An unusual six-layered structure in gadolinium and samarium monoxides has been identified employing electron-diffraction methods. This structure is derived from the zincblende-type gadolinium or samarium monoxide. The lattice parameters of the 6R structure are aR = bR = 2a0√2, CR = 2a0√3 (referred to hexagonal axes), where a0 is the lattice parameter of the fundamental zincblende-type gadolinium or samarium monoxide unit cell. A sixlayered rhombohedral structure consisting of close-packed structural layers is usually not possible since it is equivalent to face-centered cubic structure. The detailed atomic structure of the 6R variant has been determined. It is further shown that the stabilization of this structure is due to existence of nonstoichiometric oxygen layers in the sequence forming the 6R structure.
The monoxides of the rare earth metals are currently receiving attention because of the possibility of their being ‘n’ or ‘p’ type semiconductors [6]. Unlike the R2O3 type sesquioxides whose structures and existence have been well established, very little details regarding the existence, structure, and defect substructure of monoxides are available. The present investigation describes the existence and structural crystallography and defect substructure of gadolinium and samarium monoxides and of their reduced variants. The gadolinium and samarium monoxides were prepared in the form of thin film and were found to have zinc blende type structures with lattice parameters equal to (5.24 ± 0.05) Å and (5.15 ± 0.05) Å respectively. Annealing of the original material has been found to result in the formation of superlattices and the accompanying domain substructures. The superlattices as described on hexagonal axes have rhombohedral unit cells with lattice parameters \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm R} = 2\,a_{\rm c} \sqrt 2 $\end{document} and \documentclass{article}\pagestyle{empty}\begin{document}$ c_{\rm R} = 2\,a_{\rm c} \sqrt 3 $\end{document} (ac being the lattice parameter of the fundamental zinc sulphide type unit cell). The detailed structure analysis of the superlattices has been carried out and it has been found that the superlattices are formed by the ordered arrangement of oxygen vacancies in the parent lattices, the nonstoichiometric variants are of the form ROx where R = Gd, Sm and x = 0.656. Den Monoxiden der Seltenen Erden wird wegen der Möglichkeit, „n”︁- oder „p”︁-leitende Halbleiter zu bilden, laufend stärkere Beachtung geschenkt [6]. Im Gegensatz zu den R2O3-Sesquioxiden, deren Struktur und Existenz gut bekannt ist, sind nur wenige detaillierte Angaben über die Existenz, Struktur und Defektsubstruktur der Monoxide erhältlich. Die vorgelegte Untersuchung beschreibt die Existenz und strukturelle Kristallographie und Defektsubstruktur von Gadolinium- und Samariummonoxid und deren reduzierte Varianten. Die Gadolinium- und Samariummonoxide wurden in Form dünner Schichten erhalten. Es wurde gefunden, daß sie Zinkblendestruktur besitzen mit Gitterparametern von (5,24 ± 0,05) bzw. (5,15 ± 0,05) Å. Temperung von ursprünglichem Material ergab die Bildung von Übergittern und der begleitenden Domänen-Substrukturen. Die Übergitter, durch hexagonale Achsen beschrieben, haben rhomboedrische Einheitszellen mit den Gitterparametern \documentclass{article}\pagestyle{empty}\begin{document}$ a_{\rm R} = 2\,a_{\rm c} \sqrt 2 $\end{document} und \documentclass{article}\pagestyle{empty}\begin{document}$ c_{\rm R} = 2\,a_{\rm c} \sqrt 3 $\end{document} (ac ist der Gitterparameter der fundamentalen Einheitszelle vom Zinksulfidtyp). Es wurde eine genaue Strukturanalyse der Übergitter durchgeführt und gefunden, daß die Übergitter durch die geordnete Anordnung von Sauerstofflücken im Gitter gebildet werden, wobei die nichtstöchiometrischen Varianten von der Form ROx sind, mit R = Gd, Sm und x = 0,656.
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