Crystal structure of La/sub 3/Mo/sub 4. 33/Al/sub 0. 67/O/sup 14/ and the electronic structure of La/sub 3/Mo/sub 4/XO/sub 14/ (X = Si; Mo/sub 1/3/Al/sub 2/3/; Al/sub 1/2/V/sub 1/2/)
Black needles of La/sub 3/Mo/sub 4.33/Al/sub 0.67/O/sub 14/ were prepared by electrolytic reduction at 1100/sup 0/C of a melt containing Na/sub 2/MoO/sub 4/, MoO/sub 3/, and La/sub 2/O/sub 3/, held in an alumina crucible. The compound is isomorphous with La/sub 3/Mo/sub 4/SiO/sub 14/, crystallizing in space group Pnma with a = 17.750(3) A, b = 5.6600(9) A, c = 11.070(2) A, V = 1112.1(6) A/sup 3/, and Z = 4. The structure was refined by full-matrix least squares to R/sub F/ = 3.43%, R/sub WF/ = 3.45%, with 1912 independent reflections. As in La/sub 3/Mo/sub 4/SiO/sub 14/, the structure contains Mo/sub 3/O/sub 13/ clusters and chains of edge-sharing MoO/sub 6/ octahedra with alternatively short (2.535 A) and long (3.167 A) Mo-Mo distances, but unlike La/sub 3/Mo/sub 4/SiO/sub 14/, the tetrahedral silicon is replaced by a random distribution of 1/3 Mo and 2/3 Al. Electrical conductivity measurements show that La/sub 3/Mo/sub 4/SiO/sub 14/ and La/sub 3/Mo/sub 4/Al/sub 2/3/Mo/sub 1/3/O/sup 1//sub 4/ are both highly anisotropic semiconductors with the easy direction of conduction being parallel to the chain cluster units. Semiempirical bond length-bond strength calculations lead to the conclusion that the valences of the molybdenums in both the chains and the clusters are remarkably similar. This coupled with the observed diamagnetism of the silicon compound can best be explained in terms of an electronic band structure rather than a localized model. 22 references, 5 figures, 6 tables.
- Research Organization:
- Rider College, Lawrenceville, NJ
- OSTI ID:
- 5680028
- Journal Information:
- J. Solid State Chem.; (United States), Vol. 62:2
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
ALUMINIUM OXIDES
CRYSTAL STRUCTURE
ELECTRICAL PROPERTIES
LANTHANUM OXIDES
MOLYBDENUM OXIDES
SILICON OXIDES
VANADIUM OXIDES
BAND THEORY
BOND LENGTHS
ALUMINIUM COMPOUNDS
CHALCOGENIDES
DIMENSIONS
LANTHANUM COMPOUNDS
LENGTH
MOLYBDENUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
REFRACTORY METAL COMPOUNDS
SILICON COMPOUNDS
TRANSITION ELEMENT COMPOUNDS
VANADIUM COMPOUNDS
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