We derive a formula, useful for first-principles calculations, which relates the free energy of an oxide/metal interface to the free energies of surfaces and the work of separation of the interface. We distinguish the latter mechanical quantity from the thermodynamic work of adhesion, and we describe explicitly how both may be calculated. Our formulae for interfacial and surface energies are cast in terms of quantities which can be calculated or looked up in tables, and include as additional parameters the ambient temperature and partial pressure of oxygen PO 2 . From total energy calculations for the Nb(111)/α−Al2O3 (0001) interface, free Nb and Al2O3 surfaces, we obtain firstly numerical estimates of the works of separation, which are independent of PO 2 . We then obtain surface energies, interfacial energies and the equilibrium work of adhesion as a function of PO 2 .

No abstract

Given that H(2)O dissolves minimally in quartz, the mechanism for the ubiquitous dissolution of H(2)O in silica glasses has been a long-standing puzzle. We report first-principles calculations in prototype silica glass networks and identify the ring topologies that allow the exothermic dissolution of H(2)O as geminate Si-O-H groups. The topological constraints of these reactions explain both the observed saturation of Si-O-H concentrations and the observed increase in the average Si-Si distance. In addition, calculations of H(2)O and Si-O-H dissociation account for the observed response to radiation by wet thermally grown SiO(2).

With the exception of Li, alkali metals do not react with elemental nitrogen neither at ambient conditions nor at elevated temperatures, requiring the search for alternative synthetic routes to their nitrogen-containing compounds. Here using a controlled decomposition of sodium azide NaN3 at high pressure conditions we synthesize two novel compounds Na3(N2)4 and NaN2 both containing dinitrogen anions. NaN2 synthesized at 4 GPa might be the common intermediate in high-pressure solid-state metathesis reactions where NaN3 is used as a source of nitrogen, while Na3(N2)4 opens a new class of compounds, where [N2] units accommodate a non-integer formal charge of -0.75. This finding can dramatically extend the expected compositions in other group 1-2 metal-nitrogen systems. Electronic structure calculations show the metallic character for both compounds.