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Iowa State University

Series

Materials Science and Engineering

1992

Articles 1 - 3 of 3

Full-Text Articles in Physics

Twinned One-Dimensional Quasicrystals In Bridgman-Grown Al-Si-Cu-Co Alloys, L. X. He, Thomas A. Lograsso, Alan I. Goldman Jul 1992

Twinned One-Dimensional Quasicrystals In Bridgman-Grown Al-Si-Cu-Co Alloys, L. X. He, Thomas A. Lograsso, Alan I. Goldman

Ames Laboratory Publications

Single grains of Al60Si2Cu18Co20 with a decaprismatic morphology were grown by the Bridgman method and studied by transmission electron microscopy and x-ray diffraction. Although the diffraction patterns of these grains superficially resemble that of a decagonal quasicrystal, a closer inspection reveals that they are composed of tenfold twins of a one-dimensional quasicrystal along with small domains of three crystalline approximant phases.


Relaxation And Fluctuations In Glassy Fast-Ion Conductors: Wide-Frequency-Range Nmr And Conductivity Measurements, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin, Hitendra K. Patel Jul 1992

Relaxation And Fluctuations In Glassy Fast-Ion Conductors: Wide-Frequency-Range Nmr And Conductivity Measurements, Ferdinando Borsa, D. R. Torgeson, Steve W. Martin, Hitendra K. Patel

Materials Science and Engineering Publications

Li7 nuclear spin-lattice relaxation rates (R1) versus the temperature at several resonance frequencies (4 to 40 MHz) are reported together with the conductivity measurements, σ(ω), in the range 1 Hz to 3.76 MHz on 0.56Li2S+0.44Si2S, a glassy fast-ionic conductor. Both R1 and σ(ω) are fitted consistently over the whole temperature and frequency range by using a stretched-exponential, i.e., exp(-t/τ*c)β for the corresponding correlation functions (CF). Formulas that relate R1(ω) and σ(ω) and that give the asymptotic behavior as functions of T and ω of both quantities are ...


Fast Ionic Conduction In Na2s+B2s3 Glasses: Compositional Contributions To Nonexponentiality In Conductivity Relaxation In The Extreme Low-Alkali-Metal Limit, Hitendra K. Patel, Steve W. Martin May 1992

Fast Ionic Conduction In Na2s+B2s3 Glasses: Compositional Contributions To Nonexponentiality In Conductivity Relaxation In The Extreme Low-Alkali-Metal Limit, Hitendra K. Patel, Steve W. Martin

Materials Science and Engineering Publications

The conductivity relaxation phenomenon in glassy and crystalline ionic conductors has been known for many years to be a highly nonexponential process. The stretched exponential function exp-(t/τ)β has been used with varying levels of success to describe this relaxation. Whether the nonexponentiality is due to parallel conducting processes acting independently of each other and having a distribution of relaxation times or to serial processes strongly coupling the ionically conducting species and constraining each other’s relaxation, the exact nature of this process is still unknown. If coupling is the active mechanism responsible for the nonexponentiality, then there ...