Microstructure and metal-insulator transition in single crystalline KMo4O6

Abstract

High quality KMo 4 O 6 single crystals with tetragonal structure (space group P4/mbm) have been prepared by fused salt electrolysis. The crystals were studied by scanning electron microscopy (SEM), X-ray diffractometry, electrical resistivity, and magnetization measurements. X-ray powder diffraction patterns and SEM have given some information on the growth of single crystals. Electrical resistivity as a function of temperature shows that the KMo 4 O 6 compound is a bad metal with resistivity change of approximately 30% in the temperature range from 2 to 300K. A metal-insulator transition (MIT), observed at approximately 110K, has been also confirmed for this material. Magnetization as a function of temperature agrees with previous report, however a magnetic ordering has been observed in M(H) curves in the whole temperature range.

LiMo8O10: Polar Crystal Structure with Infinite Edge-Sharing Molybdenum Octahedra

“…The semiconducting behavior is in contrast to the expected metallic behavior based on the strong infinite Mo–Mo bonding, which has been observed in AMo 4 O 6 (A = Na and In) and Mn 1.5 Mo 8 O 11 compounds with a similar edge-sharing Mo 6 octahedra feature. ,, However, the metal-to-insulator transitions occur at 118–120 and 50 K for KMo 4 O 6 and SnMo 4 O 6, respectively. ,, R 4 Mo 18 O 32 (R = Y and Gd–Yb) with Mo 2 , Mo 4 , and Mo 6 clusters also show metal-to-insulator transitions in the range of 70–120 K . The semiconducting behavior is also reasonable considering that there are Mo–O–Mo bonding between chains and O–Li–O bonding between the layers, in addition to strong Mo–Mo bonding within the infinite chains of Mo 4 O 5 clusters.…”

“…They have infinite chains of Mo 4 O y cluster units containing condensed edge-sharing Mo 6 octahedra with Mo–Mo metal bonding. Reported examples include AMo 4 O 6 (A = Na, K, In, and Sn; space group P 4/ mbm ), − Sc 0.75 Zn 1.25 Mo 4 O 7 (space group Imam ), isostructural Ti 0.5 Zn 1.5 Mo 4 O 7 , GaMgMo 4 O 7 , Fe 2 Mo 4 O 7 , AMo 8 O 10 (A = Li, Zn; space group I 4 1 md ), R 4 Mo 4 O 11 (R = Y, Nd, and Sm-Tm; space group Pbam ), and Mn 1.5 Mo 8 O 11 (space group P 2 1 / a and P 2 1 / n ). , The metallic behavior in AMo 4 O 6 (A = Na and In) and Mn 1.5 Mo 8 O 11 ,, and the metal-to-insulator transition in AMo 4 O 6 (A = K and Sn), ,, have been attributed to the infinite Mo–Mo bonding chains in the crystal structure. Among these reported compounds, AMo 4 O 6 (A = Na and K) and LiMo 8 O 10 belong to ternary alkali metal molybdenum oxides, and LiMo 8 O 10 is the only one that adopts a polar space group.…”