The crystal structure of La(3)Mo(4.33)Al(0.67)O(14) and the electronic structure of La(3)Mo(4)XO(14) X=Si;Mo(1/3)Al(2/3); Al(1/2)V(1/2).
01 January 1986
Black needles of La(3)Mo(4.33)Al(0.67)O(14) were prepared by electrolytic reduction at 1100C of a melt containing Na(2)MoO (4), MoO(3) and La(2)0(3) held in an alumina crucible. The compound is isomorphous with La(3)Mo(4)SiO(14), crystallizing in space group pnma with a=17.750(3)angstroms, b=5.6600(9)angstroms, c=11.070(2)angstroms, V=1112.1(6)angstroms(3), and Z=4. The structure was refined by full-matrix least squares to R(F)=3. 43%, R(WF)=3.45%, with 1912 independent reflections. As in La(3)Mo(4)SiO(14), the structure contains Mo(3)O(13) clusters and chains of edge-sharing MoO(6) octahedra with alternately short (2.535angstroms) and long (3.167angstroms) Mo-Mo distances, but unlike La(3)Mo(4)SiO(14), the tetrahedral silicon is replaced by a random distribution of 1/3 Mo and 2/3 Al. Electrical conductivity measurements show that La(3)Mo(4)SiO(14) and La (3)Mo(4)Al(2/3)Mo(1/3)O(14) are both highly anisotropic semiconductors with the easy direction of conduction being parallel to the chain cluster units.