Vibrational behaviour of K2HPO4, K(2)HPO(4 center dot)3H(2)O and their deuterated derivatives with temperature

The infrared and Raman spectra of K2HPO4, K2HPO4. 3H(2)O and their deuterat ed derivatives were investigated between 10 and 550 K in the 4000-10 wavenu mber range. For the anhydrous compound, two reversible phase transitions we re evidenced and characterised at 150 and 450 K (180 and 450 K for the deut erated one). Above 450 K, the crystal is disordered, and the HPO42- ions be come spectroscopically equivalent. However, the strength of the hydrogen bo nds remains practically the same as in the other phases and protonic conduc tion was not evidenced. K2HPO4. 3H(2)O shows two low temperature second ord er phase transitions at 165 and 200 K. These transitions consist of an orde ring of the water molecules which are dynamically disordered at room temper ature. The reversible anhydrous-trihydrate transition at 330 K is explained by rotational motions of the HPO4 entities inside similar crystal framewor ks. (C) 2001 Elsevier Science B.V. All rights reserved.