Reduced molybdenum-niobium oxides. 1. Synthesis, structure, and physical properties of K[sub 2]Mo[sub 4]Nb[sub 3]O[sub 20]

Journal Article · Wed Sep 29 00:00:00 EDT 1993 · Inorganic Chemistry; (United States)

DOI:https://doi.org/10.1021/ic00072a025· OSTI ID:5091502

Chen, S C; Wang, B; Greenblatt, M ^[1]

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1. Rutgers, The State Univ. of New Jersey, Piscataway, NJ (United States)

K[sub 2]Mo[sub 4]Nb[sub 3]O[sub 20] crystallizes in the orthorhombic system, space group Pbcm (No. 57). The unit cell dimensions are a = 4.0176(7) [angstrom], b = 17.891(4) [angstrom], c = 21.825(3) [angstrom], V = 1568.7(5) [angstrom][sup 3], and Z = 4. Because of the inability to distinguish between the Mo and Nb atoms by X-ray diffraction, the structure of K[sub 2]Mo[sub 4]Nb[sub 3]O[sub 20] was refined on the basis of K[sub 2]Mo[sub 7]O[sub 2]. The final residual indexes are R = 0.035 and R[sub w] = 0.041, with 717 observed reflections (I > 3[sigma](I)) and 90 variable parameters. The structure of K[sub 2]Mo[sub 4]Nb[sub 3]O20 consists of pentagonal clusters of polyhedra that are linked together via bridging, corner-sharing octahedra in the bc plane. These layers stack along the a axis, forming pentagonal columns and octahedral strings. The pentagonal cluster of polyhedra contains an MO[sub 7] pentagonal bipyramid that shares equatorial edges with five MO[sub 6] octahedra, forming a star-shaped cluster of polyhedra (M - Mo, Nb). The K ions are located in the one-dimensional S-shaped tunnels, running along the a axis, created by the network of polyhedra. K[sub 2]Mo[sub 4]Nb[sub 3]O[sub 20] is an electronic insulator and exhibits ionic conductivity at temperature above 150 [degrees]C. The temperature dependence of the magnetic susceptibility of K[sub 2]Mo[sub 4]Nb[sub 3]O[sub 20] does not follow Curie-Weiss law behavior. A magnetic moment of 1.56 [mu][sub B]/mol calculated at 250 K is consistent with one localized electron per formula unit estimated from the valence count.

• OSTI ID: 5091502
• Journal Information: Inorganic Chemistry; (United States), Vol. 32:20; ISSN 0020-1669
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
MOLYBDENUM OXIDES
CRYSTAL STRUCTURE
PHYSICAL PROPERTIES
NIOBIUM OXIDES
POTASSIUM OXIDES
CHEMICAL PREPARATION
LATTICE PARAMETERS
ORTHORHOMBIC LATTICES
TEMPERATURE RANGE 0000-0013 K
TEMPERATURE RANGE 0013-0065 K
TEMPERATURE RANGE 0065-0273 K
ALKALI METAL COMPOUNDS
CHALCOGENIDES
CRYSTAL LATTICES
MOLYBDENUM COMPOUNDS
NIOBIUM COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
POTASSIUM COMPOUNDS
REFRACTORY METAL COMPOUNDS
SYNTHESIS
TEMPERATURE RANGE
TRANSITION ELEMENT COMPOUNDS
360202* - Ceramics
Cermets
& Refractories- Structure & Phase Studies
360204 - Ceramics
Cermets
& Refractories- Physical Properties