Regensburg 2007 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 25: Electronic properties II
MM 25.6: Talk
Wednesday, March 28, 2007, 16:00–16:15, H6
Boron/Carbon ordering in layered MB2C2 compounds — Sergii Khmelevskyi, Peter Mohn, and •Josef Redinger — Inst. f. Allgemeine Physik, Vienna University of Technology, Getreidemarkt 9/134, A-1060 Vienna, Austria
Superconductivity in layered diboride dicarbide materials has been observed in YB2C2 and LuB2C2, but not in LaB2C2. Starting from our previous ab-initio DFT work on YB2C2 [1], where we showed that metallic conductivity in the stable P4/mbm structure is due to Y d-bands partially hybridized with pz-states from the boron-carbon planes, we present new results on the electronic structure of various layered boro-carbides such as CaB2C2, ScB2C2, SrB2C2, YB2C2, LaB2C2 and LuB2C2. We concentrate on the ordering of B and C in the layers and the impact of d−p hybridization which seems to decide the actually observed structures. Except ScB2C2 which favours a 5-7 ring boron-carbon network (Pbma) all the others prefer 4-8 ring networks with alternating B and C atoms within the boron-carbon layer and a B-B (C-C) - like (P4/mbm) or B-C (C-B) - like (I4/mcm) layer stacking along the c-axis. Apparently, d−p hybridization (YB2C2, LaB2C2 and LuB2C2) tips the scale in favour of P4/mbm, whereas CaB2C2 and SrB2C2 remain I4/mcm.
[1] S. Khmelevskyi, P. Mohn, J. Redinger, and H. Michor, Supercond. Sci. Technol. 18, 422-426, (2005).