Arc-melting synthesis and crystal chemistry of RT2B2(C) (R=rare earth, T=Rh,Co) compounds

The effects of carbon content and rare earth size on the phase stability and crystal chemistry of RT2B2(C) (R=rare earth, T=Rh, Co) compounds have been investigated using arc-melting synthesis and X-ray diffraction. It was found that, for the transition metal cobalt, GdCo2B2Cx compounds could be obtained for x ranging from 0.0 to 1.0. The c-axis of the compound increases significantly with increase in carbon content, while the a-axis decreases slightly. For the transition metal rhodium, however, RRh2B2 could not be obtained for the largest lanthanide, La, or the smallest, Er. With the addition of C to the ternary system, new RRh2B2C compounds have been obtained for R=Y, La to Er, except Eu. The stability of the RRh2B2C phase decreases with decreasing lanthanide size, which can be explained from the rare earth dependence of the crystallographic parameters of the compounds. (orig.)