X-ray induced dynamics in borate glasses with different network connectivity

Abstract

Hard x rays induce atomic dynamics in oxide glasses at doses low enough that the average structure is unchanged. X-ray photon correlation spectroscopy is used here to study this effect in a series of alkali borate glasses characterized by different network connectivity. The product of the x-ray dose rate per atom and the decay time of the density correlation function is a sample-dependent parameter with the dimensions of an energy: It varies between a fraction of eV and few tens of eV and is sensitive to the network connectivity of the glass. It can then be used to access some bonding information also in cases where the x rays perturb the material, a regime of great interest in modern x-ray-based experiments.

X-ray driven and intrinsic dynamics in protein gels

“…Such flux dependent dynamics have been observed before in XPCS experiments on oxide and network glasses 26 – 29 , albeit with orders of magnitude higher dose rates, and also recently in dense protein glasses 30 . In our case the dynamics of the protein gels are governed by stress relaxations in which the correlation functions can be modeled as a series of consecutive relaxation events in the stressed material 68 , 74 .…”

Stochastic atomic acceleration during the X-ray-induced fluidization of a silica glass

“…One key point, however, is that the data discussed here show a complex dose and dose rate dependence that has to be disentangled. The dose rate dependence has been discussed in previous studies, where it was shown that the decay time of the intensity correlation functions scales with the inverse of the dose rate ( 1 – 5 ). For what concerns the dose dependence, in the Inset of Fig.…”

“…The claim of local fluidization comes from the observation that the density correlation function at the interatomic length scale decays to zero under X-ray irradiation: This is a sign of a complete renewal of the atomic configuration typical of a liquid but not of a glass. The characteristic timescale, τ ( q ), of such configuration renewal turns out to be inversely proportional to the X-ray dose rate ( 1 – 5 ).…”

“…Recent experiments carried out using wide-angle X-ray photon correlation spectroscopy (XPCS) have revealed that X-rays in the 10-keV range induce in some oxide glasses local fluidization of the material via a nonthermal process ( 1 – 5 ). XPCS probes the q component of the density correlation function, F ( q , t )=⟨ ρ q * (0) ρ q ( t )⟩, where q is the scattering vector and ρ q ( t ) is the q component of the microscopic density Lehmkuhler et al ( 6 ).…”

“…To compare the present results with those in the literature ( 1 ), it is then necessary to evaluate the data at the same dose, D , and then scale them to the same dose rate, d r ( 2 , 5 ). In particular, the computation of correlation functions intrinsically relies on information at different ages (and thus doses).…”