Abstract Barium titanate with powder particles having a diameter of about 50 nm, which was prepared by sol–gel-hydrothermal reaction, was studied using several experimental techniques for the determination of the crystalline phase and purity of synthesized BaTiO 3 . The results of XRD and Raman spectroscopy were contradictory with respect to the nature of the formed phase for the barium titanate nanocrystals. The first indicated the formation of a cubic phase and the second indicated that was tetragonal. Thus, we use a combination of experiments, especially Raman spectroscopy supported by density functional theory calculations and measurement of the ferroelectric behavior, which showed the formation of a tetragonal phase. In addition, from theoretical calculations suggested that the ferroelectric nature, present only in the tetragonal phase, can arise from a small displacement of the titanium atom along the Z -axis from ⩾0.5 pm, leaving from a cube phase to obtain pseudo cubic or slightly tetragonal phases.