Fullerenes Doped with Thallium Alloys
- PDF / 279,114 Bytes
- 5 Pages / 420.48 x 639 pts Page_size
- 103 Downloads / 204 Views
FULLERENES DOPED WITH THALLIUM ALLOYS M. KRAUS-, M. BAENITZ-, S. G.ARTNER-, H.M. VIETH-, H. WERNER", R. SCHLOGL", W. KRATSCHMER-". M. KANOWSKI', V. THOMMEN..., H.-J. GUNTHERODT..., AND K. LUDERS"
"Institut
ffir Experimentalphysik, Freie Universitit Berlin, Arnimallee 14, W-1000 Berlin 33, Germany "'Institut fiur Anorganische Chemie der Universitat, Niederurseler Hang, W-6000 Frankfurt am Main, Germany ""Max-Planck-Institut ffir Kernphysik, Postfach 103980, W-6900 Heidelberg, Germany .. Institut fiir Physik, Universitit Basel, Klingelbergstr. 82, CH-4056 Basel, Switzerland ABSTRACT Prompted by earlier work showing that graphite intercalation compounds form superconducting ternary compounds in which thallium plays an important role C60 has been doped with Tl-alloys. Results of dc-magnetization, ac-susceptibility, X-ray analysis and NMR investigations will be presented. INTRODUCTION The occurrence of superconductivity in C 60 doped with alkali metals like potassium [1-4] and rubidium [5-6] is now well established. In order to obtain a larger variety of superconducting C60 compounds and to increase the critical temperature T, we have intercalated C60 using binary thallium alloys. Combinations of the C60 molecule with alkali metals and a third component (e.g. thallium, bismuth or mercury [4,7-10]) are reported to show superconductivity. Investigations of doped C60 of composition A3C 60 (where A is KI, Rb, Cs or a mixture of these) revealed that T, increases monotonically with the size of the unit cell [11,12]. Depending on the degree of ionisation thallium could therefore be a suitable codopant to raise T,. In contrast to our previous findings [7,8] and to those of Kelty et al. [9] where T, seems not to be altered, Iqbal et al. [4] claim the observation of T, values up to 48 K in C60 samples doped with a rubidium-thallium alloy. The latter results, however, have not been reproduced yet independently. PREPARATION C60 molecules were synthesized from the soot of evaporated graphite as described earlier [13]. The C60 powder used for preparation of all samples investigated in this work contains about 10% C 70 . By heating the respective amounts of metals sealed in pyrex glass tubes for typically 1 h alloys of various compositions listed in Table I were prepared. Based on early ideas suggesting a similarity of doped fullerenes and intercalated graphite we used KTl1 .5- and RbTlI.s-alloys in our first doping experiments. An annealing temperature of 340°C and an alloy composition of KTl1 .s has been used successfully to obtain first stage KT 11.5 graphite intercalation compounds whereas higher annealing temperatures applied at thallium-richer compositions resulted in multi phase samples or stage two compounds [14]. Thallium-poorer alloys than KT 1L.5 revealed only binary graphite intercalation compounds [14]. In contrast to this, C60 powder samples being doped with alloys consisting of a lower relative amount of TI to Rb were more likely to provide a rise in T, according to the findings of Iqbal et al. [4]. Therefore, in the
Data Loading...
