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 Q 0 ∼ 0.9 Å − 1 ( Q = 4 π sin θ / λ, θ being the diffracting angle). The value of Q 0 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.