Ultraslow shock waves of electron density in LiNbO3 crystals

We show, experimentally and theoretically, that the application of modest voltages, U(0)=(0.1-1) kV, to LiNbO(3)Fe crystals at sufficiently high temperatures, T approximate to(550-700) degrees C, leads to the formation of ultraslow shock waves (moving discontinuities) of the electron density owing to the removal of electrons from Fe(2+) centers. Behind the sharp wave front, almost all iron centers are in the Fe(3+) state, the sample is optically transparent, and its transport properties are strongly modified. The front velocity decreases during the propagation; it is controlled by the electron mobility.