Equilibrium morphologies and thermal roughening of cesium halides

Equilibrium morphologies of three types of cesium halide crystals in saturated aqueous solution droplets are observed for temperatures ranging from 275 to 344 K. For all temperatures, cesium iodide crystallites are bounded by planar {110} facets, which indicates that these faces are below the roughening temperature. On the other hand, cesium chloride surfaces are thermally roughened in this temperature regime, as follows from their rounded morphology. For cesium bromide a roughening transition is observed at a temperature of 278+/-1 K This value of the roughening temperature allows us to estimate the effective bond energy at the surface of this ionic compound. The abruptness of the transition, which takes place within 2 K, suggests that probably it is not of the Kosterlitz-Thouless type. (C) 2002 Elsevier Science B.V. All rights reserved.