D 2h D 3d /D 5d T < 400 K T > 400K hindered rotation quasi-isotropic rotation

1. Temperature dependence of K4C60 Temperature dependence of Rb4C60 Temperature dependence of Cs4C60 Introduction K4C60, Rb4C60, Cs4C60 Na4C60 96 K 110 K 87 K Mott-Jahn-Teller insulator [1] Cs4C60 300 K JTE: pn h  Ih D5d / D3d/D2h[2] K4C60 Rb4C60 300 K 300 K 475 K [5] Detected molecular distortions: Cs4C60 neutron diffraction: D2h at 5 K, 293 K [3] K4C60 IR: D2h at 20-200 K, D3d / D5d at 300 K[4] Ci Transition temperature: 260-280 K Transition temperature: 200-220 K Transition temperature: 270-290 K, 400 K Preparation 4 Na + C60 4 K + C60 4 Rb + C60 4 Cs + C60 Na4C60 K4C60 Rb4C60 Cs4C60 350 oC 20 d 350 oC 10 d 200 oC 10 d 350 oC 10 d Correlation table Measurements 1 regrind 1 regrind 1 regrind 1 regrind A4C60 (A = Na, K, Rb, Cs) are air sensitive  preparation and KBr pellet pressing in dry box measurements in dynamic vacuum Sample characterization: XRD, Raman, IR  purity > 95 % IR measurements: LN2 cooled cryostat Bruker IFS28 FT-IR transmittance measurements while warming up Linewidth (cm-1) Comparison at room temperature Na4C60 Ci 4Au + 4Au + 4Au every T1u split many strong new modes  covalent bonding + 800 cm-1 mode (typical strong distortion of single bonded fullerene polymers) Cs4C60 D2h 4B1u + 4B2u + 4B3u Rb4C60 D3d / D5d 4Eu + 4A2uonly T1u(3) & (4) splitting observed few, weak new modes  weak distortion K4C60 D3d / D5d 4Eu + 4A2u C60 Ih 4T1u Conclusion IR Absorbance (a.u., baseline corrected) Staggered static distortion References [1] M. Fabrizio and E. Tosatti, Phys. Rev. B 55, 13465 (1997). [2] C. C. Chancey and M. C. M. O’Brien, The Jahn-Teller effect in C60 and Other Icosahedral Complexes (Princeton University Press, Princeton, 1997). [3] P. Dahlke and M. J. Rosseinsky, J. Mater. Chem. 14, 1285 (2002). [4] K. Kamarás, G. Klupp, D. B. Tanner, A. F. Hebard, N. M. Nemes and J. E. Fischer, Phys. Rev. B 65, 052103 (2002). [5] G. Oszlányi, G. Baumgartner, G. Faigel and L. Forró, Phys. Rev. Lett. 78, 4438 (1997). [6] V. Brouet, H. Alloul, S. Garaj and L. Forró, Phys. Rev. B 66, 155122 (2002). [7] R. M. Fleming, M. J. Rosseinsky, A. P. Ramirez, D. W. Murphey, J. C. Tully, R. C. Haddon, T. Siegrist, R. Tycko, S.H. Glarum, P. Marsh, G. Dabbagh, S. M. Zahurak, A. V. Makhija and C. Hampton, Nature 352, 701 (1991). [8] C. Goze, F. Rachdi and M. Mehring, Phys. Rev. B 54, 5164 (1996). n* / cm-1 Distortions of C60 studied by infrared spectroscopyG. Klupp, F. Borondics, G. Oszlányi, K. Kamarás, N. M. Nemes*, J. E. Fischer*, A. F. Hebard**, D. B. Tanner**Research Institute for Solid State Physics and Optics,P. O. Box 49, Budapest, H 1525, Hungary, email: klupp@para.chem.elte.hu*Laboratory on the Research of the Stucture of Matter,University of Pennsylvania, Philadelphia, PA 19104, USA**Department of Physics, University of Florida, Gainesville, FL 32611, USA Funding: Hungary OTKA T 034198, T 029931 US NSF-INT 9902050 4- IR(this work) D2h D3d/D5d K4C60 T < 260-280K T > 260-280K Rb4C60 T < 180-220 K T > 180-220 K NMR [6,8] hindered rotation axial rotation K4C60 T < 250 K 250 K < T < 580 K XRD [7,3] bct ordered anions@bco molecular axis or nonparallel with c merohedral disorder@bct staggered static distortion static JTE or dynamic JTE potential field of molecular JTE counterions dominates dominates D2h D3d/D5d T < 400 K T > 400K hindered rotation quasi-isotropic rotation T < 350 K T > 350 K bco bct ordered anions molecular axis nonparallel with c staggered static distortion static JTE or dynamic JTE potential field of molecular JTE counterions dominates dominates