Ternary rare earth metal boride carbides containing two-dimensional boron-carbon network: The crystal and electronic structure of R2B4C (R = Tb, Dy, Ho, Er)

摘要

The ternary rare earth boride carbides R2B4C (R = Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy2B4C has been determined from single-crystal X-ray diffraction data. It crystallizes in a new structure type in the orthorhombic space group Immm (a = 3.2772(6) angstrom, b = 6.567(2) angstrom, c = 7.542(1) angstrom, Z = 2, R1= 0.035 (wR(2) = 0.10) for 224 reflections with I-o > 2 sigma(I-o)). Boron atoms form infinite chains of fused B-6 rings in [100] joined with carbon atoms into planar, two-dimensional networks which alternate with planar sheets of rare earth metal atoms. The electronic structure of Dy2B4C was also analyzed using the tight-binding extended Huckel method. (C) 2007 Elsevier Inc. All rights reserved.