Microscopic mechanism

of the cubic-rhombohedral phase transition in LiNbO3

 

A. Toumanari1, M. Bour2*, E. El-lfrikhe1, D. Khatib1

1 Laboratoire de Physique du Solide Théorique, F.Sciences, B.P. 8106, Université Ibn Zohr, 80000, Agadir,  Maroc

2 Laboratoire Matériaux, Systèmes et Technologie de l’Informations, Université Ibn Zohr, ESTA BP 33/S, 80000 Agadir, Maroc

* Corresponding author. E-mail: bour@esta.ac.ma

Received: 25 November 2006; revised version accepted:17 July 2007

 

Abstract

     The cubic-rhombohedral phase transition in LiNbO3 is discussed quantitatively from the microscopic free energy based upon the mean field approximation. Through the comparison between KNbO3 and LiNbO3 it is possible to understand that the electronic polarizabilities of the A ions (A = K or Li) plays an important role for the mechanism of the successive phase transition in these materials. From the calculation of the microscopic free energy, it is shown that the transition temperature and the order of the phase transition are well explained by this model.

 

Keywords: LiNbO3; First (second ) order phase transition ; Order phase transition; Mean field approximation; Electronic polarizability; Displacive-type; Spontaneous deformation; Local field.

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