| Autor: |
Fop S; Department of Chemistry, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, United Kingdom., Wildman EJ; Department of Chemistry, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, United Kingdom., Skakle JMS; Department of Chemistry, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, United Kingdom., Ritter C; Institut Laue Langevin , 6 rue Jules Horowitz, BP 156, F-38042 Grenoble Cedex 9, France., Mclaughlin AC; Department of Chemistry, University of Aberdeen , Meston Walk, Aberdeen AB24 3UE, United Kingdom. |
| Abstrakt: |
The electrical and structural properties of the series Ba 3 Mo 1-x Nb 1+x O 8.5-x/2 (x = 0.0, 0.1, 0.2, 0.3) have been determined. Ba 3 Mo 1-x Nb 1+x O 8.5-x/2 crystallizes in a hybrid of the 9R hexagonal perovskite and palmierite structures, in which (Mo/Nb)O 4 and (Mo/Nb)O 6 units coexist within the structure. Nb substitutes preferentially at the octahedral site so that the ratio of (Mo/Nb)O 4 tetrahedra to (Mo/Nb)O 6 octahedra decreases with increasing x resulting in a reduction in the magnitude of the ionic conductivity from 1.3 × 10 -6 S cm -1 for x = 0.0 to 1.1 × 10 -7 S cm -1 for x = 0.3 at 300 °C. However, upon heating the conductivities of the solid solution converge, which suggests that the unusual thermal structural rearrangement previously reported for Ba 3 MoNbO 8 preserves the high temperature conductivity. The results demonstrate that the presence of (Mo/Nb)O 4 tetrahedra with nonbridging apical oxygen atoms is an important prerequisite for the ionic conduction observed in the Ba 3 MoNbO 8.5 system. |
