B. Albert et K. Schmitt, CaB2C2: Reinvestigation of a semiconducting boride carbide with a layered structure and an interesting boron/carbon ordering scheme, INORG CHEM, 38(26), 1999, pp. 6159-6163
Calcium diboride dicarbide, CaB2C2, was synthesized as a crystalline powder
and investigated by electron energy loss spectroscopy, X-ray powder diffra
ctometry, conductivity measurements, and LMTO band structure calculations.
A new structure model was derived, and the crystal structure was refined by
Rietveld methods in the tetragonal space group 14/mcm (No. 140, a = 537.33
(1) pm and c = 741.55(2) pm, Z = 4). The boron and carbon atoms are well or
dered within layers consisting of four- and eight-membered rings. A convinc
ing coloring scheme is proven by the detection of a superstructure reflecti
on. An earlier assignment of the compound into the LaB2C2 structure family
(space group P (4) over bar 2c or P4(2)/mmc, respectively) has been shown t
o be incorrect. LMTO band structure calculations suggest semiconducting beh
avior for CaB2C2, which has been confirmed by conductivity measurements.