Infrared spectrum of crystalline and glassy pyrophosphates : preservation of the pyrophosphate group in the glassy structure

Two families of pyrophosphates, namely MIMIIIP2O7 and M2IMIIIP2O7 have been synthesized and investigated by IR spectroscopy, the emphasis being put on the anti-symmetric and symmetric frequencies of the P-O-P bridge. These bands are still present in the spectra of the glasses obtained by rapid quenching of the corresponding melts. This strongly suggests that, contrarily to expectations, the pyrophosphate group is essentially conserved in the glassy structure. This interpretation is supported by the investigation of glassy phases whose composition extend from meta- to ortho-phosphate.