Crystal structure of a Cu3Au-type compound CeRh3B0.5 studied by high-resolution electron microscopy

We have examined the structure of a Cu3Au-type compound CeRh3B0.5 by means of electron diffraction and high-resolution electron microscopy. The observed electron diffraction patterns of CeRh3B0.5 show the appearance of 1/2 1/2 1/2-type superlattice reflections and fine satellite reflections around all reflections. These features have not been detected by X-ray powder diffraction study. The new ordered structure producing the superlattice reflections belongs to a tetragonal system, space group I4/mmm   (No. 139) and cell parameters of at=bt=ac2=0.5795 nm and ct = 2cc = 0.8196 nm. The proposed model is characterized by ordering of both B atoms and Rh octahedrons. The observed high-resolution image taken with a diffraction pattern showing the satellite reflections along the [0 1 1] direction shows a domain structure with size of about 3 nm, and a lattice modulation and some edge dislocations have been observed at boundaries between the domains. It is suggested that the anomalous behavior of hardness in CeRh3Bx is caused by the appearance of this modulated structure.