Scholarly Works, Physics

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https://hdl.handle.net/10919/24287
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Browsing Scholarly Works, Physics by Department "Materials Science and Engineering"

Now showing 1 - 6 of 6
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    Evidence of decoupled lattice distortion and ferroelectric polarization in the relaxor system PMN-xPT
    Xu, Guangyong; Viehland, Dwight D.; Li, Jiefang; Gehring, Peter M.; Shirane, Gen (American Physical Society, 2003-12-30)
    We report high q-resolution neutron scattering data on PMN-xPT single crystals with x=20% and 27%. No rhombohedral distortion occurs in the 20PT sample for temperatures as low as 50 K. On the other hand, the 27PT sample transforms into a rhombohedral phase below T(C)similar to375 K. Our data provide conclusive evidence that a phase with an average cubic lattice is present in the bulk of this relaxor system at low PT concentration, in which the ferroelectric polarization and lattice distortion are decoupled. The rhombohedral distortion is limited to the outermost tens of microns of the crystal.
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    Infrared activity in the Aurivillius layered ferroelectric SrBi2Ta2O9
    Moret, M. P.; Zallen, Richard H.; Newnham, R. E.; Joshi, Pooran C.; Desu, Seshu B. (American Physical Society, 1998-03-01)
    Experimental studies were carried out on infrared-active phonons in the Aurivillius ferroelectric SrBi2Ta2O9 (SBT), using reflectivity measurements (down to 200 cm(-1)) and transmission measurements (down to 100 cm(-1)) on crystals, pellets, and thin films. An analysis was done of the contrasting consequences of the competing orthorhombic and pseudotetragonal symmetries in SBT. Reflectivity results for light polarized in the ab plane show that the anisotropy in this plane is small in the frequency range from 300 to 1200 cm(-1),, indicating the influence of the approximate tetragonal symmetry. Dielectric dispersion properties were derived for this polarization (E perpendicular to c) in this frequency range. The transverse-optical (TO) and longitudinal-optical (LO) frequencies corresponding to the dominant E perpendicular to c band are 613 and 773 cm(-1), respectively. This strong, high-frequency band arises from a mode dominated by the motion of the oxygen sublattice; its TO and LO frequencies yield an oxygen-ion Szigeti effective charge of -1.5e. Frequency estimates for the TO (LO) pairs of other strong bands are 188(330) and 334(451) cm(-1) for E perpendicular to c, and 610(675) and 780(815) cm(-1) for E parallel to c. In addition to the main infrared bands, the main Raman bands of SBT are also reported.
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    Ion transport and storage of ionic liquids in ionic polymer conductor network composites
    Liu, Yang; Liu, Sheng; Lin, Junhong; Wang, Dong; Jain, Vaibhav; Montazami, Reza; Heflin, James R.; Li, Jing; Madsen, Louis A.; Zhang, Q. M. (AIP Publishing, 2010-05-01)
    We investigate ion transport and storage of ionic liquids in ionic polymer conductor network composite electroactive devices. Specifically, we show that by combining the time domain electric and electromechanical responses, one can gain quantitative information on transport behavior of the two mobile ions in ionic liquids (i.e., cation and anion) in these electroactive devices. By employing a two carrier model, the total excess ions stored and strains generated by the cations and anions, and their transport times in the nanocomposites can be determined, which all depend critically on the morphologies of the conductor network nanocomposites. (C) 2010 American Institute of Physics. [doi:10.1063/1.3432664]
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    Layer-by-layer self-assembled conductor network composites in ionic polymer metal composite actuators with high strain response
    Liu, S.; Montazami, Reza; Liu, Y.; Jain, V.; Lin, M. R.; Heflin, James R.; Zhang, Q. M. (AIP Publishing, 2009-07-01)
    We investigate the electromechanical response of conductor network composite (CNC) fabricated by the layer-by-layer (LbL) self-assembly method. The process makes it possible for CNCs to be fabricated at submicron thickness with high precision and quality. This CNCs exhibits high strain similar to 6.8% under 4 V, whereas the RuO(2)/Nafion CNCs exhibit strain similar to 3.3%. The high strain and submicron thickness of the LbL layers in an ionic polymer metal composite (IPMC) yield large and fast actuation. The response time of a 26 mu m thick IPMC with 0.4 mu m thick LbL CNCs to step voltage of 4 V is 0.18 s.
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    Millisecond switching in solid state electrochromic polymer devices fabricated from ionic self-assembled multilayers
    Jain, V.; Yochum, H. M.; Montazami, Reza; Heflin, James R. (AIP Publishing, 2008-01-01)
    The electrochromic switching times of solid state conducting polymer devices fabricated by the ionic self-assembled multilayer method has been investigated. The devices were composed of bilayers of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) and poly(allylamine hydrochloride) on indium tin oxide substrates. Devices fabricated from 40 bilayer thick films have coloration and decolaration switching times of 31 and 6 ms, respectively, with low applied voltage (1.4 V) for an active area of 0.6 cm(2). The switching times have been shown to decrease with the active area of the electrochromic device suggesting that even faster electrochromic switching times are possible for devices with smaller areas. (C) 2008 American Institute of Physics.
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    Synthesis kinetics of CdSe quantum dots in trioctylphosphine oxide and in stearic acid
    Dickerson, B. D.; Irving, D. M.; Herz, E.; Claus, Richard O.; Spillman, William B. Jr.; Meissner, K. E. (AIP Publishing, 2005-04-01)
    A diffusion-barrier model described the early evolution of size-dependent photoluminescence emission from CdSe quantum dots formed by organometallic synthesis. Emission peak widths, emission redshift rates, and nanocrystal growth rates all decreased to a minimum at a reaction completion time. Growth after the completion time by Ostwald ripening was marked by a doubling of the activation energy. The temperature dependence of both reaction completion rates and photoluminescence redshift rates followed Arrhenius behavior governed by activation energies that increased with solvent molecular weight, in this limited case. In stearic acid and in trioctylphosphine oxide, the typical activation energies were 0.6 +/- 0.1 and 0.92 +/- 0.26 eV/molecule, respectively. (c) 2005 American Institute of Physics.