Thermal, structural, and defect studies on Pb modified GeSe glasses

We report the detailed thermal, structural, microstructural and electrical transport studies on PbxGe42 − xSe58 with (0 ≤ x ≤ 20) glasses. The influence of Pb content on thermal and local atomic structure and its qualitative consequences on the electronic properties has been elucidated. The composition dependent variation of glass transition temperature (Tg), change in specific heat capacity at the glass transition (ΔCp) and non-reversing enthalpy change (ΔHNR) complement with each other for enabling the role of Pb content on structural relaxation behavior of these glasses. The Raman spectroscopic studies reveal the presence of different structural species and its variation with Pb content, i.e. pronounced decrease in the amount of ethane-like structural units with the incorporation of Pb content. The addition of Pb content into Ge42Se58 glass, the network connectivity becomes loosened due to the depolymerization. The observed Raman band position of ethane-like structural units show noticeable blue shift with an increase of Pb content, which dictates the development of stress in the network structure caused by the predominant ionic character. The microstructural studies by positron annihilation life-time spectroscopy reveal the nature of defect states and its variation with Pb content. The composition dependent dc conductivity and its activation energy shows marked change across the p-n transition threshold due to the change in the charged defect concentration. The influence of local atomic structure and nature of defect states responsible for the carrier type reversal (CTR) has been discussed.