Systematic variation of ferroelectric transition temperature within related isomorphic series

Many of the isomorphic series of ferroelectrics contain members with sequences of related atoms such as the alkali metals, the first transition group, the rare earths, the halides and also the isotopes hydrogen and deuterium. Tabulations are given of the manner in which T c varies with the H, D and elemental substitutions. In most cases, the changes occur in a systematic manner relative to the positions of the atoms in the periodic table, although this is not always the case. The ferroelectric members of the potassium dihydrogen phosphate or KDP class of compounds exhibit particularly striking regularities in their dependence of T c on elemental replacement, and these changes in T c have the following average values