A new concept has been developed expressing the hardness of covalent and ionic crystals by means of charge density and local structure of matter, and, therefore, hardness is determined by first-principles calculations. For the first time, the expression for hardness related to crystal orientation is proposed, because calculations use strength of bonds and take into account the directions of inter-atomic bonds. It is shown that a lower coordination number of atoms results in higher hardness and that hardness predominantly reflects the strength of bonds transversely oriented to the direction of indentation. Both surprising results are in variance with general opinion presented in current literature.
Autoři: Antonín Šimůnek, Jiří Vackář
Odkazy:
A. Šimůnek and J.Vackář, 2006: Hardness of Covalent and Ionic Crystals: First-Principle Calculations. Phys. Rev. Letters, Vol. 96, p. 085501 (2006).
A. Šimůnek, 2007: How to estimate hardness of crystals on a pocket calculator. Phys. Rev. B, Vol. 75, p. 172708.
A. Šimůnek, 2009: Anisotropy of hardness from first principles: The cases of ReB2 and OsB2. Phys. Rev. B, Vol. 80, p. 060103(R).
Proč je tvrdost krystalů závislá na jejich orientaci?
What makes it so hard?
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