Synthesis, crystal structure, and physical properties of the Gd3BiO3 and Gd8Bi3O8 phases

The second and third known rare-earth bismuthide oxides, Gd3BiO3 and Gd8Bi3O8, have been discovered via high temperature reactions at 1300°C. Like its Gd–Sb–O counterparts, the Gd3BiO3 and Gd8Bi3O8 phases crystallize in the monoclinic C2/m space group, with the latter containing disordered Bi atoms along the b direction of the unit cell. Unlike the RE8Sb3O8 series, the formation of the Gd3BiO3 phase does not necessarily precede the formation of Gd8Bi3O8, which is likely due to the difficulty of accommodating bismuth in the RE–O framework due to its larger size. Physical property measurements performed on a pure Gd8Bi3O8 sample reveal semiconducting behavior. Although electronic structure calculations predict metallic behavior due to an unbalanced electron count, the semiconducting behavior originates from the Anderson localization of the Bi p states near the Fermi level as a result of atomic disorder.