Amorphous-amorphous transformation induced in glasses by intense x-ray beams

The atomic displacements induced by an x-ray beam of relatively low energy, epsilon similar to 8 KeV, are investigated in pure boron oxide and in a set of sodium silicate glasses by means of x-ray photon correlation spectroscopy. We observe the complete x-ray induced transformation of the initial glass into a new amorphous state which remains stable under irradiation. The new phase continues to rearrange under the beam with a stretched exponential relaxation similar to the one observed with macroscopic measurements in the corresponding high-temperature supercooled liquid, suggesting that the new configuration lies in a higher energy minimum of the potential energy landscape. We investigate the temperature dependence of the observed dynamics for a specific sodium concentration and we observe a temperature dependence of the beam induced motion, which suggests that the defect creation rate is thermally activated. The radiation dose needed for the initial structural variation is sample dependent and correlates well with the number of constraints per vertex, within the framework of rigidity theory. This observation provides a quantitative tool to evaluate the efficiency of the radiolytic process in different network topologies.