Structure of Cleavage Surface of Ferroelectric TGS

Abstract

The macroscopic cleavage plane of TGS at the ferroelectric phase is slightly inclined to the b-plane when the cleavage propagating direction is roughly along the c-axis. The sense of the inclination is reversed with the direction of the cleavage propagation and with the polarity of domain. The microscopic structure of the cleavage surface was examined by electron microscopy utilizing the low angle shadow decoration technique. This technique revealed the detail of the surface on the crystallographic unit cell scale. The macroscopic inclination results from the formation of elementary steps of b₀ in height, where b₀ is the unit cell length along the b-axis. The cleavage steps are bent at domain boundaries to one particular side determined by the polarity of domain and the cleavage direction. The elementary step formation and the step bending at domain boundaries are interpreted by assuming that the bonding on the positive side of the cleavage crack front is more easily broken than that on the negative side. There is one particular cleavage direction in which steps of b₀/2 in height are formed. The surface discontinuity of b₀/4 or less were observed at domain boundaries. Such a characteristic surface structures are discussed in relation to the crystal symmetry of TGS. The cleavage plane in the unit cell is the positive side of the layer composed from SO₄ and glycine I at y=1/4 or 3/4.