Condensed Matter Physics, 1997, No 9, p. 89-106, English
DOI:10.5488/CMP.9.89
Title: INVESTIGATION OF LOCALLY ANHARMONIC MODELS OF STRUCTURAL
PHASE TRANSITIONS. SEMINUMERICAL APPROACH
Authors: I.V.Stasyuk, K.O.Trachenko (Institute for Condensed Matter
Physics of the
National Academy of Sciences of Ukraine, 1 Svientsitskii St., 290011
Lviv-11, Ukraine)
In the context of description of the structural phase transition in solids,
the anharmonic potential effecting on the ion in the crystal lattice is
selected in the form that in addition to quadric includes cubic
anharmonicity, thus possessing more general non-symmetrical form, and in the
symmetrical form with the Gaussian barrier. The approach based on the
numerical diagonalization of the one-site Hamiltonian matrix is applied. The
peculiarity of the energy spectrum of the system with the Gaussian barrier
potential, particularly the existence of the parts of the spectrum with the
quasidoublets or quasi-equally distanced levels structure which crossover
takes place in the narrow energy interval, is established. The dependencies
of the order parameter, free energy and dielectric susceptibility on the
externally applied field and the order parameter and free energy on the
temperature are derived for various parameters of both models. The phase
diagram (temperature-field) is derived and the influence of the
anharmonicity on the form of the phase coexistence curve and location of the
critical point is studied. It is shown that the asymmetry of the local
potential results in the deviation of the phase coexistence curve from the
vertical line in the plane (temperature-field) and in the appearing of the
first order phase transition occurring as the temperature varies.
Comments: Figs. 16, Refs. 15, Tabs. 2.