Crystal Structure and Electronic Band Structure of LaTe2

Abstract

The observation of superstructure reflections indicating a (2×2×1) 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 β=90.04(1)° (Z=8). Compared to the anti-Fe2As basis structure, the polyanionic square [44] 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 ≈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 Γ 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 χmol≈1.1×10−4 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.