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Phase Transitions in and Ferroelasticity of 9-Hydroxyphenalenone

Published online by Cambridge University Press:  21 February 2011

Christer Svensson  and
S. C. Abrahams
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Abstract

Crystalline 9-hydroxyphenalenone is monoclinic between 145 K and the melting point at 475 K. The space group is P21 below 255 K, P21/c between 255 K and 380 K, and I2/c above 385 K. A model for the 255 K transition involves inplane rotations of about 40° for one quarter of the molecules. Further rotation and translation takes place at the 380–385 K phase transitions. All three phases are expected to be ferroelastic, but at present only the unit cell of the room temperature phase has been reversibly reoriented. The spontaneous strain decreases from 0.24 at 145 K through 0.18 at room temperature to 0.14 at 430 K, assuming a tetragonal prototype. Domain walls are temperature dependent with orientation (1.86, 0, 1) and (1, 0, −1.86) at 298 K. Ferroelastic transformation proceeds by a slip process, approximately in the molecular planes. A prototype common to all three phases can be derived with space group P41. Macroscopically, the transformation is accompanied by a remarkable change of shape; if unfractured, the crystals exhibit shape memory.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 21: Symposium GREECE – Phase Transformations in Solids , 1983 , 149
Copyright
Copyright © Materials Research Society 1984

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References

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