title: Transparent polycrystalline cubic silicon nitride.
abstract: Glasses and single crystals have traditionally been used as optical windows. Recently, there has been a high demand for harder and tougher optical windows that are able to endure severe conditions. Transparent polycrystalline ceramics can fulfill this demand because of their superior mechanical properties. It is known that polycrystalline ceramics with a spinel structure in compositions of MgAl2O4and aluminum oxynitride (γ-AlON) show high optical transparency. Here we report the synthesis of the hardest transparent spinel ceramic, i.e. polycrystalline cubic silicon nitride (c-Si3N4). This material shows an intrinsic optical transparency over a wide range of wavelengths below its band-gap energy (258 nm) and is categorized as one of the third hardest materials next to diamond and cubic boron nitride (cBN). Since the high temperature metastability of c-Si3N4in air is superior to those of diamond and cBN, the transparent c-Si3N4ceramic can potentially be used as a window under extremely severe conditions.
authors.affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany.
authors.forename: Norimasa
authors.initials: N
authors.lastname: Nishiyama
authors.affiliation: Institute of Engineering Innovation, The University of Tokyo, 2-11-16 Yayoi, Bukyo-ku, Tokyo, 113-8656, Japan.
authors.forename: Ryo
authors.initials: R
authors.lastname: Ishikawa
authors.affiliation: Geodynamics Research Center, Ehime University, 2-5 Bukyo-cho, Matsuyama, 790-8577, Japan.
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Ohfuji
authors.affiliation: Bayerisches Geoinstitut, Universität Bayreuth, 95440, Bayreuth, Germany.
authors.forename: Hauke
authors.initials: H
authors.lastname: Marquardt
authors.affiliation: Bayerisches Geoinstitut, Universität Bayreuth, 95440, Bayreuth, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Kurnosov
authors.affiliation: National Institute for Materials Sciences, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.affiliation: National Institute for Materials Sciences, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Byung-Nam
authors.initials: BN
authors.lastname: Kim
authors.affiliation: National Institute for Materials Sciences, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan.
authors.forename: Hidehiro
authors.initials: H
authors.lastname: Yoshida
authors.affiliation: Graduate School of Science and Technology, Hirosaki University, 3 Bunkyo-cho, Hirosaki, 036-8561, Japan.
authors.forename: Atsunobu
authors.initials: A
authors.lastname: Masuno
authors.affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany.
authors.forename: Jozef
authors.initials: J
authors.lastname: Bednarcik
authors.affiliation: Deutsches Elektronen-Synchrotron DESY, Notkestr. 85, 22607, Hamburg, Germany.|Bayerisches Geoinstitut, Universität Bayreuth, 95440, Bayreuth, Germany.
authors.forename: Eleonora
authors.initials: E
authors.lastname: Kulik
authors.affiliation: Institute of Engineering Innovation, The University of Tokyo, 2-11-16 Yayoi, Bukyo-ku, Tokyo, 113-8656, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Ikuhara
authors.affiliation: Laboratory for Materials and Structures, Tokyo Institute of Technology, R3-23, 4259 Nagatsuta-cho, Midori-ku, Yokohama, 226-8503, Japan.
authors.forename: Fumihiro
authors.initials: F
authors.lastname: Wakai
authors.affiliation: Geodynamics Research Center, Ehime University, 2-5 Bukyo-cho, Matsuyama, 790-8577, Japan.|Earth-Life Science Institute, Tokyo Institute of Technology, 2-12-1-1E-1 Ookayama, Meguro-ku, Tokyo 152-8500, Japan.
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Irifune