“…The β-pyrochlore oxides AOs 2 O 6 have recently been attracting much attention, [1][2][3][4] as they exhibit an unusual atomic vibration in a solid called rattling, 5,6) which is essentially a local, anharmonic vibration of a heavy ion confined in an oversized atomic cage. They crystallize in a cubic crystal structure of space group Fd-3m with all the atoms sitting at special positions, i.e., the A, Os and O atoms at the 8b, 16c and 48f sites, respectively.…”