SYNTHESIS OF THE GDCO2B2CX (X=0-SIMILAR-T O-1) AND STUDY ON THE CHANGING OF THE CRYSTAL-STRUCTURE WITH CARBON CONTENT, X

GdCo2B2Cx (x = 0-1) has been synthesized to study the role of C in the formation of a new quaternary compounds RT2B2C (R = rare earth, T = t ransition metal); RT2B2C belongs to a tetragonal system with ThCr2Si2 derivative type, Samples of GdCo2B2Cx (x = 0, 0.25, 0.50, 0.75 and 1.0 0) were prepared by the arc-melting synthetic method, According to bac kscattered SEM study, the obtained compound of tetragonal phase was ob served as rectangular, narrow-ribbon and wide-ribbon for x = 0, 0.25-0 .75 and 1.00 in GdCo2B2Cx, respectively, The lattice parameter a sligt ly decreased,while the lattice parameter c and the unit cell volume in creased appreciably with increasing x in GdCo2B2Cx. This result shows that C element serves to expand the entire unit cell in the shape of a square column composed of R atoms (eight at the corners) especially a long the c-direction, and permit T atoms, which are too large for the normal lattice, to join in combination. The role of C to form the quat ernary borocarbides RT2B2C has been demonstrated.