EFFECT OF SURFACE CAPACITANCE ON THE DIELECTRIC BEHAVIOR OF FERROELECTRIC LEAD GERMANATE

The results of dc conductivity and the thickness dependence of the dielectric constant at 1, 10, and 100 kHz of ferroelectric lead germanate (Pb5Ge3O11) are reported for two electrode materials. The activation energy (dc) has been found to be 0.91 and 0.62 eV in paraelectric and ferroelectric phases, respectively. The dielectric constant decreases with decreasing thickness of the samples at all frequencies and the dielectric constant for evaporated gold is found to be higher than that for the silver-paint electrode. These results have been explained by assuming the formation of a homogeneous surface layer due to the potential barrier at the metal insulator junction. The surface capacitance shows a frequency dependence which may be due to the relaxation time associated with the surface layer. A possible mechanism for the formation of the surface layer is also discussed.