Microscopic free energy and order parameters of antiferroelectrics

A microscopic free energy function for antiferroelectrics has been derived as a power series in a complete set of order parameters which are the thermal averages of normal coordinates whose wave vectors form a group G. Furthermore it has been shown that the wave vectors of the non-zero order parameters at all the extrema of the free energy form subgroups of G and that there will always be a net polarization in the antiferroelectric phase. The general discussion is illustrated by application to the antiferroelectric transition of PbZrO3. © 1967.