märkimisväärse morfoloogilise (struktuurse) erisusega faasipiir keraamilises materjalis; tuntud on piir romboeedrilise ja monokliinse ferroelektrilise faasi vahel piesoelektrokeraamilises materjalis (vt monotropism, piesoelektrokeraamika), a region in a phase diagram of a ceramic system where two crystalline polymorphs exist together in variable proportions with an intimate, mixed mictostructure; used to refer to the phase transition between tetragonal and rhombohedral ferroelectric phases as a result of varying the composition or as a result of mechanical pressure (see: monotrophism, piesoelectric ceramics)