X-Ray Critical Scattering in Ferroelectric Tri-Glycine Sulphate

The x-ray critical scattering due to the polarization fluctuation in Tri-Glycine Sulphate in the vicinity of the ferroelectric Curie point ( T C =48°C) has been observed in order to clarify the nature of inter-dipolar interaction to cause its phase transition. The observed critical scattering intensity shows a strong anisotropy around the reciprocal lattice points, with very narrow width in the direction of the polar axis. Based on the Ising model, the result was analyzed and it was found that the observed anisotropy was due to the long range electrostatic interaction between constituent microscopic dipoles. The critical behavior of the inverse correlation range, expressed as κ= A ( T / T C -1) ν , is investigated. From the temperature dependence of the critical scattering, the following values are obtained in the a -direction: A =0.18 6 Å -1 , ν=0.50 2 . The value of the critical exponent ν is in good agreement with that obtained in the molecular field approximation.