Nomenclature of magnetic, incommensurate, composition- changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr working group on Phase Transition Nomenclature Citation for published version (APA): Toledano, J. C., Berry, R. S., Brown, P. J., Glazer, A. M., Metselaar, R., Pandey, D., Perez-Mato, J. M., Roth, R. S., & Abrahams, S. C. (2001). Nomenclature of magnetic, incommensurate, composition-changed morphotropic, polytype, transient-structural and quasicrystalline phases undergoing phase transitions. II. Report of an IUCr working group on Phase Transition Nomenclature. Acta Crystallographica. Section A, Foundations of Crystallography, A57, 614-626. https://doi.org/10.1107/S0108767301006821 DOI: 10.1107/S0108767301006821 Document status and date: Published: 01/01/2001 Document Version: Publisher’s PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication: • A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website. • The final author version and the galley proof are versions of the publication after peer review. • The final published version features the final layout of the paper including the volume, issue and page numbers. 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Abrahamsi*} Applied Physics. § Ex officio, International Union of Pure and Applied Chemistry. aLaboratoire des Solides IrradieÂs and Department of Physics, Ecole Polytechnique, F-91128 } Ex officio, IUCr Commission on Crystallo- Palaiseau CEDEX, France, bDepartment of Chemistry, University of Chicago, 5735 South Ellis graphic Nomenclature. Avenue, Chicago, IL 60637, USA, cInstitut Laue±Langevin, BP 156X CEDEX, F-38042 Grenoble, France, dClarendon Laboratory, University of Oxford, Parks Road, Oxford OXI 3PU, England, eLaboratory for Solid State and Materials Chemistry, Eindhoven University of Technology, PO Box 513, NL-5600 MB Eindhoven, The Netherlands, fSchool of Materials Science and Technology, Banaras Hindu University, Varanasi 221005, India, gDepartamento de FõÂsica de la Materia Condensada, Universidad del PaõÂs Vasco, Apdo 644, E-48080 Bilbao, Spain, hB214, Materials Building, National Institute of Standards and Technology, Washington, DC 20234, USA, and iPhysics Department, Southern Oregon University, Ashland, OR 97520, USA. Correspondence e- mail: [email protected] A general nomenclature applicable to the phases that form in any sequence of transitions in the solid state has been recommended by an IUCr Working Group [Acta Cryst. (1998). A54, 1028±1033]. The six-®eld notation of the ®rst Report, hereafter I, was applied to the case of structural phase transitions, i.e. to transformations resulting from temperature and/or pressure changes between two crystalline (strictly periodic) phases involving modi®cations to the atomic arrangement. Extensive examples that illustrate the recommendations were provided. This second Report considers, within the framework of a similar six- ®eld notation, the more complex nomenclature of transitions involving magnetic phases, incommensurate phases and transitions that occur as a function of composition change. Extension of the nomenclature to the case of phases with less clearly established relevance to standard schemes of transition in equilibrium systems, namely polytype phases, radiation-induced and other transient phases, quasicrystalline phases and their transitions is recommended more tentatively. A uniform notation for the translational periodicity, propagation vector or wavevector for magnetic and/or incommensurate substances is speci®ed. The notation adopted for incommensurate phases, relying partly on the existence of an average structure, is also consistent with that for commensurate phases in a sequence. The sixth ®eld of the nomenclature # 2001 International Union of Crystallography is used to emphasize the special features of polytypes and transient phases. As in Printed in Great Britain ± all rights reserved I, illustrative examples are provided for each category of phase sequence. 1. Introduction function of temperature and/or pressure may be found in the A multiplicity of terminologies for distinguishing individual crystallographic and other literature of the condensed state. members of a sequence of crystalline phases that form as a Confusion caused by the lack of a uni®ed nomenclature led the Commission on Crystallographic Nomenclature to estab- 2 1 Established 15 February 1994 by the IUCr Commission on Crystallographic lish a Working Group on Phase Transition Nomenclature. Nomenclature; following the resignation of two members upon acceptance of The Working Group was charged with studying the multiple the ®rst Report, three new members were appointed 18 July 1998. This second nomenclature in current use for naming such sequences of Report was received by the Commission 26 February 2001 and accepted 19 April 2001. The present Report, as all other Reports of the Commission, is phases and with making such recommendations for its available online at the Commission's webpage: http://www.iucr.org/iucr-top/ comm/cnom.html. 2 See footnote to paper title. 614 ToleÂdano et al. Phase-transition nomenclature Acta Cryst. (2001). A57, 614±626 research papers improvement as may be appropriate. The term `phase-transi- Table 1 tion nomenclature', as used throughout this Report, applies to Recommended abbreviations for various magnetic categories. the nomenclature of phases that form as a consequence of one Property Abbreviation Property Abbreviation or more transitions; the nomenclature of materials that exist Paramagnet P Exotic EX only in single phase form is adequately treated elsewhere, e.g. Ferromagnet F Amplitude modulated IC Leigh et al. (1998). Antiferromagnet AF Helical H In I, the general purpose of the nomenclature was de®ned, Spin ¯op SF Canted ferromagnet CF Weak ferromagnet WFM the relevant information it should contain was speci®ed, and a recommendation was made for the adoption of a six-®eld notation in the case of structural phase-transition nomen- clature, i.e. of transitions between two crystalline (strictly periodic) phases that involve only a modi®cation of the atomic arrangement. Extensive examples providing illustrative use of the nomenclature were presented for a variety of substances unambiguously indicated by the number Z of structural units (metals, alloys, oxides and minerals) that undergo phase in the conventional cell. transitions as a function of temperature and/or pressure. The A recommended adaptation of the six-®eld nomenclature to recommended notation is not only unambiguous; it also magnetic phase transitions is now presented. provides a full context for the transitions undergone by each phase. 2.1. First field The recommended nomenclature employs the following six- The usual name used in the literature for a magnetic phase ®eld notation for each phase with given chemical composition, tends to emphasize the magnetic behaviour of the phase. For each ®eld being separated from the others by vertical bars: instance, antiferromagnetic phases are often nicknamed AF1, Usual Temp: K Space-group Number of Ferroic Comments AF2 etc; likewise, spin ¯op phases are nicknamed SF1, SF2 etc. label in and symbol and chemical properties In simple situations where either temperature or magnetic literature pressure number formulas ®eld is the dominant parameter controlling the phase diagram, ; I; ... range Pa per unit cell the numeral in the nickname commonly increases with decreasing temperature (e.g. in antiferromagnetic phases), or Full information concerning the content of each ®eld is commonly