• S Dattagupta

      Articles written in Bulletin of Materials Science

    • Nonequilibrium phase transitions

      S Dattagupta

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      A brief review is provided of the subject of nonequilibrium phase transitions occurring in various systems in different disciplines. All these systems exhibit a similar kind of ordering phenomena at a macroscopic level and can therefore be classified in terms of appropriate order parameters. Typical order parameter equations are discussed in the light of Landau’s phenomenological theory of phase transitions. The instabilities occurring in a few chemical reactions are discussed in some detail and the role of fluctuations pointed out. Mention is also made of the possibility of viewing some metallurgical phenomena as examples of nonequilibrium phase transitions.

    • The tricritical point — a qualitative overview

      S Dattagupta

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      The concept of tricritical points is introduced by way of examples of ordinary liquid mixtures and mixtures of normal He3 and superfluid He4. A prototype Ising spin model is used for a qualitative discussion of the mechanisms behind the occurrence of tricritical phenomena. Mention is also made of the other theoretical developments.

    • Quantum diffusion of hydrogen

      S Dattagupta

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      A brief overview is given on low temperature diffusive behaviour of H in Nb(OH)x, and measurement of diffusion, primarily by neutron scattering. We go in some detail into recent work on calculations of neutron structure factor as well as the diffusion coefficient of hydrogen, influenced by two-level excitations. Both the electronic and phononic contributions are covered. The importance of similar two-level excitations in insulating and metallic glasses is also pointed out.

    • Kinetics of oxygen defect in YBCO

      S Dattagupta S K Ghoshal

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      Monte-Carlo simulations are described using the Kawasaki model of oxygen (dis)ordering in the basal plane of YBa2Cu3O7−δ(YBCO). In this model the presence or absence of an interstitial oxygen defect is mapped into a pseudo Ising spins=+1 or − 1. We study the rate law and the relaxation time of the order parameter and most importantly, the diffusion of oxygen in the basal plane across the structural phase transition in this system. In a separate investigation we have carried out numerical analysis of a mean-field dynamical model (with Kawasaki kinetics) to examine phase ordering dynamics and pattern formation, for δ=0.

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