Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session Y5: New Functionalities in Glasses and Nanomaterials |
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Sponsoring Units: FIAP Chair: Punit Boolchand, University of Cincinatti Room: Baltimore Convention Center 309 |
Friday, March 17, 2006 8:00AM - 8:36AM |
Y5.00001: Glasses and Ceramics as Templates for Generating Nanostructures and Novel Properties Invited Speaker: Silica glasses containing substantial amounts of modifying oxides have considerable void spaces within their structure . These systems have therefore been exploited to generate different kinds of nanostructures e.g., nanoparticles,core-shell structures and nanowires. Similarly, ceramic structure like mica have well-defined crystal channels. The latter have been used to prepare nanowires or nanosheets. In this lecture the author will discuss some examples in which the above strategies of material synthesis have been applied. Copper core-copper oxide shell nanostructures with diameters $\sim$6 nm were grown within a gel-derived silicate glass containing copper ions$^{1}$. Electrical conductivity of the nanocomposites was several orders of magnitude higher than that of the parent glass. An interfacial amorphous phase gave rise to this behaviour. Electrical conduction was ascribed to a small polaron hopping mechanism. Silver metal core--silver oxide shell structure with nanometer dimensions were generated in a silicate glass by first precipitating silver particles of $\sim$ 6nm diameter by an electrodeposition process and subsequently subjecting the material to an oxidation treatment$^{2}$. Detailed analysis of the optical absorption spectra led to the conclusion that there is a metal non metal transition for particles having diameters less than $\sim$ 2.5 nm. Similar results were obtained in the case of copper core- copper oxide shell nanostructures grown within a silicate glass$^{3}$. Core-shell structure of Fe-Fe$_{3}$O$_{4}$ system was also produced within a gel derived silica glass which exhibited a four order of magnitude change in electrical resistivity when the relative humidity was changed from 25{\%}to 95{\%} $^{4}$. Silver and copper nanowires respectively were grown within a silicate glass by the application of an electric field. These nanowires were found to consist of arrays of metal nanoparticles. The latter gave rise to nano-junctions between large and small particles which behaved as metal--semiconductor junctions. A diode like voltage current characteristic was observed in these nanocomposites.$^{5}$ Silver nanowires were grown by electrodeposition within gel--derived silica glasses containing pores having diameters in the nanometre range. After suitable treatment to these nanowires these exhibited single electron tunnelling property$^{6}$. Silver nanowires were grown within the channels of fluorophlogopite mica crystals precipitated within a suitably chosen glass composition. The nanocomposites exhibited giant dielectric permittivity ($\sim$10$^{7}$) which were explained on the basis of Gorkov-Eliashberg and Rice--Bernasconi model$^{7}$. Na-4mica structure was used to grow CdS nanowire$^{8}$. The former was also used to prepare films of BaTiO$_{3}$ with a thickness of 1.2 nm. These films did not show any ferroelectric behaviour which was consistent with recent theoretical prediction$^{9}$. [1] D.Das and D.Chakravorty , Appl. Phys. Lett. \underline {76}, 1273 (2000). [2] K.Chatterjee,S.Banerjee and D . Chakravorty, Phys. Rev. B\underline {66}, 085421 (2002). [3] K.Chatterjee, D.Das and D.Chakravorty, J.Phys .D : Appl. Phys. \underline {38} 451 (2005) [4] B.N.Pal ,S.Basuand D.Chakravorty, J. Appl. Phys. \underline {97}, 034311 (2005). [5] A.Dan,B.Satpati,P. V.Satyam and D.Chakravorty, J.Appl. Phys. \underline {93}, 4794 (2003). [6] S.Bhattacharyya,S.K.Saha and D.Chakravorty, Appl. Phys. Lett. \underline {77,} 3770 (2000). [7] P.K.Mukherjee and D.Chakravorty, J. Mater. Res. \underline {17} 3127 (2002). [8] P.K.Mukherjee and D.Chakravorty, J. Appl. Phys. \underline {95,} 3164 (2004). A.Dan,P.K.Mukherjee and D.Chakravorty, J. Mater. Chemistry \underline {15,} 1477 (2005).. [Preview Abstract] |
Friday, March 17, 2006 8:36AM - 9:12AM |
Y5.00002: Local structure and dynamics of ferroelectric domain walls in perovskite oxides Invited Speaker: |
Friday, March 17, 2006 9:12AM - 9:48AM |
Y5.00003: Novel polarization dependent photoinduced effects in glass Invited Speaker: For centuries oxide glasses have been used successfully in windows, thus indicating that they remain stable, unlike plastics, against exposure to sunlight. By comparison, the structure and properties of closely related chalcogenide glasses are easily altered by exposure to visible light of energy $\ge $ bandgap of the material. In general, such photoinduced changes may be classified into three categories depending on their stability: (a) permanent changes which cannot be recovered unless the sample is melted and prepared again, (b) metastable changes which can be reversed by heating the sample to the glass transition temperature, and (c) temporary changes which can be reversed simply by removing the light source, or exposing the specimen to another appropriate light subsequently. Among the numerous photoinduced phenomena, the photoinduced vector effects like anisotropic light transmission, mass transport, opto-mechanical effect, etc. are particularly fascinating as they depend on the direction of light polarization in spite of the isotropic glass structure. The transient `vector' optical effects, which are produced by linearly polarized light and then erased by either unpolarized or circularly polarized light, are even more intriguing and novel. This paper will review the various observations of photoinduced vector effects. It will then focus on the origin of such effects, which we have sought by probing the changes in atomic and electronic structure under in situ laser irradiation. [Preview Abstract] |
Friday, March 17, 2006 9:48AM - 10:24AM |
Y5.00004: Polyamorphic transitions in network glasses and glass-forming liquids Invited Speaker: Over the past two decades, we have witnessed increasing evidence for the occurrence of polyamorphism, i.e., the existence of more than one thermodynamically and structurally distinct non-crystalline state of a given substance. This concept is manifest predominantly through the transitions between different polyamorphic states, as we are still not able to unequivocally describe a given amorphous structure. However, if substantiated, the concept of polyamorphism should facilitate such a description, since it implies that polyamorphic states are uniquely defined and a distinctive structural character must exist for each state. We have observed polyamorphic transitions in a number of glass-forming systems, e.g., when probing their high-frequency visco-elastic response as a function of temperature,[1] or when compacting such systems at high pressures. We have carried out molecular dynamics simulations to reveal explanations for the phenomena observed in experiments.[2] In this presentation we discuss reversible and irreversible transitions in silica glass, their relation to the anomalous thermo-mechanical properties of this material, and the effects of permanent densification on structure and properties. We present an unusual transition in boron oxide glass, which is continuous upon compression and discontinuous upon decompression.[3] We show how the manifestations of polyamorphic transitions and their are related to structural transformations in the crystalline counterparts of these materials, and how this can even lead to the discovery of previously unknown metastable crystalline phases. [1] J. Kieffer, J.E. Masnik, O. Nickolayev, and J.D. Bass, Phys. Rev. B \textbf{58}, 694 (1998). [2] L. Huang, and J. Kieffer, Phys. Rev. B \textbf{69}, 224203 and 224204 (2004). [3] J.D. Nicholas, S.V. Sinogeikin, J. Kieffer, and J.D. Bass, Phys. Rev. Letters \textbf{92}, 215701 (2004). [Preview Abstract] |
Friday, March 17, 2006 10:24AM - 11:00AM |
Y5.00005: Nanoscale glass for photonic applications Invited Speaker: |
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