Crystal structure and Ce valence variation in the solid solution CeRh_3-xPdxB_0.5

Crystal structure and physical properties have been studied in the solid solution CeRh_3-xPdxB_0.5 (x = 0, 0.5, 1.2, 1.5, 1.7, 2.5, 3) in as-cast state by x-ray powder diffraction and scanning and high-resolution electron microscopy, as well as by low-temperature measurements of the magnetic susceptibility and specific heat. X-ray powder patterns of the alloys were indexed on the basis of a cubic primitive AuCu3 lattice throughout the entire solution showing a monotonous increase in three regimes. For 0x1.5, the volume increase corresponds merely to the substitution of Rh by Pd atoms, the sizes of which are rather close. In this regime the tetravalent character of cerium is unaffected. For x < 1.5, the lattice expansion becomes enhanced and is thus attributed to a gradual valence change of the Ce atoms (an intermediate valence regime). Finally, for x < 2.4, the system shows a predominant trivalent behavior. In this region, the specific heat coefficient reaches a value of 4.4 J mol-1 K2, two orders of magnitude larger than that in the Rh-rich border. Selected area electron diffraction patterns of the CeRh_3-xPdxB_0.5 compounds revealed the appearance of -type superstructures and satellite reflections with respect to the parent AuCu3 structure. Whereas the -type superstructure is confined to the Rh-rich part of the solid solution, satellite reflections are observed throughout the solid solution and hint towards the existence of a domain structure enclosed by anti-phase boundaries.