Stability of Surface Oxides in an Oxygen Environment

A is the area of the surface unit-cell, and Go surf and Gsurf are the Gibbs free energies of the oxidized and clean surface, respectively, juq and jiiM are the chemical potentials of oxygen and metal atoms, and No is the number of oxygen atoms contained in the oxidized surface structure for which AG jjo) is computed. Finally, AIVm is the difference in the number of metal atoms between the reference clean surface and the oxidized surface structural model. 

When explicitly comparing a set of structures in the sketched atomistic thermod3mamics approach, surfaces with higher O content will become more favorable, the more O-rich the environment. In the limit of low oxygen pressures, the clean surface will obviously be most stable [Apo ——00, cf. (5.4)], but this will eventually change with increasing chemical potential in the gas 

Proceeding to Pd(lll) one observes in most aspects a continuation of the identified trends. As apparent in Fig. 5.10, the again reduced thermal stability of the PdO bulk oxide shows up by a further decreased stability range, which commences nevertheless already at an O chemical potential below the one required to stabilize higher on-surface adsorbate coverages with 0 1/4 ML. 

On the other hand, there is also a qualitatively new feature, since now the experimentally observed, so-called (a/6 x a/6) pseudo-commensurate surface oxide structure displayed in Fig.5.11 is not only a kinetic precursor but 

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