A single-crystalline SrTiO3 (STO) (001) wafer with as-cut unpolished surface was investigated by means of Wide Angle X-ray Diffraction (WAXRD) in-situ under applying a d.c. electric field. The changes of WAXRD patterns measured in vicinity of 00l (l = 2 and 4) STO reflections give evidences of a tunable and reversible formation of domains with a distorted crystalline structure. Different time-voltage procedures were used. An enhancement of the structural distortions by the influence of X-ray irradiation is established. A diffusion nature of the phenomenon is discussed.