Benzophenone glass, supercooled liquid, and crystals: elastic properties and phase transitions

Abstract

The elastic properties of glass α- and β-modifications of benzophenone (C₆H₅)₂CO are determined for the first time by the ultrasonic method at high pressures up to 1 GPa and in the temperature range of 77 K< T < 293 K. Four states of benzophenone are experimentally observed in the investigated temperature range of 77–293 K: glass, supercooled liquid, and α- and β-crystalline phases. The boundaries of phase transitions during isobaric heating are determined. The bulk and shear moduli B and G, Poisson's ratio σ, and density ρ are calculated. Glassy benzophenone has much lower elastic moduli than the α-modification at 77 K (the shear modulus G of glass is about half the value for the crystal). The crystalline α-modification demonstrates a strong softening of both moduli with an increase in the temperature in the range of 77–293 K. Heating of glass leads to the formation of a very viscous supercooled liquid, which crystallizes into the metastable β-modification. A further increase in the temperature leads to a monotropic phase transition β → α.