摘要:
Neutron-diffraction experiments were performed on the semiconductor (room-temperature) and insulator (195 K) phases of CD3ND3SnBr3 using a powder diffractometer at KENS. Rietveld refinement revealed fully disordered CD3ND3+ ions (rotating like a spherical shell) in the semiconductor phase (Pm3m, Z = 1, a = 5.899 Angstrom). The insulator phase has a rhombohedral structure with cell doubling in three directions (R3c or R $($) over bar$$ 3c, Z = 8, a = 11.767 Angstrom, alpha = 88.997 degrees), suggesting that the C-N axis of the CD3ND3+ ion is ordered along the crystallographic C-3 or ($) over bar 3 axis and the SnBr6 octahedron is distorted from the regular O-h symmetry.