Superconducting properties of new heterofullerides

Abstract

Superconducting properties of new heterofullerides synthesized for the first time AnMmHgxC60 (A = K, Rb, Cs; M = Be, Mg, B, Al, Ga, In; n = 1, 2; m = 1, 2; x ≪ 1) were investigated at low temperatures. The low frequency inductive method was used to detect a superconducting transition. All the samples were studied by X-ray diffraction (XRD), solid state nuclear magnetic resonance (NMR), electron spin resonance (ESR), and Raman scattering. It is found that most of the superconducting heterofullerides are potassium heterofullerides. For the fulleride K2GaHgxC60 the critical temperature of the superconducting transition is Tc = 20 K. Indium and boron heterofullerides are not superconductors. The synthesis of heterofullerides via amalgams (Hg–K–Mg, Hg–Rb–Al) gives rise to two different superconducting phases.

Superconductivity of Fullerides with Composition AGa $$_{x}$$ x C $$_{60}$$ 60 and AGa $$_{x}$$ x M $$_{y}$$ y C $$_{60}$$ 60 (A = K, Rb; M = In, Sn, Bi)

“…The estimation shows that 70 % of the sample volume is in a superconducting state at temperature 4.2 K. We also synthesized from gallams the superconducting fullerides with composition KGa x Sn y C 60 and KGa x Bi y C 60 with T c equals to 17 and 10 K correspondingly. The only known superconducting heterofulleride with one atom of potassium (and not containing other alkali metals) was the fulleride with composition KMg 2 C 60 [5]. Thus, the synthesis from liquid gallium or gallams allowed increasing essentially the range of composition for superconducting fullerides with only one atom of potassium.…”

“…2a been studied by EPR in Refs. [5,20]. These paramagnetic centers are most likely the negatively charged oxygen complexes (e.g., C 120 O or C 60 O) or dimers (C 120 ) [21,22].…”

“…The only known superconducting fullerides with one atom of alkali metal now are the fullerides with composition KMg 2 C 60 with T c = 16 K and RbBe 2 C 60 with T c = 13 K [5]. The first one was obtained by the exchange reaction of K 5 C 60 with two equivalents of MgCl 2 in the environment of tetrahydrofuran, and the second was obtained by exchange reaction of Rb 5 C 60 with two equivalents of BeCl 2 .…”

“…Later on, the superconductivity was also found in fullerides with two atoms of the alkali metal and one atom of a heterometal. These compounds were obtained either by the exchange reactions of A n C 60 (A-K, Rb; n = 3-5) with halogenides of metals of 2, 3, 8-13 groups [5,6] or by the interaction with alloys of metals with mercury [7,8]. It was shown that fullerides with two atoms of alkali metal and gallams are superconductors [9,10].…”

“…transitions of fullerides were defined by low-frequency induction method by measuring the temperature dependence of the magnetic susceptibility in the temperature range of 4.2-100 K [5,6].…”