CONICET | Buscador de Institutos y Recursos Humanos

&lt;!-- @page { margin: 2cm } P { margin-bottom: 0.21cm; direction: ltr; color: #000000; line-height: 115%; widows: 2; orphans: 2 } P.western { font-family: "Calibri", sans-serif; font-size: 11pt; so-language: pl-PL } P.cjk { font-family: "Times New Roman", serif; font-size: 11pt } P.ctl { font-family: "Calibri", sans-serif; font-size: 11pt; so-language: ar-SA } A:link { color: #0000ff } --&gt; We have constructed a simple lattice model for H-bonded ferroelectric crystals. The model accounts for the ice rules with a parameter k that sets a high energy cost fo the forbbiden protonic configurations. It also includes the dipole-dipole interaction along a preferred direction of a cubic lattice. By adjusting conveniently the parameters of the model, it could be applied to different H-bonded ferroelectric or antiferroelectric compounds as well as to ice. By means of Monte Carlo simulations with the replica exchange method, we study within this model the possibility of ferroelectric transitions in ice. We observe a ferroelectric transition with a Tc asymptotically independent of k for large values of this parameter. Thus, the transition to the ferroelectric state is achieved in the absence of protonic defects which violate the ice rules. Associating an arrow with the vector joining a proton with the nearest oxygen in the H-bond, we find closed rings of protons formed by chains of arrows. The state of highest probability in the disordered phase at high temperature is formed by closed rings of size 6, which provides a measure of the energy cost of the basic excitations. This kind of ring structure agrees with results in disordered cubic ice in recent neutron scattering experiments. On the other hand, we find that the size of the closed rings diverges in the vicinity of the ferro-para phase transition.