title: Fracture-induced amorphization of polycrystalline SiO2 stishovite: a potential platform for toughening in ceramics.
abstract: Silicon dioxide has eight stable crystalline phases at conditions of the Earth's rocky parts. Many metastable phases including amorphous phases have been known, which indicates the presence of large kinetic barriers. As a consequence, some crystalline silica phases transform to amorphous phases by bypassing the liquid via two different pathways. Here we show a new pathway, a fracture-induced amorphization of stishovite that is a high-pressure polymorph. The amorphization accompanies a huge volume expansion of ~100% and occurs in a thin layer whose thickness from the fracture surface is several tens of nanometers. Amorphous silica materials that look like strings or worms were observed on the fracture surfaces. The amount of amorphous silica near the fracture surfaces is positively correlated with indentation fracture toughness. This result indicates that the fracture-induced amorphization causes toughening of stishovite polycrystals. The fracture-induced solid-state amorphization may provide a potential platform for toughening in ceramics.
authors.affiliation: 1] Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany [2] Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency (JST), Chiyoda-ku, Tokyo 102-0075, Japan.
authors.forename: Norimasa
authors.initials: N
authors.lastname: Nishiyama
authors.affiliation: Secure Materials Center, Materials and Structures Laboratory, Tokyo Institute of Technology, R3-23 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Wakai
authors.affiliation: Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ohfuji
authors.affiliation: Japan Synchrotron Radiation Research Institute/SPring-8, 1-1-1 Kouto, Sayo, Hyogo 679-5198, Japan.
authors.forename: Yusuke
authors.initials: Y
authors.lastname: Tamenori
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Hidenobu
authors.initials: H
authors.lastname: Murata
authors.affiliation: National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: Department of Mechanical Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Matsushita
authors.affiliation: Department of Mechanical Engineering, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan.
authors.forename: Manabu
authors.initials: M
authors.lastname: Takahashi
authors.affiliation: 1] Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany [2] National Research Nuclear University (MEPhI), Kashirskoe shosse 31, Moscow, 115409, Russia.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Kulik
authors.affiliation: Secure Materials Center, Materials and Structures Laboratory, Tokyo Institute of Technology, R3-23 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japan.
authors.forename: Kimiko
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: Fuji Die Co., Ltd., 2-17-10 Shimomaruko, Ohta-ku, Tokyo 146-0092, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Wada
authors.affiliation: Deutsches Elektronen-Synchrotron (DESY), Notkestr. 85, 22607 Hamburg, Germany.
authors.forename: Jozef
authors.initials: J
authors.lastname: Bednarcik
authors.affiliation: 1] Geodynamics Research Center, Ehime University, 2-5 Bunkyo-cho, Matsuyama 790-8577, Japan [2] Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1-1E-1 Ookayama, Meguroku, Tokyo 152-8500, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Irifune