Аннотация:Computer modelling of NaCl-KCl (halite - sylvite) solid solution
was accomplished by atomistic pair potentials with using of
GULP program [1], which is based on search of energy minimum.
The mixing properties of NaCl-KCl solid solution (enthalpy ΔH,
interaction parameter Q, deviations from additivity of unit cell
volume ΔV and bulk modulus ΔK) are in quite good agreement
with the recent experimental data [2] and essentially confirm the
main conceptions of crystal chemical theory of solid solutions [3].
Calculated vibrational entropy ΔS which is nearly independent on
temperature plays important role in the mixing Gibbs energy. The
latter allows us to obtain stability boundaries of solid solution, which
are in good agreement with experimental decomposition diagram.
Analysis of solid solution structure relaxation leads to conclusion
that both anionic and cationic sublattices are distorted, but anionic
one is distorted much more. Calculations of local valence balance on
all types of ionic sites reveal the deviations from valence balance on
cationic sites, whereas the general balance is maintained. The values
of electrostatic potential in ionic positions display the reduction of
bonding force in solid solution in comparison with pure crystals NaCl
and KCl.
[1] Gale J.D., Rohl A.L. // Mol. Simul., 2003. V. 29. No. 5. P.
291-341.
[2] Walker D., Verma P.K., Cranswick L.M.D., Jones R.L., Clark
S.M., Buhre S. // Amer. Miner. 2004. V. 89. P. 204-210; 2005. V. 90.
P. 229-239.
[3] Urusov, V. (2001): The phenomenological theory of solid
solutions. In Geiger, C.A. (ed.): Solid solutions in silicate and oxide
systems /EMU Notes Mineral., 3/. Budapest: Eötvös Univ. Press,
121-153.
Keywords: solid solutions, mineral crystal structures,
computer modelling solids