Syntheses, crystal and electronic structure, and some optical and transport properties of LnCuOTe (Ln = La, Ce, Nd)

Three new compounds, LaCuOTe, CeCuOTe, and NdCuOTe, have been synthesized from the respective rare-earth elements, CuO, and a KI flux at 1023 K. The compounds, which have the ZrSiCuAs structure type, are isostructural to LaCuOS, and crystallize in space group P4/nmm of the tetragonal system with two formula units in cells of dimensions at 153 K of a = 4.1775(5) A, c = 9.3260(16) angstrom, V = 162.75(4) angstrom(3) for LaCuOTe; a = 4.1497(3) angstrom, c = 9.3090(10) angstrom, V = 160.30(2) angstrom(3) for CeCuOTe; and a = 4.1056(9) angstrom, c = 9.332(4) angstrom, V = 157.30(8) angstrom(3) for NdCuOTe. The structure of LnCuOTe (Ln = La, Ce, Nd) is composed of alternating PbO-Iike [Ln(2)O(2)] and anti-PbO-like [Cu2Te2] layers stacked perpendicular to [0 0 1]. The experimental optical band gaps of LaCuOTe and NdCuOTe are 2.31 and 2.26 eV, respectively. At 298 K the electrical conductivity of LaCuOTe is 1.65 S/cm and the Hall mobility is + 80.6 cm(2) V-1 s(-1). The positive values of the Seebeck and Hall coefficients indicate p-type electrical conduction. First-principles theoretical calculations were performed on LaCuOQ (Q = S, Se, Te). In LaCuOTe, Cu 3d and Te 5p orbitals dominate the states near the valence band maximum; the states near the conduction band minimum are composed of Cu 4s, Te 5p, and La 5d orbitals. The larger dispersion of Cu 3d orbitals and the presence of Te 5p orbitals near the valence band maximum are responsible for the larger hole mobility of LaCuOTe compared to LaCuOS and LaCuOSe. (c) 2006 Elsevier Inc. All rights reserved.