67 research outputs found
Crystallographic and magnetic identification of secondary phase in orientated Bi5Fe0.5Co0.5Ti3O15 ceramics
No full textOxide materials which exhibit both ferroelectricity
and ferromagnetism are of great interest for sensors and memory
applications. Layered bismuth titanates with an Aurivillius
structure, (BiFeO3)nBi4Ti3O12, can possess ferroelectric and
ferromagnetic order parameters simultaneously. It has recently
been demonstrated that one such example,
Bi5Fe0.5Co0.5Ti3O15,where n = 1 with half the Fe3+ sites substituted
by Co3+ ions, exhibits both ferroelectric and ferromagnetic
properties at room temperature. Here we report the fabrication
of highly-oriented polycrystalline ceramics of this material,
prepared via molten salt synthesis and uniaxial pressing of high
aspect ratio platelets. Electron backscatter images showed that
there is a secondary phase within the ceramic matrix which is
rich in cobalt and iron, hence this secondary phase could
contribute in the main phase ferromagnetic property. The
concentration of the secondary phase obtained from secondary
electron microscopy is estimated at less than 2.5 %, below the
detection limit of XRD. TEM was used to identify the
crystallographic structure of the secondary phase, which was
shown to be cobalt ferrite, CoFe2O4. It is inferred from the data
that the resultant ferromagnetic response identified using VSM
measurements was due to the presence of the minor secondary
phase. The Remanent magnetization at room temperature was
Mr ≈ 76 memu/g which dropped down to almost zero (Mr ≈ 0.8
memu/g) at 460 oC, far lower than the anticipated for CoFe2O4
Bar constructions for topological operads and the Goodwillie derivatives of the identity
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mathematics, 2005.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Includes bibliographical references (p. 105-106).We describe a cooperad structure on the simplicial bar construction on a reduced operad of based spaces or spectra and, dually, an operad structure on the cobar construction on a cooperad. Further, we show that if the homology of the original operad (respectively, cooperad) is Koszul, then the homology of the bar (respectively, cobar) construction is the Koszul dual. We use our results to construct an operad structure on the partition poset models for the Goodwillie derivatives of the identity functor on based spaces and show that this induces the 'lie' operad structure on the homology groups of these derivatives. Finally, we extend the bar construction to modules over operads (and, dually, to comodules over cooperads) and show that based spaces naturally give rise to modules over the operad formed by the derivatives of the identity.by Michael Ching.Ph.D
Synthesis, Structure and Properties of Pulsed Laser Deposited BiFeO<inf>3</inf>-PbTiO<inf>3</inf> Thin Films
No full textLarge remanent polarization in ferroelectric BiFeO3–PbTiO3 thin films on Pt∕Si substrates
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Combinatorial microfluidic droplet engineering for biomimetic material synthesis
No full textAlthough droplet-based systems are used in a wide range of technologies, opportunities for systematically customizing their interface chemistries remain relatively unexplored. This article describes a new microfluidic strategy for rapidly tailoring emulsion droplet compositions and properties. The approach utilizes a simple platform for screening arrays of droplet-based microfluidic devices and couples this with combinatorial selection of the droplet compositions. Through the application of genetic algorithms over multiple screening rounds, droplets with target properties can be rapidly generated. The potential of this method is demonstrated by creating droplets with enhanced stability, where this is achieved by selecting carrier fluid chemistries that promote titanium dioxide formation at the droplet interfaces. The interface is a mixture of amorphous and crystalline phases, and the resulting composite droplets are biocompatible, supporting in vitro protein expression in their interiors. This general strategy will find widespread application in advancing emulsion properties for use in chemistry, biology, materials and medicine
Maltose and pectin assisted sol–gel production of Ce0.8Gd0.2O1.9 solid electrolyte nanopowders for solid oxide fuel cells
No full textPreparation and properties of tetragonal bismuth ferrite lead titanate thin films using pulsed laser deposition
No full textLowering the centre frequency of thick film PZT devices using acoustically matched backing layers
No full textComparison of Surface and Bulk Crystal Structure in the xBiFeO<inf>3</inf>-(1-x)PbTiO<inf>3</inf> Solid Solution System
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