Other phosphates and phosphonates of tetravalent metals

Tetravalent metals may also be bonded by XO4 and/or to R—XO3 groups so as to build up a layered structure different from the a-structure. These compounds are usually called y-layered M(IV) phosphates. Unfortunately, single crystals large enough for X-ray determination have not been obtained and the structure of y-compounds is still unknown. Recent 

While studying the Ce(IV)/phosphoric acid system, a fibrous material of composition Ce(HP04)2.2H2O was obtained . Similar results were obtained with thorium . The structure of these compounds is unknown. The fibrous materials are of interest for electrochemical devices because they can be used to obtain very thin, autoconsistent membranes. The conductivity of anhydrous and trihydrated cerium phosphate is reported in Table 16.2. The conductivity of the hydrated compound was investigated as a function of temperature at different relative humidities and parametrized on the basis of the Arrhenius equation. The dependence of both activation energy and pre-exponential factor on relative humidity was similar to that of ZrP. This suggests that in cerium phosphate also the proton conduction is due, for the most part, to the hydrated surface of the particles. 

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