“…Raman spectra and PILS pictures of lithium niobate crystals of stoichiometric composition, as well as congruent crystals doped with cations listed above were investigated earlier in Refs. [2,4,[7][8][9][10][11][12][13][14]. Optical quality control and structural homogeneity of the grown crystals were carried out by laser conoscopy and electron spectroscopy.…”