Characterization and thermal behavior of HGdP 2O 7·3H 2O

Abstract

Crystals of the trihydrated gadolinium diphosphate HGdP 2O 7·3H 2O were obtained from a mixture of diphosphoric acid and gadolinium nitrate solutions. This salt was characterized by X-ray powder diffraction, IR spectroscopy and thermal analysis. IR spectroscopic study reveals the existence of the characteristic band of the P 2O 7 group, the ν as(POP) band, at 941 cm −1 and the absence of the ν s(POP) one. The thermal decomposition of HGdP 2O 7·3H 2O, which was followed by thermogravimetry and differential scanning calorimetry, shows that the elimination of the crystallization water takes place in three stages between 71 and 500°C. The overall ΔH of the first two dehydration were found to be 41.06 and 25.88 kJ/mol. New well-crystallized hydrates HGdP 2O 7·1.5H 2O and HGdP 2O 7·0.5H 2O were obtained through heating HGdP 2O 7·3H 2O, respectively, at 145 and 280°C. The anhydrous HGdP 2O 7 salt, which was obtained by calcination of HGdP 2O 7·3H 2O at 530°C, decomposes at 700°C with loss of P 2O 5 to give the gadolinium diphosphate Gd 4(P 2O 7) 3.