The glass to NZP crystal transformation in a mixed alkali germano-phosphate glass matrix

A mixed alkali germano-phosphate glass composition (Li0.5Na0.5Ge2(PO4)3) has been prepared and characterized. The crystallization mechanism of a NZP-type phase, the nucleation rate and the non-isothermal kinetic parameters have been studied by differential thermal analysis (DTA).The plot of the DTA peak height versus the glass particle size has shown a great tendency for surface crystallization. The nucleation rate type curves have given a maximum at 465 ± 2 °C and confirmed that nucleation was instantaneous at this temperature. Furthermore, the average value of the Avrami exponent (5.4 ± 0.4) has revealed a tri-dimensional growth controlled by the development of the glass–crystal interface with a decreasing nucleation rate in the temperature range explored. From non-isothermal experiments, the apparent activation energy for the overall crystallization phenomenon has been founded in the range 260–273 kJ/mol whereas the activation energy for crystal growth was 488 ± 6 kJ/mol.