Ionic conductivity and Raman investigations on the phase transformations of Na 4P 2O 7

Abstract

The ionic conductivity and thermo-Raman spectra of anhydrous sodium pyrophosphate Na 4P 2O 7 were measured dynamically in the temperature range from 25 to 600 °C with a heating rate of 2 °C min −1 to understand the structural evolution and phase transformation involved. The DSC thermogram was also measured in the same thermal process for the phase transformation investigation. The spectral variations observed in the thermo-Raman investigation indicated the transformation of Na 4P 2O 7 from low temperature phase ( ε) to high temperature phase ( α) proceeded through pre-transitional region from 75 to 410 °C before the major orientational disorder at 420 °C and minor structural modifications at 511, 540 and 560 °C. The activation energies and enthalpies of the proposed phase transformations were determined. The possible mechanism for temperature dependent conductivity in Na 4P 2O 7 was discussed with the available data.