The relation between the dielectric dispersion and distribution of ions and vacancies in the unit cell of oxides of the K2-xPb4LixNb10O30 composition

The frequency and temperature dependencies of the complex dielectric permit tivity of the TWB oxides K2-xPb4LixNb10O30 with x = (0,4-1,6) were studied. A typical feature of all the oxides is the presence of ferro-paraelectric phase transitions. In the region of infra-low frequencies, for the oxides w ith x=1.2-1.6 one can observe relaxation dispersion of the dielectric permi ttivity. A mechanism is proposed which explains the dielectric dispersion, viz. thermoactivated jumps of Pb ions performed in 5-angular channels of th e TWB-structure from one unit cell to the neighboring one under the action of an electric field along the c axis. The distribution of the ions of meta ls (K, Ph, Li) and vacancies over the positions in the TWB unit cell was de termined from the dielectric spectra of oxides in accordance with a general chemical formula of the TWB unit cell.