Vassiliki Katsika-Tsigourakou

A tentative model for estimating the compressibility of multiphased mixed crystals

The growth of multiphased binary and ternary mixed crystals by the melt method using the miscible alkali halides, viz., NaBr and KCl, along with the experimental determination of their compressibility, have been recently reported. These materials are particularly useful for the construction of laser optical windows. Here, we suggest a theoretical model that enables the estimation of the compressibility of the multiphased mixed crystals in terms of the elastic data of the end members alone. The calculated values are in reasonable agreement with the experimental ones. The model makes use of an early suggestion that interconnects the Gibbs energy for the formation and migration of defects in solids, with bulk properties, and has been found of value in a large variety of solids.

Estimating the temperature dependence of the dielectric constant of multiphased mixed crystals

Measurements of the dielectric constant of multiphased binary and ternary mixed alkali halides, which have found a multitude of applications in optical and electronic devices, have been recently reported in the temperature range from room temperature to 423 K. It was found that the temperature variation in the binary mixed crystal (NaCl)0.587 (KBr)0.413 is drastically larger than in any other. We show that this variation can be quantitatively reproduced by means of a simple model, which does not contain any adjustable parameter and solely makes use of the properties of the end members, viz., NaCl and KBr.

A simple model for calculating the compressibility of the transition-metal carbides and nitrides alloys ZrxNb1−xC and ZrxNb1−xN

The 4d-transition-metals carbides (ZrC, NbC) and nitrides (ZrN, NbN) in the rocksalt structure, as well as their ternary alloys, have been recently studied by means of a first-principles full potential linearized augmented plane waves method within the local density approximation. These materials are important because of their interesting mechanical and physical properties, which make them suitable for many technological applications. Here, by using a simple theoretical model, we estimate the bulk moduli of their ternary alloys ZrxNb1−xC and ZrxNb1−xN in terms of the bulk moduli of the end members alone. The results are comparable to those deduced from the first-principles calculations.