The substitutional disorder of tetrahedral atoms in the feldspar albit
e has been studied by a Monte Carlo method, which takes into account a
tom displacements along with interchanges between Al and Si atoms. The
atom ordering is characterized by a long-range order parameter, which
suffers a sharp decrease around 1000 K, followed by a slower decrease
up to 1250 K, the temperature at which the long-range order is lost.
These results are in agreement with earlier X-ray diffraction data. Th
e interdependence between atom ordering and lattice relaxation has bee
n analyzed by means uf radial distribution functions for framework ato
ms and Na cations, as well as by mean-square displacements of the atom
s as a function of temperature. Our results indicate a strong coupling
between Al, Si atom distribution and lattice relaxation. The Monte Ca
rlo method is shown to be very helpful to analyze this order-disorder
problem at a microscopic level.