Variations of the Bragg diffraction angle induced by electric fields on piezoelectric single crystal were investigated with the aim of exploiting such crystals for novel neutron devices. A (1- x)(Pb(Mg 1/3Nb 2/3)O 3)- x(PbTiO 3) (PMN-PT) single crystal with strong piezoelectric characteristics was used in the experiment. The sample was poled along <0 0 1>direction before the experiment. In the course of diffraction measurements, a 0.3° change was observed in the diffraction angle at the maximum induced by the electric field. The diffraction angle variation shows time-dependent behavior, which can be well described using a single exponential decay limited to a saturated value. This effect is considered a result of a change of the domain structure brought about through long-term application of an electric field for several hours. The obtained preliminary results confirmed the possibility of using a ferroelectric crystal as a neutron optical device.