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LOCAL VERSUS LONGRANGE STRUCTURE IN LEAD ZIRCONATETITANATE A.M. Glazer Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK AND Department of Physics, Warwick University, Coventry CV4 7AL, UK Lead zirconatetitanate ceramic (PZT) is the most commonly used piezoelectric material worldwide. Despite this, the origin of the high piezoactivity has been a matter of discussion for around 50 years. Although this problem has still not been solved fully, careful studies of the local and longrange crystal structures using both neutron and Xray diffraction has begun to reveal just how complex this material actually is. Work over the last few years is now giving more insight into the link between the properties of PZT and its atomic arrangements., Керамика цирконаттитанат свинца (PZT) является наиболее широко используемым пьезоэлектрическим материалом в мире. Несмотря на это высокие значения ее пьезосвойств обсуждаются уже около 50 лет. Хотя эта проблема до сих пор полностью не решена, тщательные исследования локальных и дальних кристаллических структур с использованием нейтронной и рентгеновской дифракции начали показывать, насколько сложен этот материал на самом деле. Работа, проведенная за последние несколько лет, теперь позволяет лучше понять связь между свойствами PZT и его атомным расположением.

Symmetry-element diagrams for the space group (17) for orthogonal projections along [001], [010], [100] (left to right).

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-field notation of the first 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 modifications to the atomic arrangement. Extensive examples that illustrate the recommendations were provided. This second Report considers, within the framework of a similar six-field 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 specified. 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 field of the nomenclature is used to emphasize the special features of polytypes and transient phases. As in I, illustrative examples are provided for each category of phase sequence.

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