Influence of Ag, Cd or Pb Addition on Electrical and Dielectric Properties of Bulk Glassy Se-Ge

Abstract

Bulk glassy samples of Se0.7Ge0.3 and Se0.7Ge0.25X0.05 (X = Ag, Cd or Pb) chalcogenide glass have been prepared by melt-quenching method. The studied compositions were examined in powder form by x-ray diffraction analysis. The direct-current (dc) conductivity $$ \sigma_{\rm{dc}} $$ was measured for bulk samples in the temperature range from 303 K to 433 K, revealing enhancement with temperature for all samples. The results indicate two values of activation energy ( $$ \Delta E_{{\sigma_{1} }} $$ and $$ \Delta E_{{\sigma_{2} }} $$ ) due to two conduction mechanisms. Measurements of the alternating-current (ac) conductivity $$ \sigma_{\rm{ac}} \left( \omega \right) $$ and dielectric properties for bulk samples were carried out in the temperature range from 303 K to 433 K and frequency range from 1 kHz to 1 MHz. The ac conductivity $$ \sigma_{\rm{ac}} \left( \omega \right) $$ was temperature dependent and proportional to $$ \omega^{S} $$ , where $$ S $$ is the frequency exponent, which reduced with rising temperature, and $$ \omega $$ is the angular frequency. These results are discussed based on a correlated barrier hopping model. The calculated values of the maximum height of the barrier $$ W_{\rm{M}} $$ for each composition are consistent with carrier hopping over a potential barrier. The density of localized states $$ N\left( {E_{\rm{F}} } \right) $$ at the Fermi level lay in the range from 1019 eV−1 cm−3 to 1020 eV−1 cm−3, and increased with temperature. The dielectric constant $$ \varepsilon_{1} \left( \omega \right) $$ and loss $$ \varepsilon_{2} \left( \omega \right) $$ increased with temperature but decreased with frequency. The values of $$ \sigma_{\rm{dc}} $$ , $$ \sigma_{\rm{ac}} \left( \omega \right) $$ , $$ \varepsilon_{1} \left( \omega \right) $$ , and $$ \varepsilon_{2} \left( \omega \right) $$ increased with temperature and with addition of Ag, Cd or Pb. The observed increase was greater for Se0.7Ge0.25Pb0.05 than for Se0.7Ge0.25Cd0.05, which was greater than for Se0.7Ge0.25Ag0.05.