Syntheses, crystal and electronic structure, and some optical and transport properties of LnCuOTe ( Ln=La, Ce, Nd)
Abstract
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) Å, c=9.3260(16) Å, V=162.75(4) Å3 for LaCuOTe; a=4.1497(3) Å, c=9.3090(10) Å, V=160.30(2) Å3 for CeCuOTe; and a=4.1056(9) Å, c=9.332(4) Å, V=157.30(8) Å3 for NdCuOTe. The structure of LnCuOTe ( Ln=La, Ce, Nd) is composed of alternating PbO-like [ Ln2O 2] and anti-PbO-like [Cu 2Te 2] 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 LaCuO Q ( Q=S, Se, Te). In LaCuOTe, Cu 3 d and Te 5 p orbitals dominate the states near the valence band maximum; the states near the conduction band minimum are composed of Cu 4 s, Te 5 p, and La 5 d orbitals. The larger dispersion of Cu 3 d orbitals and the presence of Te 5 p orbitals near the valence band maximum are responsible for the larger hole mobility of LaCuOTe compared to LaCuOS and LaCuOSe.
- Publication:
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Journal of Solid State Chemistry France
- Pub Date:
- January 2007
- DOI:
- 10.1016/j.jssc.2006.09.014
- Bibcode:
- 2007JSSCh.180...62L