Complex phosphates with the NASICON structure (M x A2(PO4)3)

Data on the synthesis and properties of NASICON complex phosphates M _x A₂(PO₄)₃ are summarized. The crystal chemistry and homology of these compounds are surveyed. The existence of large channels and numerous voids in the structure and various occupations of these voids by mobile cations generate many valuable physical and chemical properties of the M _x A₂(PO₄)₃ complex phosphates. The details of phase transitions, ionic conductivity, thermal expansion, ion-exchange properties, and sensor properties of the NASICON materials are considered, as well as the possibility of purposefully changing these properties through partial heterovalent substitution for the metal or phosphorus atoms.