Order-disorder transition and stability of ordered state

A review of experimental data on order-disorder phase transitions is given. Information on the type and temperature of the transformation and the temperature dependence of the long-range-order parameter is systematized. The conditions of stability of structures with long- and short-range order are analyzed using a pair-interaction model. The relation between the form of the Fermi surface and the structure of the ordered state is shown.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 82–92, August, 1976.In conclusion, the author thanks N. N. Golobokov, V. M. Dement'ev, N. M. Kormin, V. M. Kushnarenko, S. V. Starenchenko, A. S. Tailashev, and D. M. Shtern f o r fruitful collaboration in the writing of the present work.