Subkinds of the 22 Kinds of Ferroelectrics, Complexity in the Narrower Sense, and Ferro-Ferroelectric Phase Transformations

Abstract

Firstly, the concept of “subkinds” is defined, and the subkinds of each of the 22 ferroelectric kinds are determined. Secondly, on the basis of these results, the concept of complexity is refined; restrictions are imposed upon the extra symmetry elements in the definition of complexity. The new concept of complexity is narrower but more useful than the old one. It is expected that an arbitrary ferro-paraelectric phase transformation, if not primitive, is most probably complex in the narrower sense. (In fact, the ferro-paraelectric phase transformations known up to now are all primitive or ‘complex in the narrower sense.’) Thirdly, on the assumption of primitiveness and ‘complexity in the narrower sense.’ a determination is made of the possible point groups of the prototype common to two ferroelectric phases transforming to each other when their kinds are specified. It is found incidentally that a considerable number of pairs of kinds should be impossible for ferro-ferroelectric phase transformations. Lastly, comments are made on the concept of prototype and on the method of macroscopic free energy function.