A new series of columnar phases Ln(2/3)square(1/3)[Bi12O14](MoO4)(5) (square vacancy) with Ln=La, Nd, Gd, Ho and Yb have been synthesized and structurally characterized. They feature the same formula as the molybdate phase Bi-2/3 square(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 sigma=6.6 x 10(-3) S cm(-1) at 980 K. (c) 2006 Elsevier B.V. All rights reserved.