Cathodic processes in the CsCl-K3TaOF6 melt were studied in the temperature range 650-850 degrees C by cyclic voltammetry. It was shown that electrolysis of the CsCl-K3TaOF6 melt led to the formation of several phases containing tantalum on the molybdenum cathode. The variations of the cathodic products at different concentrations of K3TaOF6 and temperatures were determined. It was found that TaO crystallizes at the cathode as nanoneedles to 1200 nm in length with a cross-section around of 100 nm together with other tantalum compounds. Monoxide of tantalum was obtained by electrolysis of molten salts only at temperatures below 810 degrees C. Monoxide of tantalum is a high-pressure phase, so it was confirmed once more by electrolytic synthesis of TaO that an effect similar to the action of high pressure occurs during electrolysis. (C) The Author(s) 2017. Published by ECS. All rights reserved.