Unusual Twinning in Graphite

Abstract

ACCORDING to the Kennedy interpretation¹ of twinning in graphite, the twin boundary can be regarded as the result of insertion or removal of a full hexagon width on alternate planes in the hexagonal lattice. This means that the twins are regions of the crystal which are misoriented in relation to the matrix by an angle of tilt, tan⁻¹ a/c, a and c being the unit cell dimensions, equal respectively to the width of a hexagon and the distance between alternate basal planes. This interpretation is corroborated by the recent work of Freise and Kelly², there being no doubt that the twin composition plane is {112caron;1} with respect to the morphological axes (conventional notation). In Kennedy's paper, theoretical reasons are adduced which favour the existence of {112caron;1} rather than {11caron;01} twins, which result from the insertion or removal of a hexagonal length, 2a/√3, into every other plane. It is also stated that “No cases of the observation of a {11caron;01} twin composition plane appear to have been reported, although it may be possible to produce such twins in thin flakes of very perfect graphite”. This statement forms the basis of this communication.