The properties of oxygen depleted ceramic Pb(Zr0.65 Ti0.35)O3 1wt. % Nb2O5 surface layers

Abstract

The properties of oxygen depleted ceramic Pb(Zr0.65 Ti0.35)O3 + lwt. % Nb2O5 surface layers were studied using the Hall effect, conductivity versus temperature measurements and capacitance and dissipation factor versus frequency measurements. Surface layers having thicknesses (measured via an electron microscope) between 25 and 250 microns were grown by rapidly heating a cleaned and etched ceramic PZT pellet to 500°C in a quartz chamber filled with oxygen free argon gas. In this manner the virgin PZT is transformed from a highly compensated p-type semiconductor having a conductivity of less than 10-11 (ohm-cm)-1 [1] to an n-type semiconductor having conductivities of 10-5 to 10-8 (ohm-cm)-1 by the introduction of oxygen defect states which act as electron donors.The conductivity versus temperature measurements for several samples indicate that the electron donor level is between 0.22 eV and 0.28 eV. This is compared to the band gap energy of approximately 3.0 eV. Using the Hall effect the semiconductor was verified to be n-type and the mobility at room temperature was found to be 0.2 × 0.12 cm2/volt-sec. The capacitance and dissipation factor versus frequency data indicate that the relative dielectric constant in the reduced PZT is less than the dielectric constant of 480 for virgin PZT. The measurements also reveal that the dielectric properties of the PZT substrate are not significantly perturbed during the depletion process. The dielectric properties were investigated by using a simple double layer series-parellel resistance-capacitance model.