Temperature-induced phase transformations of the “glaserite” type zirconosilicate Na3HZrSi2O8·0.4H2O

DTA-TG and powder XRD analyses are used to study the occurring upon heating structural transformations of the “glaserite” type zirconosilicate Na3HZrSi2O8·0.4H2O. The title compound undergoes energetically favored irreversible topotactic dehydration within the temperature range 200 and 400 °C. Essential structural transformations occur only after 700 °C, however, the phase composition of the run-product strongly depends on the conditions of thermal treatment. In all cases the predominant phase at 1000 °C is the NASICON type zirconosilicate – Na4Zr2Si3O12. The concomitant compound is either Na2SiO3 or the parakeldyshite synthetic analog – Na2ZrSi2O7. The mechanism of structural transformation and certain structural relationships are discussed in terms of the crystal chemical peculiarities of the initial compound and the run-products.