Characterization and thermal behavior of HGdP2O7 center dot 3H(2)O

Crystals of the trihydrated gadolinium diphosphate HGdP2O7. 3H(2)O were obt ained from a mixture of diphosphoric acid and gadolinium nitrate solutions. This salt was characterized by X-ray powder diffraction, IR spectroscopy a nd thermal analysis. IR spectroscopic study reveals the existence of the ch aracteristic band of the P2O7 group, the v(as)(POP) band, at 941 cm(-1) and the absence of the v(s)(POP) one. The thermal decomposition of HGdP2O7. 3H (2)O, which was followed by thermogravimetry and differential scanning calo rimetry, shows that the elimination of the crystallization water takes plac e in three stages between 71 and 500 degreesC. The overall DeltaH of the fi rst two dehydration were found to be 41.06 and 25.88 kJ/mol. New well-cryst allized hydrates HGdP2O7.1.5H(2)O and HGdP2O7.0.5H(2)O were obtained throug h heating HGdP2O7. 3H(2)O, respectively, at 145 and 280 degreesC. The anhyd rous HGdP2O7 salt, which was obtained by calcination of HGdP2O7. 3H(2)O at 530 degreesC, decomposes at 700 degreesC with loss Of P2O5 to give the gado linium diphosphate Gd-4(P2O7)(3). (C) 2001 Elsevier Science Ltd. All rights reserved.