skip to main content

Title: Phonons, nature of bonding, and their relation to anomalous thermal expansion behavior of M{sub 2}O (M = Au, Ag, Cu)

We report a comparative study of the dynamics of Cu{sub 2}O, Ag{sub 2}O, and Au{sub 2}O (i.e., M{sub 2}O with M = Au, Ag, and Cu) using first principle calculations based on the density functional theory. Here, for the first time, we show that the nature of chemical bonding and open space in the unit cell are directly related to the magnitude of thermal expansion coefficient. A good match between the calculated phonon density of states and that derived from inelastic neutron scattering measurements is obtained for Cu{sub 2}O and Ag{sub 2}O. The calculated thermal expansions of Ag{sub 2}O and Cu{sub 2}O are negative, in agreement with available experimental data, while it is found to be positive for Au{sub 2}O. We identify the low energy phonon modes responsible for this anomalous thermal expansion. We further calculate the charge density in the three compounds and find that the magnitude of the ionic character of the Ag{sub 2}O, Cu{sub 2}O, and Au{sub 2}O crystals is in decreasing order, with an Au-O bond of covalent nature strongly rigidifying the Au{sub 4}O tetrahedral units. The nature of the chemical bonding is also found to be an important ingredient to understand the large shift of the phononmore » frequencies of these solids with pressure and temperature. In particular, the quartic component of the anharmonic term in the crystal potential is able to account for the temperature dependence of the phonon modes.« less
Authors:
; ;  [1] ;  [2]
  1. Solid State Physics Division, Bhabha Atomic Research Centre, Trombay, Mumbai 400085 (India)
  2. Institut Laue-Langevin, BP 156, 38042 Grenoble Cedex 9 (France)
Publication Date:
OSTI Identifier:
22277932
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 115; Journal Issue: 9; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; CHARGE DENSITY; CHEMICAL BONDS; COPPER OXIDES; COVALENCE; CRYSTALS; DENSITY FUNCTIONAL METHOD; GOLD OXIDES; INELASTIC SCATTERING; NEUTRON DIFFRACTION; PHONONS; POTENTIALS; PRESSURE DEPENDENCE; SILVER OXIDES; TEMPERATURE DEPENDENCE; THERMAL EXPANSION