The crystal structure of β-Na2Cr2O7

Sodium rubidium dichromate and sodium caesium dichromate

“…This structure determination was undertaken as part of a study of the structure and polymorphism of alkali metal dichromates. The dichromate ions are similar to those found in Na2Cr207 (Panagiotopoulos & Brown, 1972) and Rb2Cr207 (Panagiotopoulos & Brown, 1970;L~fgren, 1971 ;L~Sfgren & Waltersson, 1971) with Cr-O-Cr angles of 135.9 (6) and 141.4 (6) ° .…”

The crystal structure of α-Na2Cr2O7 and the α–β phase transition

“…The structure is closely related to that offl-Na2Cr207 which has been described in detail by Panagiotopoulos & Brown (1972a). The two crystallographically distinct (010) layers of fl-Na2Cr207 become identical in c~-Na2Cr207 and the conformation of the high temperature layer is almost midway between those of the two low temperature layers giving a structure that is intermediate between the thortveitite-type and the dichromate-type of structure (Brown & Calvo, 1970).…”

“…The atomic coordinates obtained during the refinement of the structure of the fl phase in the superstructure space group A1 (Panagiotopoulos & Brown, 1972a) were used as the initial coordinates for the phase structure. This model was refined with isotropic temperature factors, individual scale factors for each layer and unit weights.…”

“…The single crystal of fl-Na2Cr207 used for this work was prepared by the method described by Panagiotopoulos & Brown (1972a) and was sealed in a thinwalled quartz capillary tube in a nitrogen atmosphere.…”

“…In a previous paper (Panagiotopoulos & Brown, 1972a) we reported the crystal structure of the room temperature (fl) phase of Na2Cr207. Above 240°C the crystal undergoes a displacive phase transition to ~-Na2Cr207 in a way which does not destroy the crystal.…”