Synthetic Metals, 12 (1985) 27-32 27 ORDERING AND KINETICS IN GRAPHITE INTERCALATED WITH NITRIC ACID ROY CLARKE, PEDROHERNANDEZ, HITOSHI HOMMA*and ELLEN MONTAGUE ¢ Physics Department, The University of Michigan, Ann Arbor, MI 48109 (U.S,A.) ABSTRACT Molecular ordering in HNO3-graphite is studied by X-ray scattering. Two stable in-plane configurations coexist at T~250K and both appear to be registered with graphite. One configuration is hexagonal and the other oblique, the latter possibly stabilized by a ~12° tilt of the nitrate group. Time resolved X-ray scattering shows that the evolution of the oblique phase is very sluggish. INTRODUCTION While nitric acid graphite was the first intercalation compound to be synthesized, more than 150 years ago, its structure is still not well understood [1]. Here, we report on an X-ray study of HNO3-graphite with the aim of probing the temperature dependence of the molecular arrangement, especially the in-plane structure. The structure of many molecular graphite intercalation compounds (GICs) can be described in terms of long-period superlattices, either commensurate or incommensurate with the graphite host [2,3]. Our major interest in HNO3-GIC is the possibility that the intercalant could break the symmetry of the host graphite to produce a non-hexagonal structure which may be quasi-two- dimensional at the higher stages. In particular the behavior can be con- trasted with that of the more isotropic, hexagonal, structures; for example, SbCI5-GIC which shows interesting kinetic phenomena associated with the ordering of the J-7 x~'7 in-plane superlattice [3]. *Present address: Argonne National Laboratory, Argonne, IL 60439, U.S.A. tPresent address: Energy Conversion Devices, Troy, MI 48084, u.s.A. 0379-6779/85/$3.30 © Elsevier Sequoia/Printed in The Netherlands