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Journal of Physical Studies 24(3), Article 3601 [6 pages] (2020)
DOI: https://doi.org/10.30970/jps.24.3601 SHORT RANGE ORDER AND CONFIGURATIONAL ENTROPY OF INTERMEDIATE PHASES IN THE LIQUID STATE
Z. M. Oliinyk1, A. V. Korolyshyn1
1Faculty of Physics, Ivan Franko National University of Lviv,
8 Kyrylo and Mefodiy St., Lviv, UA–79005, Ukraine
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The configurational entropy of mixing was calculated on the basis of the experimental diffraction data of melts of intermediate phases of Cu-In, Bi-Te, Fe-Ge, Ni-In and Bi-Tl systems. The entropy determined in such a way is the difference between the entropy of the melt and the one of an ideal gas of the same atoms being a measure of the degree of ordering of the melt. This value is in fact the excess entropy and differs from the classical definition of configurational entropy for crystals, defined as the difference between total entropy and its vibrational contribution. This approach was used to calculate such a configurational contribution to entropy in the case of one-component melts, but we tried to use it to study two-component melts too, replacing them by effective one-component liquids.
Configuration entropy indicates the deviation of the topology of the real atomic distribution from the distribution in the gas of the same atoms, and in the case of binary melts, we have calculated the degree of deviation of the structural state of the melt from the structure of an ideal atomic solution. For a melt with an average atomic distribution, the excess configuration entropy is close to zero, and in the case of significant changes in the atomic distribution during the formation of the melt, it will be different. The transformation of the structure during the melt formation is accompanied by both a change in the interparticle interaction and the topology of the atomic distribution in comparison with the pure components, and these changes will be displayed in the experimental pair correlation function and hence in the configurational entropy of mixing.
The concentration dependence of the excess configurational entropy within the concentration range corresponding to the existence of intermediate phases of the studied systems is characterized by minimal values and increases within concentration intervals in which eutectics and atomic solutions exist, that is the evidence of its correlation with equilibrium diagrams of the studied systems.
Key words: metal melts, configuration entropy, short range order.
