Theory of the reciprocal susceptibility of the trigonal boracites and the experiment scheme

Landau theory is used to describe the ferroelectric trigonal phase of Boracites. The temperature dependence of the principal reciprocal susceptibility is obtained. The calculated result shows that at the Curie temperature Tc, the spontaneous polarization jumps. The component of the principal reciprocal susceptibility perpendicular to polarization jumps but the component parallel to polarization does not. A possible experimental scheme for the measurement of the principal reciprocal susceptibility components is presented.