Phase formation in the NiSO4-CoSO4-H2O system and specifications in the structures of single crystals of CoxNi(2-x)(SO4)212H2O

The conditions of phase formation in the ternary water-salt system comprised of NiSO4-CoSO4-H2O at 25 degrees C, which is the first step for the creation of structurally perfect mixed crystals CoxNi(2-x)(SO4)(2)12H(2)O, have been studied. The crystallization regions of tetragonal NiSO46H(2)O in the NiSO4:CoSO4 ratio range from 100:0 to 95:5 mass% and monoclinic solid solution of CoxNi(2-x)(SO4)(2)12H(2)O in the NiSO4:CoSO4 ratio range from 95:5 to 0:100 mass% were delineated. A set of CoxNi(2-x)(SO4)(2)12H(2)O single crystals in the range of 0.05 <= x <= 1.95 was obtained. The crystal structures of the samples with x values equal to 1.5, 1.13, and 0.56 have been studied. The CoxNi(2-x)(SO4)(2)12H(2)O crystals are a series of solid solutions based on the crystal structure of CoSO46H(2)O. The transmission spectra in the lambda range of 200-800 nm were studied for the obtained crystal samples. A significant decrease in the intensity of the transmission bands in the visible region of the spectrum was observed due to the simultaneous presence of [Ni(H2O)(6)] and [Co(H2O)(6)] complex octahedra in the crystal structures. Consequently, the CoxNi(2-x)(SO4)(2)12H(2)O crystals are a promising material for optical filters used in photonics.

Automated summary

This study investigated the conditions for phase formation in the ternary water-salt system NiSO4-CoSO4-H2O at 25 degrees C, which is the first step towards creating structurally perfect mixed crystals CoxNi(2-x)(SO4)(2)12H(2)O. The regions of crystallization for tetragonal NiSO46H(2)O and monoclinic solid solution of CoxNi(2-x)(SO4)(2)12H(2)O were determined based on the NiSO4:CoSO4 mass ratio. Additionally, a set of CoxNi(2-x)(SO4)(2)12H(2)O single crystals were obtained in the range of 0.05 <= x <= 1.95, and the crystal structures of samples with x values of 1.5, 1.13, and 0.56 were studied. The CoxNi(2-x)(SO4)(2)12H(2)O crystals are solid solutions based on the crystal structure of CoSO46H(2)O, and they showed significant decreases in transmission band intensity in the visible region of the spectrum, making them promising materials for optical filters in photonics.