Phosphates and phosphonates of tetravalent metals as protonic conductors

16 Phosphates and phosphonates of tetravalent metals as protonic conductors 

After 1964, the discovery that layered crystalline compounds (general formula M(IV)(HO—P03)2. HjO) can be obtained by refluxing amorphous materials or prepared directly by slow precipitation in the presence of HF gave rise to an increased interest in these inorganic ion-exchangers. 

In recent years, these compounds have begun to find practical applications not only as ion-exchangers but also as intercalating agents, molecular sieves, catalysts and ionic conductors. The reader interested in synthetic and structural details and/or general aspects and applications of these materials is referred to books and recent reviews . 

In this chapter, our attention is focused on proton transport in a-zirconium phosphate and its derivative phases which are presently the most investigated materials, while only a brief account of proton transport in other materials of this class is given. Further details on the conductivity of other acid salts of tetravalent metals can be found in the literature . The relation between thermal behaviour, IR spectroscopic properties and a possible conduction mechanism in a-zirconium phosphate has recently been discussed by Colomban (see pp. 280-1). 

---