Anionic conductors Ln2/3[Bi12O14](MoO4)5 with Ln = La, Nd, Gd, Ho, Yb. Synthesis–spark plasma sintering–structure–electric properties

A new series of columnar phases Ln2/3□1/3[Bi12O14](MoO4)5 (□ vacancy) with Ln = La, Nd, Gd, Ho and Yb have been synthesized and structurally characterized. They feature the same formula as the molybdate phase Bi2/3□1/3[Bi12O14](MoO4)5 and crystallize in the monoclinic system, space group P2/c. These phases are isostructural with the prototype structure Bi[Bi12O14](MoO4)4(VO4). Pellets of this rare-earth series obtained by spark plasma sintering and measured by impedance spectroscopy show a good anionic conductivity with a parabolic evolution whose maximum is raised by the Gd species at a determined value σ = 6.6 × 10− 3 S cm− 1 at 980 K.