Sommaire:

Despite its chemical simplicity, boron trioxyde appears a puzzling system, as it does not crystalles under normal conditions of temperature and pressure. It was hypothesized, based on DFT calculation in the GGA approximation, that this 'crystallization anomaly' resulted from the existence of a 'hidden' low energy polymorphism (see Ref. 1).
In a previous work, we showed that including dispersion effects was critical for an accurate description of the volume and energetics of SiO2 polymorphs (see Ref. 2). SiO2 and B2O3 being the two textbook examples of network forming oxydes, it is to be expected that dispersion effects also play a crucial role in the ab initio description of B2O3's hidden polymorphism. We consequently use van der Waals corrected density functional theory and Quantum Monte Carlo to investigate B2O3 polymorphs. We show that some conclusions of Ref. 1 must be modified, and we use this methodology to predict the properties of the newly found polymorphs. It is demonstrated that most structures have interesting mechanical properties, including high porosity, strong anisotropy, and negative linear compressibility.

Ref. 1 : 'Hidden polymorphs drive vitrification in B2O3', Guillaume Ferlat, Ari Paavo Seitsonen, Michele Lazzeri & Francesco Mauri,Nature Materials 11, 925-929 (2012).

Ref. 2: 'Dispersion effects in SiO2 polymorphs: An ab initio study', Henri Hay, Guillaume Ferlat, Michele Casula, Ari Paavo Seitsonen, and Francesco Mauri, Phys. Rev. B 92, 144111 (2015)

Pour plus d'informations, merci de contacter Ispas S.