Journal
PHYSICAL CHEMISTRY CHEMICAL PHYSICS
Volume 17, Issue 26, Pages 17301-17310Publisher
ROYAL SOC CHEMISTRY
DOI: 10.1039/c5cp02252e
Keywords
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Funding
- National Science Foundation [EAR-1114313, DMR-1231586]
- DARPA [W31P4Q1310005, W31P4Q1210008]
- Basic Research Foundation of NWPU [JCY20130114]
- National Natural Science Foundation of China [51372203, 51332004]
- Foreign Talents Introduction
- Academic Exchange Program of China [B08040]
- Government of Russian Federation [14.A12.31.0003]
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With the motivation of exploring new high-strength ceramics, ab initio evolutionary simulations are performed to search for all the stable compounds in the Zr-O system. We have found that not only the traditional compound ZrO2, but also the ordered suboxides R (3) over bar -Zr6O, R (3) over barc-Zr3O, P (3) over bar 1m-Zr2O and P (6) over bar 2m-ZrO are stable at zero pressure. The crystal structure of semimetallic P (6) over bar 2m-ZrO consists of Zr-graphene layers and can be described as an intercalated version of the omega-Zr structure. An interesting massive Dirac cone is found in the three-dimensional (3D) band structure of P (6) over bar 2m-ZrO at the Gamma-point. The elastic properties, the hardness and the correlation between the mechanical properties of Zr-O compounds and the oxygen content have been systematically investigated. Surprisingly, the hardest zirconium oxide is not ZrO2, but ZrO. Both P (6) over bar 2m-ZrO and P (3) over bar 1m-Zr2O exhibit relatively high hardness values of 14 GPa and 10 GPa, respectively. The anisotropic Young's modulus E, torsion shear modulus G(t) and linear compressibility beta have been derived for P (6) over bar 2m-ZrO and P (3) over bar 1m-Zr2O. Further analyses of the density of states, the band structure and the crystal orbital Hamilton population indicate that the electronic structure of Zr-O compounds is directly related to their mechanical properties. The simultaneous occurrence of the 3D-framework of Zr-O and the strong Zr-Zr bonds in P (6) over bar 2m-ZrO explains its high hardness.
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