1. Identification of complex ions of niobium(V) in hydrofluoric acid solutions by Raman and infrared spectroscopy;Keller;J. Inorg. Chem.,1963
2. A study by Raman spectroscopy of complex ions formed by tantalum (V) in the system Ta(V)–HF–NH4F–H2O;Keller;J. Inorg. Chem.,1966
3. Vibrational spectra of niobium and tantalum complexes in hydrofluoric acid solutions;Tsikaeva;Zh. Obshch. Khim.,1987
4. Complexation of niobium(V) in hydrofluoric acid solutions in the presence of fluorides of alkali metals and ammonium;Tsikaeva;Zh. Neorg. Khim.,1989
5. A.G. Babkin, V.G. Maiorov, A.I. Nikolaev, Extraction of niobium and tantalum and other elements from fluoride solutions, Nauka, Leningrad, 1988 (in Russian).