A MODEL FOR THE DIELECTRIC BEHAVIOR OF [N(CH3)4]2XCL4 WITH X=CO, ZN

A phenomenological model for the dielectric anomaly at the incommensurate-ferroelecmc phase transition in [N(CH3)4]2XC14 (X=Co,Zn) is presented. A first order transition between the incommensurate phase (in a sinusoidal regime) and the ferroelecmc phase is assumed. A divergency of the dielectric susceptibility of the incommensurate phase when the modulation wave vector passes through the commensurate 2/5 value is predicted. Its functional form differs from the usual Curie-Weiss law. The experimental dielecmc behaviour can be reproduced if the coexistence of both phases, as determined from x-ray measurements, is taken into account. © 1990, Taylor & Francis Group, LLC. All rights reserved.