Different [Bi12O14]n columnar structural types in the Bi-Mo-Cr-O system:: Synthesis, structure, and electrical properties of the solid solution Bi26MO10-xCrxO69

In order to search for new ionic conductor materials exhibiting a columnar [Bi12O14] structural type, the syntheses of the solid solutions Bi2Mo1-xCrxO6 and Bi26Mo10-xCrxO69 have been undertaken. Single phases were obtained for the last composition with 0 less than or equal to x less than or equal to 5 homogeneity range. Moreover, a new oxide with Bi6Cr2O15 composition has been obtained from the limit nominal stoichiometries Bi2CrO6 and Bi26Cr10O69. X-ray powder diffraction studies have shown that this oxide crystallizes in the orthorhombic system, space group Ccc2 or Cccm, with unit-cell parameters a = 19.8986(9) Angstrom, b = 12.2756(6) Angstrom, c = 5.8868(3) Angstrom, and V = 1437.96 Angstrom(3). Impedance spectroscopy measurements carried out on the representative Bi26Mo8Cr2O69 phase, showed that this material is a good oxygen ion conductor, in fact the best one belongs to the columnar structural type, with a conductivity as high as 1.7 x 10(-3) S cm(-1) at 425 degreesC. (C) 2002 Elsevier Science (USA).