Infrared spectroscopy and X-ray diffraction studies of the Ca2P2O7/Na4P2O7 system

Sintered composites I(x)Na4P2O7, (1-x)Ca2P2O7], where x varies from O to I, have been heat treated at 850 degrees C during 24 hours. They were studied by electrical measurements and cationic mobilities was shown up. In this paper, we present the results of investigations made by X-ray diffraction and Fourier Transform Infra-Red spectroscopy, in order to better understand the previously observed ionic conductivities. The study of the cell parameters is in agreement with the phase diagram. A monoclinic cell and space groups are proposed for the intermediate phase Na2CaP2O7. The F.T.I.R spectrum of the Na2CaP2O7 phase is discussed as compared to the spectra obtained from the other pyrophosphates. The local and long range structures of both Na2CaP2O7 and Na4P2O7 are probably similar. Finally, no solid solution has been evidenced to interpret the observed ionic mobilities.