The ferroelectric phase transition in tridymite type BaAL2O4 studied by electron microscopy |
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| Authors: | A M Abakumov O I Lebedev L Nistor G Van Tendeloo S Amelinckx |
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| Institution: | 1. Department of Chemistry , Moscow State University , Moscow, Russia , 119899;2. EMAT, University of Antwerp (RUCA) , Groenenborgerlaan 171, Antwerp, Belgium , B-2020;3. EMAT, University of Antwerp (RUCA) , Groenenborgerlaan 171, Antwerp, Belgium , B-2020;4. Institute of Crystallography , RAS, Leninsky prospekt 59, Moscow, Russia , 117333;5. National Institute of Materials Physics , P.O. Box. MG-7, Magurele, Bucharest, Romania;6. Phone: +32–3–2180262 Fax: +32–3–2180262 E-mail: gvt@ruca.ua.ac.be |
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| Abstract: | The paraelectric-ferroelectric (PE-FE) phase transition in stuffed tridymite BaAl2O4 was studied in situ by transmission electron microscopy. Electron diffraction revealed that the PE and FE phases have hexagonal symmetry. The PE-FE phase transition is accompanied by a doubling of the cell dimensions in the a-b plane. The transition is reversible, takes place over a wide temperature range (400–670 K.) and the interfaces related to the transition have a fluctuating character. The crystal structure of the high temperature PE phase was determined by high resolution electron microscopy. The structures of the PE phase (space group P6322, a≈ 5.22 Å, c ≈ 8.8 Å) and of the FE phase (space group P63, a= 10.4469(1)Å, c = 8.7927(1)Å) differ mainly by the configuration of the Al-O strings oriented along the c-axis. In the PE phase all the strings are equivalent whereas straight and corrugated strings alternate in an ordered manner in the FE phase resulting in doubling of the a and b cell parameters. Translation and orientation domains due to the decrease of the translation and point symmetry were frequently observed. |
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| Keywords: | Barium aluminate Electron microscopy Phase transition Ferroelectrics |
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