Electronic properties of ortho-polymer A1C60 (A = K,Rb) and related phases

1 C₆₀. Its singular structural, magnetic and electrical properties greatly enhanced the study of the AC₆₀ phases (A = Rb, K and \chem{Cs}). We report our continuous wave (cw) ESR results on the structural phase transformations, phase instabilities and the related kinetics of K₁C₆₀. We quantitatively explain the origin of the difference between Rb₁C₆₀ and K₁C₆₀ phase diagrams. The stability of OP-Rb₁C₆₀ together with the narrowness of its homogenous cw-ESR linewidth in the temperature range allow to perform pulsed ESR experiments. Pulsed ESR experiments measure precisely both the electronic spin-spin () and spin-lattice () relaxation times. Above , the equality of and , which are the only contributions to the cw-ESR linewidth, constitutes a convincing evidence of the metallic nature of OP-Rb₁C₆₀. The drastic increase (decrease) of the linewidth () below \valunit{40}{K} is interpreted in terms of an \qut{electronic dimerization}. Received: 12 September 1996/Accepted: 14 November 1996     

Investigation of Paramagnetic Centers in Fullerides A2MC60 and AM2C60 (A = K, Rb, M = Mg, Be)

Paramagnetic centers in heterofullerides with the composition A₂MC₆₀ and AM₂C₆₀ (A = K, Rb, M = Mg, Be) were investigated by the electron spin resonance (ESR) method. It was found that the ESR signal can be interpreted as a composition of two lines with different temperature dependence of ESR absorption magnitude. This gives an evidence of the presence of at least two different types of paramagnetic centers. Centers of the first type behave as localized spins, while the rest can be interpreted as conduction electrons. Authors' address: Vladimir A. Kulbachinskii, Physics Faculty, M. V. Lomonosov Moscow State University, Leninskie Gory, Moscow 119991, Russian Federation     

87Rb NMR investigations on binary and ternary fullerene compounds: Rb3C60, K2RbC60 and Rb2CsC60

Results of¹³C MAS NMR and⁸⁷Rb NMR measurements on Rb₃C₆₀, K₂RbC₆₀ and Rb₂CsC₆₀ are presented. The⁸⁷Rb NMR spectra show generally the same characteristics as already reported by other authors. For the ternary compound the degree of site preferential order of the alkali metal ions agrees with the analysis of X-ray absorption data. Furthermore, in the room temperature⁸⁷Rb NMR spectra of all samples an additional broadened line is detected indicating that at least for the samples prepared from sublimed C₆₀ a considerable amount of the Rb ions is located on sites with symmetry lower than cubic.     

Transport and structural properties of polymerized AC60 (A = K, Rb) under zero and high pressure conditions

60 display transport properties vastly different from their unpolymerized counterparts. We here describe structural (X-ray diffraction and transmission electron microscopy) and dc resistivity measurements of polymerized AC₆₀ (A = K, Rb) at zero and high pressures. The structural and electronic properties are rich, and evidence is found for unusual phase transitions in both materials. Received: 28 October 1996/Accepted: 13 December 1996