Ferroelectric and Ferroelastic Phase Transitions in Molybdates and Tungstates of Monovalent and Bivalent Elements

Ferroelectric and ferroelastic phase transitions in molybdates and tungstates of monovalent and bivalent elements are reviewed. The nature and peculiarities of these transitions are briefly discussed. Most of interesting phase transitions are observed in compounds, containing monovalent ions, while among compounds of bivalent elements, only perovakites have properties of interest. Some molybdates and tungstates under consideration are improper ferroelectrics and ferroelastics, some of them have non-reversible, but reorienting, spontaneous polarization, some have modulated phases. There are indications on possibility of the ferroelectric state formation as a result of a reconstructive phase transition. Some crystal chemical problems are briefly discussed.

Keywords:

• Ferroelectric
• ferroelastic
• molybdates
• tungstates