504 publications from this institution
Ab initio MD studies of the structural and electronic properties of K–Te alloys at three different stoichiometric compositions are presented. The tellurium-rich mixture K0.12Te0.88 is entirely determined by the Te atoms, with a structure and electronic properties that are very similar to those of pure liquid Te. The properties of equiatomic KTe at 770 K are determined by the strong iono-covalent bonding, but the order of the crystalline phase, consisting of Te2 2− dumbbells in a matrix of K cations, is blurred to a very high degree. The strong coupling of the potassium cations to the Te system is also shown by the diffusion constant. In the octet compound K2Te at 1300 K we found that the ionic character of the solid salt is preserved in the liquid. The electronic properties of both liquid mixtures, although modified by thermal disorder, show some similarities to the crystalline phases, especially a deep minimum at the Fermi edge, confirming the low conductivity values that are experimentally measured.
In recent years, the formation of thin, well-ordered but complex surface oxides on late transition metals has been discovered. The driving force for this line of research has been the strong incentive to increase the partial pressure of oxygen from ultra-high vacuum to conditions more relevant for heterogeneous catalysis. Here we review the present status of the research field. Compared to oxygen adatom superstructures, the structure of the surface oxides has proven to be extremely complex, and the investigations have therefore relied on a combination of several experimental and theoretical techniques. The approach to solving the structures formed on close-packed surfaces of Pd and Rh is presented in some detail. Focusing on the structures found, we show that the surface oxides share some general properties with the corresponding bulk oxides. Nevertheless, of all surface oxide structures known today, only the two-dimensional surface oxides on Pd(100) and Pt(110) have the same lattice as the bulk oxides (PdO and PtO, respectively). In addition to two-dimensional oxides, including the O–Rh–O trilayers found on Rh, one-dimensional oxides were observed at ridges or steps of open surfaces such as (110) or vicinal surfaces. Finally, we briefly report on a few studies of the reactivity of surface oxides with well-known structure.
