STRUCTURE AND MAGNETIC-PROPERTIES OF 6-LAYERED HEXAGONAL OXIDES BA(3)CR(2)MO(9) (M=MO AND W)

Structural analysis and measurement of magnetic susceptibility were ca rried out for the 6H-type hexagonal compounds Ba(3)Cr(2)MO(9) (M = Mo and W). The space groups of Ba3Cr2MoO9 and Ba3Cr2WO9 were determined b y Rietveld analysis of powder X-ray diffraction data to be P6(3)/mmc a nd <P(6)over bar 2c>, respectively. Chromium ions were found to occupy the centers of face-shared octahedra, with tungsten or molybdenum ion s at the centers of corner-shared octahedra. The magnetic susceptibili ties of Ba3Cr2MoO9 and Ba3Cr2WO9 were explained using the two-sublatti ce and dimer models, respectively; the difference may be due to the di fference in the valence states of Cr and Mo in Ba3Cr2MoO9 and Cr and W in Ba3Cr2WO9. (C) 1995 Academic Press, Inc.