Phase Transition in Cu-Intercalated Misfit-Layer Compounds

✍ Scribed by Youichi Ohno

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 378 KB
• Volume: 134
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7542

✦ Synopsis

The Cu-intercalated misfit-layer compounds Cu x (MS) 1؉y (NbS 2 ) 2 (M ‫؍‬ Ce and Sm), which consist of regularly stacked Cu, MS, and NbS 2 layers with incommensurate intergrowth structure, are studied by means of X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (EELS). The Nb N 2,3 inner-shell electron energy loss spectroscopy (ISEELS) spectra and the valence-band XPS spectra show charge transfer from Cu and MS layers to NbS 2 layers. A strong Cu-Nb interaction and a drastic change of the electronic structure are found, which may result from the change of the crystal structure within a NbS 2 sublattice from the 3R polytype at lower Cu concentration to the 2H and/or the 4H polytypes at higher Cu concentration. In the 3R polytype, Nb atoms sit in the center of a trigonal prism with six S atoms at the corners whereas in the 2H and/or the 4H polytypes, all or half of the Nb atoms are surrounded octahedrally by six S atoms. An intercalated Cu layer donates a larger number of electrons to NbS 2 layers than a MS layer at the maximum uptake of x ‫؍‬ 0.67. Finally, the Nb d z 2 band is completely filled with two electrons per Nb atom and the rigidband model is no longer valid.