Novel rare earth boron-rich solids

A new series of boron-rich solids ReB22C2N (Re: Y, Ho, Er, Tm, Lu)were synt hesized by traditional solid-state reaction. The crystal structure of the r epresentative compound YB22C2N was solved by direct method from powder X-ra y diffraction (XRD) data and transmission electron microscope (TEM) analysi s, The unit cell of the new structure is rhombohedral with space group R-3m (No, 166), lattice constant a = b = 5.623(0) Angstrom and c = 44.785(3) An gstrom with six formula units in one unit cell, The atoms of boron in the s olids, like most of the boron-rich solids, exist with icosahedral and octah edral clusters, and the whole crystal shows a layered structure, The interc onnected nine layers of icosahedron and three layers of octahedron in a uni t cell build the whole framework of the new phase and rare earth metal atom s reside in voids of the octahedron layers. The neighboring icosahedral lay ers link through C-B-C chains besides the direct bonding of B-B, Both exper imental and structural analysis indicated that the nitrogen atoms in the ne w phase can be replaced with carbon. (C) 2001 Academic Press.