Mechanisms of polytype stabilization during the wurtzite-sphalerite transition |
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| Authors: | M B Geilikman |
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| Institution: | 1. Institute of Experimental Mineralogy, USSR Academy of Sciences, 142432 Chernogolovka, Moscow district, USSR
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| Abstract: | Two mechanisms of solid-state formation of polytypes are suggested. The first is structural-kinetic by nature, the stabilization of short-period polytype (for example, 4H) being due to the fact that there are two possible structural types of nuclei in the wurtzite structure: when new phase growth takes place by means of two-dimensional nucleation, these short-period polytypes become kinetically stable although they do not correspond to the minimum of free energy, and appear as transitional phases. The second mechanism of polytype formation below the transition temperature is influenced by impurities which stabilize the hexagonal modification, in which case polytypes may arise as states that are stable with respect to a diffusionless structural wurtzite-sphalerite transformation and metastable relative to small fluctuations of impurity concentration. |
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