ON THE PREDICTION OF CRYSTAL MORPHOLOGY - I - THE HARTMAN-PERDOK THEORY REVISITED

The over 40 year old Hartman-Perdok (HP) [Hartman & Perdok (1955). Act a Cryst. 8, 49-52, 521-524, 525-529] theory for predicting crystal mor phology is reconsidered. The new approach, which gives a physical foun dation to the theory, is based on F faces having a roughening transiti on temperature higher than 0 K. The aim of this paper is to confront t he field of crystal growth and in particular the classical HP theory w ith modern statistical thermodynamical treatments of models of surface s of relatively simple crystal structures. It is shown that crystal fa ces (hkl) containing multiple connected nets with a relatively high en ergy content may have a very low roughening temperature and an unexpec tedly high growth rate. In some cases, crystal faces become rough at 0 K because of multiple connected nets related by symmetry giving rise to symmetry roughening. The use of connected nets in the HP theory off ers the possibility of extrapolating the results of statistical thermo dynamical models of simple crystal surfaces to more complex crystals a s encountered in practice. The role of the step free energy in underst anding crystal morphology is emphasized.