Thermal Vibrations in Ba sub 2 YCu sub 3 O sub 7 Studied by X-ray Diffraction.

The thermal motion of the atoms in Ba sub 2 YCu sub 3 O sub 7 was recently using X-ray diffraction. The refined Debye- Waller factors of the individual atoms are consistent with the local environment. Anharmonic expansion terms of the thermal parameters were obtained for the metal atoms. Notably, the copper and the barium atoms show strong anharmonic features that result in the redistribution of the electron density around these atoms. Possible implications of the observed features will be discussed.