Preparation and properties of ferroelastic/ferroelectric polytypes of antimony(III) oxide iodine,Sb5O7I |
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Authors: | R Nitsche V Krämer M Schuhmacher A Bussmann |
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Institution: | Kristallographisches Institut der Universität, Hebelstrasse 25, D-7800 Freiburg i. Br.,, West-Germany |
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Abstract: | Antimony oxide iodide, Sb5O7I (?7Sb2O3.SbI3), is monoclinic and exists in at least 8 polytypic modifications. Crystals of these (transparent, pseudohexagonal prisms up to 15 × 10 × 5 mm3) were grown by vacuum sublimation and identified by optical and X-ray methods. Depending on the stacking sequence of characteristic slabs of antimony and oxygen in the (monoclinic) b-direction, centric and acentric polytypes result. The former show pure ferroelastic, the latter combined ferroelastic + ferroelectric behaviour. All polytypes transform reversibly into hexagonal, nonferroic phases at characteristic Curie temperatures between 165 and 208°C. The crystals can assume one of the three stable orientation states which may be mutually switched into each other by successive application of comprehensive stress (of the order of 106 N/m2) on the three pairs of prism faces. In the ferroelectric polytypes the spontaneous polarization (about 5 × 10-3 C/m2) is not reversible but only reorientable by ± 120° by coercive fields in the order of 2–5 kV/cm. Ferroelectricity and ferroelasticity are fully coupled. |
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