Crystal structure of La2Mo2O9 single crystals doped with bismuth

Precision X-ray diffraction studies of La_{2 − x} Bi _x Mo₂O₉ (x = 0.04, 0.06, and 0.18) single crystals are performed. It is found that in the compounds doped with bismuth, analogously with the structure of the metastable β_ms phase of pure La₂Mo₂O₉ (LM), the La, Mo1, and O1 atoms deviate from the threefold axis on which they are located in the high-temperature β phase. It is shown that bismuth atoms substitute for part of lanthanum atoms and occupy a position at the threefold axis in the neighborhood of the split lanthanum position. The implantation of bismuth atoms in the LM structure results in the return of a part of the molybdenum atoms to the position at the threefold axis. The occupancy of this position is equal to the occupancy of the bismuth atomic position.