Phase formation in the NiSO4-CoSO4-H2O system and specifications in the structures of single crystals of CoxNi(2-x)(SO4)2<middle dot>12H2O

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)<middle dot>12H(2)O, have been studied. The crystallization regions of tetragonal NiSO4<middle dot>6H(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)<middle dot>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)<middle dot>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)<middle dot>12H(2)O crystals are a series of solid solutions based on the crystal structure of CoSO4<middle dot>6H(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)<middle dot>12H(2)O crystals are a promising material for optical filters used in photonics.