It has been shown that the introduction of thulium impurity into the crystals of strontium barium (SBN:61) niobate leads to an increase in the dielectric constant value and the blur region of the phase transition. External field polarization partially stabilizes the polar state of the samples, however, the heterogeneous distribution of polarization across the thickness of the studied samples indicates the existence of regions with a developed domain structure characteristic of highly doped crystals.