Nanosegregation in Na 2 C 60 G. Klupp, P. Matus, D. Quintavalle*, L. F. Kiss, É. Kováts, N. M. Nemes +, K. Kamarás, S. Pekker, A. Jánossy* Research Institute for Solid State Physics and Optics, P. O. Box 49, H-1525 Budapest, Hungary, *Department of Experimental Physics, Budapest University of Technology and Economics, Budapest, Hungary + NIST Center for Neutron Research, Gaithersburg, MD, USA; Department of Materials Science & Engineering, University of Maryland, College Park, MD, USA Funding OTKA T , T , T Preparation 350 o C 23 d, 450 o C 7 d 4 regrinds 2 Na + C 60 Na 2 C 60 Sample preparation and measurements were done in inert atmosphere Motivation  Study of Mott – Jahn – Teller insulating state C C K 2 C 60, Rb 2 C 60, Cs 2 C 60 do not exist X-ray diffraction Single phase simple cubic Pa3 a = Å The same as in [1] Solubility C 60 could be extracted with toluene from Na 2 C 60 in 11 days Concentration of the obtained C 60 solution was measured with HPLC  26-33% of the sample is neutral C % C C-NMR Peak with fast T 1 : the same as in [4], due to the metallic phase Peak with slow T 1 : 25 ± 5 % C 60 [5] Infrared spectroscopy Room T: C 60 + C 60 [2], the latter in a metallic phase High T: C 60 distorted by molecular Jahn – Teller effect [3] Reversible change  C 60 present at room T is not from off-stoichiometry Retransformation is complete after ~2 weeks  slow Na + diffusion even at room T K A C 60, D 3d /D 5d 2- C References [1] T. Yildirim et. al., Phys Rev Lett. 71, 1383 (1993) [2] T. Pichler et. al., Phys. Rev. B 49, (1994) [3] K. Kamarás et. al., Phys. Rev. B 65, (2002) [4] V. Brouet et. al., Phys Rev B 66, (2002) [5] R. Tycko et. al., Phys. Rev. Lett. 67, 1886 (1991) [6] A. Meyer et. al., Rev. Sci. Instrum. 74, 2759 (2003) [7] T. Becker et. al., Phys. Rev E 67, (2003) [8] G. Faigel et. al., Phys. Rev. B 52, 3199 (1995) [9] R. W. Schurko et. al., J. Solid State Chem. 177, 2255 (2004) Conclusions ~3-10 nm : C 60 : Na Nanosegregation Room T: XRD: Na 2 C 60 IR, NMR, ESR, HPLC: ~ 70 % Na 3 C 60 + ~ 30 % C 60 Structure is similar to that of the intermediate phase of KC 60 [8] Main phases in Na 2 C 60 : insulating C 60 + metallic Na 3 C 60 Size range of structural coherence: upper limit: XRD, lower: metallicity: Segregation was also seen in nominally Na 3 C 60 samples [9] On heating: jump-diffusion of Na +, segregation disappears At high T: homogenous Na 2 C 60 C 60 is D 3d /D 5d distorted because of the molecular JTE 2- ESR Static  is the same as in [4] K: 4 phases: 3 metallic + 1 insulator Curie paramagnet: ~ 1 % C 60 embedded in C 60, separated from metallic phases  amount of C 60 is nonnegligible - insulatormetals ESR intensity was normalized to static  measured by SQUID Neutron scattering 400 K: Na + jump diffusion becomes faster than 1 ns The different T trans in IR is due to the different timescales Q = 1 Å -1  jump distance is 4.5 Å  jump between T and off-centered O site Measurements were done on the High Flux Backscattering Spectrometer of NIST [6,7] Na + has the same nearest neighbour distances