrated by oxygen charged defects in MgO and in SiO2

v-P 2 O 5 micro-clustering in P-doped silica studied by a first-principles Raman investigation

Synthetic vitreous silica is currently the preferred material for the production of optical fibres because of the several excellent properties of this glass, e.g. high transmission in the visible and IR domains, high mechanical strength, chemical durability, and ease of doping with various materials. For instance, fiber lasers and amplifiers exploit the light amplification properties provided by rare-earth ions employed as dopants in the core of silica-based optical fibers. The structure and composition of the nearest neighbor shell surrounding rare-earth ions in silica-based optical fibers and amplifiers have been intensively debated in the last decade. To reduce aggregation effects between rare-earth ions, co-dopants such as phosphorus and aluminium are added as structural modifiers; phosphorus-doping, in particular, has proved to be very efficient in dissolving rare-earth ions. In this work, we provide further insights concerning the embedding of P atoms into the silica network, which may be relevant for explaining the ease of formation of a phosphorus pentoxide nearest-neighbor shell around a rare-earth dopant. In particular, by means of first-principles calculations, we discuss alternative models for an irradiation (UV, x\u2013, \u3b3-rays) induced paramagnetic center, i.e. the so called room-temperature phosphorus-oxygen-hole center, and its precursors. We report that the most likely precursor of a room-temperature phosphorus-oxygen-hole center comprises of a micro-cluster of a few (at least two) neighboring phosphate tetrahedra, and correspondingly that the occurrence of isolated [(O-) 2 P(=O) 2 ] 12 units is unlikely even at low P-doping concentrations. In fact, this work predicts that the symmetric stretching of P=O bonds in isolated [(O-) 2 P(=O) 2 ] 12 units appears as a Raman band at a frequency of ~1110 cm 121 , and only by including at least another corner-sharing phosphate tetrahedron, it is shown to shift to higher frequencies (up to ~40 cm 121 ) due to the shortening of P=O bonds, thereby leading to an improved agreement with the observed Raman band located at ~1145 cm 121

Thermoplastic Green Machining for Textured Dielectric Substrate for Broadband Miniature Antenna

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/65902/1/j.1551-2916.2005.00089.x.pd

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC