Sound Velocity Measurements in Highly Oriented and Intercalated Graphite Specimen by Direct Electromagnetic Excitation of Ultrasound

Abstract

Actually Graphite Intercalation Compounds (GIC) are of increasing practical and fundamental interest because of their highly anisotropic structure and high in-plane conductivity. Along the c axis they show a well-defined periodic sequence of graphite layers and ordered (or disordered) intercalant layers. Compared to the strongly coplanar bonded graphite layers, the interlayer interactions are relatively weak, thereby giving rise to highly anisotropic physical properties. In spite of numerous investigations, however, the origin of the long-range forces involved in the formation of the interplane intercalation structure, as well as the quasi 2D commensurate-to-glass phase transition /1/,/2/, are still not well understood. Ultrasonic measurements therefore are of particular interest since they provide direct information about the interaction forces among the intercalant and graphite layers. Moreover, the sound velocity is highly sensitive to cooperative phenomena and therefore to thermodynamical structural fluctuations appearing in the vicinity of a phase transition point.