Electron Diffraction Study of an Inorganic Spin-Peierls System CuGeO₃

Abstract

An electron diffraction study of an inorganic spin-Peierls system CuGeO 3 was performed. Weak superlattice reflections indexed by ( h /2) k ( l /2)( h , k , l : o d d ) are observed in electron diffraction patterns taken at about 10 K with the [100] electron incidence. The reflections are interpreted as characteristic of a superlattice structure of the space group B b c m or B b m m with cell dimensions a '≃2 a , b '≃ b and c '≃2 c and with dimerization of Cu atoms along the quasi-one-dimensional [001] or the [010] direction, which is strong evidence of the spin-Peierls transition. Strong diffuse streaks which run along the c * -direction through the fundamental reflections are observed at the same temperature. The streaks are attributed to low-frequency transverse acoustic waves of the oxygen octahedra and can be precursors to another phase transformation below the spin-Peierls transition.