Crystal structure and electronic band structure of LaTe2

摘要

The observation of superstructure reflections indicating a (2 x 2 x 1) supercell of the simple anti-Fe2As structure type made it necessary to redetermine the crystal structure of LaTe2 by single-crystal analysis. In contrast to former investigations revealing tetragonal or orthorhombic symmetry, our analysis showed that LaTe2 crystallizes monoclinic in space group P1c1 with the lattice parameters a = 919.0(1) pm, b = 910.7(1) pm, c = 907.0(1) pm, and beta = 90.04(1)degrees (Z = 8), Compared to the anti-Fe2As basis structure, the polyanionic square [4(4)] nets are distorted in LaTe2 into herringbone patterns of dimer pairs with interatomic distances of 298.7 and 303.6 pm within the dimers, Electronic band structure calculations with the LMTO-ASA method revealed that by the distortion an indirect band gap of approximate to 0.2 eV between bonding and antibonding dimer Te 5p states opens up at the Fermi level. But due to a weak direct La-La interaction a single La 5d band is lowered in energy around the Brillouin zone center Gamma and thus is responsible for the metallic conductivity of this material. This finding is in agreement with magnetic susceptibility data, revealing after diamagnetic correction a temperature-independent Pauli paramagnetism chi mol approximate to 1.1 x 10(-4) emu mol(-1) at 300 K and recordings of the fundamental optical absorption in the energy range of 0.05-1.33 eV, which gave no indications for a band gap in this range. (C) 2000 Academic Press. [References: 29]