JOURNAL OF PHYSICAL CHEMISTRY C, cilt.111, ss.13712-13720, 2007 (SCI İndekslerine Giren Dergi)
Molecular dynamics (MD) simulations, based on a new coordination-dependent charge-transfer potential, were used to study the behavior of crystalline B2O3 in response to various thermal and mechanical constraints. This interaction potential allows for the charges on atoms to redistribute upon the formation and rupture of chemical bonds and dynamically adjusts to multiple coordination states for a given species. Our MD simulations predict that upon isotropic expansion and compression, the B2O3-I crystal transforms into new low- and high-density B2O3 crystals, the stability of which we have further verified using first-principles calculations. The low-density B2O3 crystals (B2O3-0) provide a key to understanding the anomalous thermomechanical behaviors of vitreous B2O3 and the crystallization anomaly of this compound. The high-density B2O3 crystal (B2O3-III), predicted from concurrent MD simulations and first-principles calculations, is different from the known high-pressure phase of B2O3-II crystal, even though the bonding is the same in these two phases. B2O3-III is characterized by a higher energy than B2O3-II at low pressures, but upon further compression the energies of these two phases become indistinguishable. The transformation from B2O3-I to B2O3-III appears to be kinetically favored, especially at low temperatures. Our studies indicate that the phase diagram of B2O3 is much richer than previously known.