The structure of concentrated aqueous solutions of chromium nitrate and cerium chloride studied by X-ray diffraction and Raman spectroscopy

Abstract

Concentrated aqueous solutions of chromium nitrate and cerium chloride were investigated by X-ray diffraction and Raman spectroscopy. The X-ray diffraction patterns of two sets of solutions (1.60 up to 2.48 mol dm- 3 for chromium nitrate and 0.98 up to 2.81 mol dm- 3 for cerium chloride) display an intense maximum, prepeak, in the angular region about Q0 ~ 0.9 Å- 1 (Q = 4 [pi] sin [theta] / [lambda], [theta] being the diffracting angle). The value of Q0 corresponding to these maxima is proportional to the power 1/3 of the molar concentration. The proportionality coefficient has the value that should be observed for a close packing (fcc network) if assumed for cations. This study demonstrates, once more, the existence of an intermediate range order (up to ~ 10 Å) in very concentrated aqueous solutions of salts constituted by small ions of different valences, range order previously reported by these authors in many articles. Raman experiments are in consonance with X-ray diffraction results.