Abstract A series of Ba xSr 1−x(NO 3) 2 crystals have been grown from aqueous solutions with different initial Ba 2+/Sr 2+ ratios. These crystals were characterized by powder X-ray diffraction. All diffraction data were well indexed according to the simple cubic structure, and the variation of lattice constants with the concentration of Ba 2+ in the crystals accorded quite well to Vegard’s Law. The composition of the Sr(NO 3) 2 crystal doped with Ba 2+ was studied with an electron microprobe. It was found that Ba 2+ was enriched in the 100 sectors. The quality of the crystals with different composition estimated by the high-resolution X-ray diffraction indicated that the second cation added to the crystalline phase degrades the crystalline quality of the crystals. Equilibrium behavior in the Ba(NO 3) 2–Sr(NO 3) 2–H 2O system was analyzed using Lippmann’s phase diagram, and the equilibrium distribution coefficient D Ba = 769.2. This large value of D indicates that the Ba 2+ ion is drastically preferentially partitioned towards the solid phase.