MEAN-SQUARE DISPLACEMENTS OF ATOMS IN HEXABORIDES

High-resolution neutron powder and single-crystal X-ray diffraction st udies has been used to investigate the temperature dependencies of ato mic mean-square displacements in rare-earth hexaborides. The experimen tal data on elastic constants and phonon frequencies have been used to improve the valence force field parameters for SmB6 and the temperatu re dependencies of atomic mean-square displacements in SmB6 is compare d with theoretical values. The correlation between ionic radii and mea n-square displacements of rare-earth atoms are shown.