Antonio Romano

Structure of Weiss domains in ferroelectric crystals

Abstract The structure of Weiss domains in ferroelectric crystals in each of which the polarization vector is constant, is investigated through a new variational principle. The general field equations are obtained and it is shown that in the presence of external electric field the total electric field is also constant in Weiss domains but is usually different from that of the polarization field. Moreover, it is proved that domain walls can only be planar surfaces. Finally the case corresponding to pure polarization fields is also treated and an illustrative problem is considered.

Structure of weiss domains in elastic ferroelectric crystals

Abstract In this work a variational principle is proposed to study the existence and structure of Weiss domains in elastic ferroelectric crystals. Weiss domains are defined as certain subregions of the crystal in each of which the polarization vector is uniform and has a constant magnitude which is equal to the saturation polarization per unit mass for the crystal. The variational principle differs from previous ones in that the variations of the domain walls are also taken into account and it is a direct generalization of the one corresponding to the rigid crystals which we have proposed earlier. In deriving the general theory the dependence on the polarization gradients are also considered and the effect of this dependence when passing from one domain to another is represented by an appropriately chosen surface energy on domain walls. The domain structure is studied under homogeneous deformation. The effect of a small deformation field on the shape of domains is illustrated in the case of a rectangular uniaxial crystal which has initially no electric field inside. It is shown that the deformation creates a small electric field in the crystal and domain walls change slightly.

The Gibbs principle for the equilibrium of crystals

Abstract The equilibrium shapes of a crystal surrounded by its melt are analysed starting from a general Gibbs principle. The equilibrium system is derived assuming the presence of nonlocal interactions among the surface particles and those of the crystal and of the edges. Finally the equilibrium system is suitably simplified to derive Wulff s law.

Sulla termodinamica dei materiali di tipo differenziale in campi elettromagnetici

SuntoSi determinano le equazioni approssimate del bilancio relativistico di un sistema continuo carico ed, associando ad esse la versione relativistica della diseguaglianza di Clausius-Duhem proposta da P. M. Quan, si estendono i risultati della termodinamica di Coleman dei materiali differenziali al caso che sia presente un campo elettromagnetico.