Structural transformations in liquid, crystalline, and glassy B2O3 under high pressure

We present in situ (x-ray diffraction) and ex situ (quenching) structural studies of crystalline, liquid, and glassy B2O3 up to 9 GPa and 1700 K, drawing equilibrium and nonequilibrium phase diagrams of B2O3. Particularly, we have determined the melting curve, the stability regions for crystalline B2O3 I and B2O3 II modifications, the regions of transformations, such as densification or crystallization, for both the liquid and glassy states, including the region of sharp first-order-like transition in liquid B2O3 to a high-density phase near 7 GPa. Quenching experiments also show that the transition to the high-density liquid can occur at much lower pressures in nonstoichiometric melts with an excess of boron. B2O3 is the first glassformer whose transformations in the disordered state have been comparatively studied for both liquid and glassy phases. (C) 2003 MAIK "Nauka/Interperiodica".