SYNTHESIS AND CHARACTERIZATION OF NEW QUATERNARY BOROCARBIDES RRH2B2C(R = RARE-EARTH)

Arc-melting syntheses of RRh2B2C were carried out for all lanthanide e lements except promethium. X ray diffraction revealed that new compoun ds exist for R = Y, La-Er (except Eu), and the stability of RRh2B2C de creases for the smaller lanthanide, The tetragonal a-axis of RRh2B2C w as found to contract as R goes from La to Er. The c-axis, however, exp ands slightly, In accordance with the lattice parameter change, intera tomic distances between Rh atoms decrease significantly from 2.7623 An gstrom in LaRh2B2C to 2.6552 Angstrom in ErRh2B2C. The reduced stabili ty of the RRh2B2C phase for the smaller rare earth is explained by the change in the crystallographic parameters with the size of R. (C) 199 7 Academic Press.