HIGH-RESOLUTION ELECTRON-MICROSCOPY INVESTIGATIONS ON THE REAL STRUCTURE OF IN5MO18O28

In5Mo18O28, a reduced ternary molybdenum oxide in the series Mn+/-delt aMO4n + 2O6n + 4 with n = 4, is a cluster compound containing Mo4n + 2 O8n + 10 clusters with n = 4 trans edge-sharing molybdenum octahedra. A crystal of the compound was investigated by high-resolution electron microscopy (HREM) and related methods, and a comprehensive descriptio n of real-structure phenomena is given, These phenomena include: (i) t he existence of two ordered polytypes (modifications), 1M and 2O, whic h may intergrow with each other, (ii) stacking disorder, and (iii) pol y-synthetic twinning of the 1M polytype, In both ordered polytypes, or dered and disordered chemical intergrowth of Mo4n + 2O8n + 10-cluster layers with n = 3, 5, and 6 is observed, Structure models were generat ed for both modifications in order to hare available sets of input dat a for the simulation of HREM images and electron diffraction intensiti es, Discrepancies between the results obtained by electron microscopy and by recent single-crystal x-ray structure analysis are discussed. ( C) 1997 Academic Press.