The way in which nonstoichiometry and order and disorder interrelate in solid phase compounds is discussed. Nonstoichiometry due to the presence of structural vacancies is widely found in such solid phase compounds as transition metal carbides, nitrides and oxides, and in related ternary interstitial compounds. It is shown that it is nonstoichiometry that determines the disordered or ordered distribution of atoms and vacancies. A review is given of the current status of research into disorder—order phase transitions in strongly nonstoichiometric cubic and hexagonal compounds. Symmetry analysis results for disorder—order and order—order phase transformations are considered in detail. Key superstructure types that form in nonstoichiometic compounds with vacancies in one or two sublattices are described.

PACS: 61.43.−j, 61.50.Ah, 61.50.Ks, 61.66.Fn, 61.72.jd, 61.72.jj (all) DOI: 10.3367/UFNe.0184.201409a.0905 URL: https://ufn.ru/en/articles/2014/9/a/ 000346959600001 2-s2.0-84933499554 2014PhyU...57..839G Citation: Gusev A I "Nonstoichiometry and superstructures" Phys. Usp. 57 839–876 (2014) BibTexBibNote ® (generic)BibNote ® (RIS)MedlineRefWorks Received: 24th, October 2013, revised: 26th, November 2013, accepted: 27th, November 2013 Оригинал: Гусев А И «Нестехиометрия и сверхструктуры» УФН 184 905–945 (2014); DOI: 10.3367/UFNr.0184.201409a.0905