Local dynamics and local thermal expansion around light elements in the bulk and on surfaces

Abstract

Temperature-dependent EXAFS measurements at the oxygen and fluorine K-edges of bulk single crystal oxides and fluorides and low- Z-surface systems are studied. Mean-square and mean-cubic relative variations of the nearest-neighbor bond length of the oxygen and fluorine atoms are determined using the cumulant expansion. Simple quantum mechanical models for the description of the atomic motion yield EXAFS Debye- and Einstein-temperatures as well as the local thermal expansion. Good agreement of the thermal expansion locally measured by EXAFS and macroscopically measured by other techniques is established for FCC-metals and for bulk CaF 2. In oxygen surface systems the local thermal expansion is enlarged in comparison to corresponding bulk materials.