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 B 2 O 3 up to 9 GPa and 1700 K, drawing equilibrium and nonequilibrium phase diagrams of B 2 O 3 . Particularly, we have determined the melting curve, the stability regions for crystalline B 2 O 3 I and B 2 O 3 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 B 2 O 3 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. B 2 O 3 is the first glassformer whose transformations in the disordered state have been comparatively studied for both liquid and glassy phases.