Europhys. Lett.
Volume 64, Number 3, November 2003
Page(s) 351 - 357
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 November 2003
DOI: 10.1209/epl/i2003-00190-3
Europhys. Lett., 64 (3) , pp. 351-357 (2003)

Driving force for the proper ferroelastic phase transitions induced by cation exchange

N. N. Ovsyuk and S. V. Goryainov

Institute of Mineralogy and Petrology, Russian Academy of Sciences Novosibirsk, 630090, Russia

(Received 3 June 2003; accepted in final form 20 August 2003)

It is shown that the internal pressure may be represented as the driving force for the proper ferroelastic phase transitions induced by cation exchange. It has been found that the internal stress tensor, generated by the cation exchange, is of a more complicated nature than the tensor of the external stress. This difference comes from a specific coupling of the substituting cations with local, microscopic displacements of the neighbouring atoms inside the unit cell. It becomes evident why in a number of experiments a significant difference in the action of internal and external pressures on the crystal structure is observed and, also, why the internal pressure causes a greater anisotropy than the external one. An equation has been obtained, with the help of which it appears possible to predict the internal pressure of the proper monoclinic-triclinic ferroelastic phase transition induced by cation exchange if the initial effective elastic moduli are known.

62.20.Dc - Elasticity, elastic constants.
64.60.-i - General studies of phase transitions.

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