In this work, the formation of CuB₂O₄:Ni crystals in fluxes based on Li₂WO₄–Bi₂O₃–WO₃ solvents was studied. The crystallized phases were studied with respect to the WO₃ content and the mode of crystal holder insertion. A distinctive feature of the used flux growing mode is the metastable nature of nucleation: the desirable phase was obtained by using a super-cooled crystal holder – under insertion of a crystal holder cooled down to temperatures of the metastable zone. By powder X-ray diffraction, the composition of the obtained samples was analyzed. IR reflection and transmission spectra of the as-synthesized single crystals were recorded and analyzed in comparison with that of “pure” CuB₂O₄.