RADIATION-INDUCED CHANGES IN THE STRUCTURE AND FERROELECTRIC PROPERTIES OF Pb5Ge3O11 SINGLE CRYSTALS

Perfect stoichiometric Pb5Ge3O11 single crystals are irradiated with Co-60 gamma-rays (1.10(6) Rad) and high-energy electrons (0.13 e/cm(2), 0.89 e/cm(2), 2.18 e/cm(2), 3.07.10(18) e/cm(2)) at the Karpov Institute of Physical Chemistry. Changes in the structural and ferroelectric properties of the crystals are traced depending on the irradiation type and dose. Dielectric spectroscopy and second harmonic generation of laser radiation are used to determine the ferroelectric phase transition temperature T-C. X-ray diffraction experiments are carried out on a Bruker D8 QUEST diffractometer with a PHOTON-II detector (MoK alpha, radiation, 295 K). Based on the experimental structural amplitudes the crystal structures of the crystals before and after irradiation are solved and refined. Structural characteristics of the non-irradiated crystal are consistent with the previously reported data at the achieved significant improvement of their accuracy (R(F > 2 sigma(F)) = 0.028). Despite radiation defects introduced, Pb5Ge3O11 single crystals retain the crystal structure and ferroelectric properties. It is shown that irradiation performed maintains the polar structure at 295 K and causes changes in atomic displacements of separate atoms. It is supposed that a radiation-induced change in the Pb5Ge3O11 structure is of the high-temperature type and forms a new structural state close to a high-temperature modification of a non-irradiated Pb5Ge3O11 crystal. Irradiation leads to a gradual decrease in distortions and structure symmetrization. It is important that the kinetics and final products of these processes appreciably differ from those observed only upon thermal impacts. Polar shifts are calculated, and their dependence on the irradiation dose indicates a tendency to a decrease in polar shifts in lead germanate ferroelectric during irradiation.