Synthesis and structural analysis of nonstoichiometric ternary fulleride K_1.5Ba_0.25CsC₆₀

Authors: HAVVA ESMA OKUR KUTAY

Abstract: The existence of cation-vacancy sites in fullerides might lead to long-range ordering and generate a new vacancy-ordered superstructure. The purpose of this work is to search whether or not long-range ordering of vacant tetrahedral sites, namely superstructure emerges in nonstoichiometric K_1.5Ba_0.25CsC₆₀ fulleride. Therefore, K_1.5Ba_0.25CsC₆₀ with cation-vacancy sites is synthesized using a precursor method to avoid inadequate stoichiometry control and formation of impurity phases within the target composition. For this purpose, first, phase-pure K₆C₆₀, Ba₆C₆₀ and Cs₆C₆₀ precursors are synthesized. Stoichiometric quantities of these precursors are used for further reaction with C₆₀ to afford K_1.5Ba_0.25CsC₆₀. Rietveld analysis of the high-resolution synchrotron X-ray powder diffraction data of the precursors and K_1.5Ba_0.25CsC₆₀ confirms that K₆C₆₀, Ba₆C₆₀ and Cs₆C₆₀ are single-phase and they crystallize in a body-centered-cubic structure (Im$\bar{3}$) as reported in the literature. The analysis also shows that K_1.5Ba_0.25CsC₆₀ phase can be perfectly modeled using a face-centered cubic structure. No new peaks appear which could have implied the appearance of a superstructure. This suggests that there is no long-range ordered arrangement of vacant tetrahedral sites in K_1.5Ba_0.25CsC₆₀.

Keywords: Cation-vacancy, solid-state synthesis, A₆C₆₀, nonstoichiometric fullerides

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