THERMAL VIBRATION ANALYSIS OF RuO2 BY EXAFS

Ruthenium dioxide which has a rutile-type structure is an important material in a viewpoint of electronic and magnetic properties. RuO2 has a negative thermal expansion along c-axis in the high temperature region above room temperature. In this study, we could obtain detailed information about the thermal vibration of atoms by the analysis of EXAFS Debye-Waller factors. EXAFS analysis provides an effective pair potential with temperature dependent shape with Debye-Waller factor. The distance between second-nearest neighbor atoms (Ru-Ru) are equal to the length of c-axis in unit cell. It has become apparent that Ru-O bonds in RuO6 octahedron are much stronger than the interaction between the second-nearest neighbor atoms (Ru-Ru) as same as FeF2 in fluorides. Those results suggest that the negative thermal expansion along c-axis is caused by those weak interactions between second-nearest neighbor atoms (Ru-Ru).