Numerical Determination of the Local Ordering of PbMg1/3Nb2/3O3 (PMN) from High Resolution Electron Microscopy Images
✍ Scribed by C. Boulesteix; F. Varnier; A. Llebaria; E. Husson
- Publisher
- Elsevier Science
- Year
- 1994
- Tongue
- English
- Weight
- 913 KB
- Volume
- 108
- Category
- Article
- ISSN
- 0022-4596
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✦ Synopsis
High Resolution Electron Microscopy (HREM) images of PMN (\left(\mathrm{PbMg}{1 / 3} \mathrm{Nb}{2 / 3} \mathrm{O}{3}\right)) taken along a (\langle 110\rangle) axis of the cubic (perovskite) structure show that ordered regions of the ({111}) type exist which correspond to (A B{1 / 2}^{\prime} B_{1 / 2}^{\prime \prime} \mathrm{O}{3}) composition. Wavy fringes in the ({111}) plane directions reveal some imperfect ordering. A numerical treatment of the HREM images was performed in order to determine both position and size of perfectly ordered regions. After a test experiment, this method shows that (i) ordered regions consist of clusters about (2 \mathrm{~nm}) in diameter regularly spread inside the crystal, (ii) the distance between the centers of neighboring clusters is about (2.5 \mathrm{~nm}). The regular arrangement of these clusters is due to their composition which differs from the mean composition. The composition of disordered regions is close to (\mathrm{PbMg}{1 / 4} \mathrm{Nb}{3 / 4} \mathrm{O}{3}). In this model some local electrical charge equilibrium could be obtained, at least partly, by oxygen and metal-atom vacancies. 1994 Academic Press, Inc.