On the nature of different temperature dependences of the size of antiphase domains in commensurate long-period structures

First-principle calculations of the electronic structure and electronic susceptibility were performed to study the relation between the nesting properties of the Fermi surface and the character of the temperature dependence of long-period structures of two types exemplified by Ag₃Mg and Al₃Ti alloys. The observed temperature dependence of the long period length 2M in the Al₃Ti alloy was analyzed. It was shown that the temperature dependence of the size of the antiphase domain in long-period commensurate structures was determined by the special features of the electronic structure of the system, in particular, by the geometry of Fermi surface nesting regions.