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Abstract:
Rb4O6 displays mixed valency on the anionic lattice and an open p-shell
electronic configuration. At ambient conditions, it exists in a
disordered ground state structure, featuring three different potential
ordering parameters related to phase transitions driven by charge,
orbital and spin ordering. The possible paths of symmetry descent are
analyzed by elaborating the respective group-subgroup relations between
space groups, including the implications that would result from magnetic
ordering. Experimentally, a lower symmetry modification was discovered
and characterized by single-crystal X-ray diffraction [I (4) over bar, Z
= 4, a = 8.688(6), c = 10.362(7) angstrom, R-1 = 0.055, 787 independent
reflections]. The symmetry reduction involved follows one branch of the
B rnighausen tree as predicted, I (4) over bar 3d -> I (4) over bar 2d
-> I (4) over bar convincing evidence was obtained for Rb4O6 undergoing
charge and orbital ordering, along with respective structural order.
