• Vassiliki Katsika-Tsigourakou

      Articles written in Pramana – Journal of Physics

    • A simple model for calculating the bulk modulus of the mixed ionic crystal: NH4Cl1−xBr$_x$

      Vassiliki Katsika-Tsigourakou

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      The ammonium halides are an interesting systems because of their polymorphism and the possible internal rotation of the ammonium ion. The static properties of the mixed ionic crystal NH4Cl$_{1−x}$ Br$_x$ have been recently investigated, using the three-body potential model (TDPM) by applying Vegard’s law. Here, by using a simple theoretical model, we estimate the bulk modulus of the alloys NH4Cl$_{1−x}$ Br$_x$, in terms of the bulk modulus of the end members alone. The calculated values are comparable to those deduced from the three-body potential model (TDPM) by applying Vegard’s law.

    • A tentative model for estimating the compressibility of rock-salt AgCl$_{x}$ Br$_{1−x}$ alloys

      Vassiliki Katsika-Tsigourakou Efthimios S Skordas

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      Ab initio detailed calculations of the elastic properties of AgCl$_{x} Br$_{1−x}$ alloys were recently made using density-functional perturbation theory and by employing the virtual crystal approximation or by means of the full potential linearized augmented plane wave method. Here, we suggest a simple theoretical model that enables estimation of isothermal compressibility of these alloys in terms of the elastic data of end-members alone. The calculated values are in satisfactory agreement with the experimental ones. The present model makes use of an early suggestion that interconnects Gibbs energy for the formation and/or migration of defects in solids with bulk properties.

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