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Polytypism in MX 2 Compounds: A Case of Mixed Equilibrium Phases
Author(s) -
Ahmad Shandar,
Wahab M. A.
Publication year - 1993
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170280310
Subject(s) - stacking , hamiltonian (control theory) , thermodynamics , crystallography , materials science , chemistry , physics , mathematics , mathematical optimization , nuclear magnetic resonance
Classical polytypism in MX 2 ‐type compounds has been investigated. It has been established that polytypism can be understood, not as the case of independent stacking of A, B, or C layers but in terms of basic structural units, the most stable and only equilibrium phases of the given compounds. Other polytypes are formed only as a result of various equivalent positions that these units can take a given cell height. A criterion to predict whether a given compound would exhibit polytypism is also suggested. Several problems in applying ANNNI and other spin models to polytypism have been pointed out and a modified Hamiltonian is suggested.