Tb2(Mo O4)3 spontaneous shear strain measurements and free energy expression

Abstract
The spontaneous shear strain uxy versus the temperature is measured by the y ray diffractometry technique in the (300 K-430 K) range. The first-order type of the ferroelectric-ferroelastic transition is clearly demonstrated (discontinuity of some 100" for uxy at the transition temperature Ttr) : our data are in accordance with phenomenological descriptions corresponding to the free energy expressions with four adjustable parameters