Some of studied crystals are characterized by unusual combination of ferroelectric and superionic properties. The most typical example are the KTiOPO4 - family crystals grown from fluxed melts and, especially, doped with some heterovalent elements such as Nb. This doping leads to formation of additional vacancies in the K sublattice and to enhanced mobility of alkaline cations. Conductivity of similar crystals can reach the value of order 5 · 10-2 Ohm-1cm-1 at 300oC what is close to conductivity of the best K-containing superionics.
Anomalous high ionic conductivity was noted also for the crystals AB2O6 with structure of "defect" pyrochlore type and some crystals AB3O9 of hexagonal tungsten bronze type. All these crystals have the wide channels in their structure in which situated movable alkaline cations. With the collective interaction of the latter the ferroelectric phase transitions seem to be associated. Further ferroelectrics - superionics are recently studied K3Nb3B2O12 crystals and their solid solutions.
Of special interest are Bi2WO6 and other related Bi-containing crystals with the layered crystal lattices. Their electric conductivity is attributed to unexpectedly high mobility of oxygen anions. In this connection it is interesting to note that the high-temperature superconductors with close related layered structures are also characterized by the presence of movable oxygen anions although their electronic conductivity prevails over ionic one.