Oxygen diffusion pathway in the anionic conductor Bi26Mo9GeO68

Abstract

A new phase, Bi26Mo9GeO68 was synthesized in the Bi2O3MoO3GeO2 system. The structure determined by single crystal X-ray diffraction crystallizes in the monoclinic system, space group P2/c, with cell parameters at room temperature, a=11.7720(3), b=5.8200(2), c=24.8080(8) Å, β=102.035(2)° and Z=1. The structure investigation gives a R value of 0.043 for 4108 independent hkl reflections. This compound is a typical columnar phase with its [Bi12O14]n columns surrounded by MoO4 tetrahedra and an isolated Bi atom at the junction of (100) and (001) planes containing these tetrahedra. Impedance spectroscopy measurements show that the studied material is a good ionic conductor with a conductivity as high as 3×10−3 Ω−1 cm−1 at 700 °C. In parallel, the X-ray powder diffraction study between room temperature and 700 °C shows the presence of a possible phase transition at about 300 °C. X-ray single crystal studies at various temperatures, 20, 300 and 400 °C, as well as powder neutron diffraction studies up to 500 °C, allowed to show the important vibration of the oxygens of the MoO4 groups designing a probable way for oxygen pathway diffusion. Correlations between structural features and electric properties are developed.