Synthesis and structural analysis of nonstoichiometric ternary fulleride K1.5Ba0.25CsC60

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-15 Ba0.25CsC60 fulleride. Therefore, K1.5Ba0.25CsC60 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, BA(6)C(60) and Cs-6 C-60 precursors are synthesized. Stoichiometric quantities of these precursors are used for further reaction with C-60 to afford K1.5Ba0.25CsC60. Rietveld analysis of the high-resolution synchrotron X-ray powder diffraction data of the precursors and K1.5Ba0.25CsC60 confirms that K6C60, Ba6C60 and Cs6C60 are single-phase and they crystallize in a body-centered-cubic structure (Im (3) over bar) as reported in the literature. The analysis also shows that K1.5Ba0.25CsC60 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 K1.5Ba0.25CsC60.