title: Structural evolution and medium range order in permanently densified vitreous SiO2.
abstract: Positron annihilation lifetime spectroscopy is employed to measure the size of the interstitial void spaces characterizing the structure of a set of permanently densified SiO2 glasses. The average volume of the voids is markedly affected by the densification process and linearly shrinks by almost an order of magnitude after a relative density variation of 22%. In addition, x-ray diffraction shows that this change of density does not modify appreciably the short range order, which remains organized in SiO4 tetrahedra. These results strongly suggest a porous medium description for v-SiO2 glasses where the compressibility and the medium range order are dominated by the density variation of the voids volume up to densities close to that of α-quartz.
authors.affiliation: Dipartimento di Fisica, Università di Perugia, I-06123 Perugia, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Zanatta
authors.affiliation: IMEM-CNR, I-43124 Parma, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Baldi
authors.affiliation: Dipartimento di Fisica, Università di Trento, I-38123 Povo, Trento, Italy.
authors.forename: R S
authors.initials: RS
authors.lastname: Brusa
authors.affiliation: Institut für Angewandte Physik und Messtechnik, Universität der Bundeswehr München, D-85577 Neubiberg, Germany.
authors.forename: W
authors.initials: W
authors.lastname: Egger
authors.affiliation: Dipartimento di Fisica, Università di Trento, I-38123 Povo, Trento, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Fontana
authors.affiliation: IMEM-CNR, I-43124 Parma, Italy.
authors.forename: E
authors.initials: E
authors.lastname: Gilioli
authors.affiliation: Dipartimento di Fisica, Università di Trento, I-38123 Povo, Trento, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Mariazzi
authors.affiliation: Dipartimento di Fisica, Università di Trento, I-38123 Povo, Trento, Italy.
authors.forename: G
authors.initials: G
authors.lastname: Monaco
authors.affiliation: Institut für Angewandte Physik und Messtechnik, Universität der Bundeswehr München, D-85577 Neubiberg, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Ravelli
authors.affiliation: Dipartimento di Fisica, Università di Perugia, I-06123 Perugia, Italy and IOM-CNR c/o Dipartimento di Fisica, Università di Perugia, I-06123 Perugia, Italy.
authors.forename: F
authors.initials: F
authors.lastname: Sacchetti