Crystal structure, magnetic properties and band gap measurements of NdTe2- x (x=0.11(1))

Abstract

Abstract As for the homologous La, Ce and Pr compounds, the X-ray diffraction single-crystal structure analysis of NdTe2 (prepared by chemical vapor transport reactions in the presence of traces of iodine) also revealed superstructure reflections, but indicating a (3x4x2) supercell of the basic anti-Fe2As type instead of a (2x2x1) supercell as for LaTe2 or a (2x2x2) supercell as for CeTe2 and PrTe2. NdTe2 crystallizes orthorhombic with the lattice parameters a = 1328.9(1) pm, b = 1767.7(2) pm and c = 1806.9(2) pm (Z = 48) in space group Amm2. Analysis by ICP-OES as well as density measurements revealed a nonstoichiometric composition (ICP-OES: NdTe1.90(2); X-ray diffraction: NdTe1.89(1)), whereas the other compounds of this series, LaTe2, CeTe2 and PrTe2, showed no defects in the tellurium sublattice. Compared to the basic anti-Fe2As structure type, the differences of this new structure lie entirely in the topology of the polyanionic square nets. Due to the presence of distortions and defects, the sheets may be regarded as revealing several different canonical entities, which are assumed by emphasizing interatomic distances below a certain limit (305 pm). These entities are [Te2] dimers, square-shaped [Te8] rings and, to a small amount, even more complicated fragments. All in all the distortions lead to a semiconducting compound (band gap ΔE = 0.14 eV), which obeys the Curie-Weiss law and reveals even at T = 2 K no indications for a magnetic ordering.