Structure-directing effect of phyllosilicates on the synthesis of y-Y2Si2O7. Phase transitions in Y2Si2O7

This paper describes the low temperature hydrothermal synthesis of y-Y2Si2O7 from a layered silicate (2 ∶ 1 clay), a precursor which acts as a structure-templating agent. Both the transformations undergone by the clay during the hydrothermal process and the new products formed at different reaction stages have been characterised at both long and short range orders. Secondly, the influence of the aluminium content of the clay on the stability of y-Y2Si2O7 has been investigated. For this purpose, another layered clay, containing nominally no Al, has been submitted to the same hydrothermal treatment as the previous one. The results indicate that the amount of aluminium present in the starting material assists the stabilisation of y-Y2Si2O7. The behaviour of y-Y2Si2O7 with increasing temperature has been studied and the sequence of polymorphs and transition temperatures are reported and compared with those found in the literature.