Structural aspects of deposited niobium nanoclusters approximately 10 nm in size have been explored by means of high-resolution transmission electron microscopy. The niobium clusters have a bcc structure and a crystal habit of rhombic dodecahedron. In situ heating up to similar to800 degreesC revealed a resistance to high temperatures, in the sense that the cluster habit is preserved. However, the internal structural order of the clusters is altered due to formation of niobium oxide domains within the clusters. Coalescence does not occur even at the highest temperatures, which is attributed to the presence of facets and the occurrence of oxidation during heat treatment. (C) 2003 American Institute of Physics.