Ferroelectricity and Polarization-Wave Condensation in Twofold Incommensurate Phases

Certain different types of twofold incommensurate phases are possible (an account of which was given recently). Their meanings are set forth again. It is manifested that some of them are ferroelectric or, in other words, a homogeneous or nonwavy polarization component is condensed in some of them. The direction of ferroelectricity is the same as in the corresponding commensurate ferroic phase. The faintness index of ferroelectric transition differs with different types of incommensurate phases (including the semicommensurate type). Nonferroelectric types of incommensurate phases (including the onefold incommensurate type) can be dielectrically distinguished from each other by taking polarization-wave condensation into consideration.