Ternary rare earth metal boride carbides containing two-dimensional boron–carbon network: The crystal and electronic structure of R2B 4C ( R=Tb, Dy, Ho, Er)

Abstract

The ternary rare earth boride carbides R 2B 4C ( R=Tb, Dy, Ho, Er) have been synthesized by reacting the elements at temperatures between 1800 and 2000K. The crystal structure of Dy 2B 4C 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) Å, b=6.567(2) Å, c=7.542(1) Å, Z=2, R1=0.035 (w R 2=0.10) for 224 reflections with I o>2 σ( 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 Dy 2B 4C was also analyzed using the tight-binding extended Hückel method.