Investigation of the KNd(SO4)2<middle dot>H2O-SrSO4<middle dot>0.5H2O System

The cocrystallization of potassium, neodymium, and strontium sulfates from aqueous solutions has been studied using X-ray powder diffraction, thermogravimetry, energy-dispersive X-ray spectral analysis, and electron microscopy. Extensive solid solutions based on trigonal KNd(SO4)(2)& sdot;H2O have been found to exist in the concentration range 100-20 mol % of the KNd(SO4)(2)& sdot;H2O-SrSO4 & sdot;0.5H(2)O system. The unit cell parameters of the solid solutions have been determined. Two phases have been discovered: trigonal KNd(SO4)(2)& sdot;H2O (space group P3(1)21) and monoclinic KNd(SO4)(2)& sdot;H2O (space group P2(1)/c(1)). The heterovalent substitution scheme 2Sr(2+) -> K+ + Nd3+ stabilizes the structure of solid solutions based on the isostructural KNd(SO4)(2)& sdot;H2O and SrSO4 & sdot;0.5H(2)O trigonal phases.