Extended rigidity percolation and chemical thresholds in Ge-Te-Pb glasses as revealed by MDSC

Thermal analysis of Ge20Te80−xPbx (2≤x≤8) glasses has been undertaken using modulated differential scanning calorimetry (MDSC). The compositional dependence of thermal parameters is investigated. The crystallization temperatures (Tc) estimated from the total heat flow show detectable changes at compositions x=4, 6.5 and 7.5. Further, the heat capacity change at the glass transition temperature, measured from the reversible heat flow curve (ΔCpR), is found to exhibit a maximum and an inflexion at compositions x=4 and 6.5 and minimum at x=7.5, respectively. Also, the relaxation enthalpy, estimated from the area under the non-reversing heat flow curve (ΔHNR), exhibits similar features at the said compositions. From the observed MDSC results, it has been proposed that the compositions x=4 and x=6.5 denote to the onset and completion of rigidity percolation and x=7.5 corresponds to the chemical threshold of the system

Transient and steady state photoconductivity studies on bulk glasses and amorphous films of Ge-Te-Pb - Composition and spectral dependence

Transient photoconductivity studies have been undertaken on bulk Ge 20Te80-x Pbx glasses with varied lead content (2 ⤠x ⤠8); The composition dependence of normalized photoconductivity and photo-decay have been investigated upon white light incidence. The photoconductivity rise and its decay with time indicate that the process may best be understood in terms of the recombination within the localized states, Further, it has been found that the addition of lead results in an initial decrease in the photoconductivity, showing anomalous variations at compositions x = 5, 6.5 and 7.5. Steady state photoconductivity studies on amorphous Ge 20Te80-xPbx thin films (2 ⤠x ⤠8) have also been undertaken. The intensity dependence of steady state photoconductivity indicates the existence of continuous distribution of localized states in the mobility gap of this material, Further, the spectral dependence of photoconductivity has been studied using various interference filters. The composition dependence of steady state photoconductivity due to white light incidence, shows pronounced anomalies at x = 5, 6.5 and 7.5, Based on the present photoconductivity studies and other investigations, it has been proposed that the rigidity percolation occurs in Ge20Te 80-x Pbx glasses, over an extended composition region with the composition x = 5 (xc1) and x = 6.5 (xc2) being the onset and completion of the rigidity percolation. The composition x = 7.5 corresponds to the chemical threshold of the system

Electrical switching studies of lead-doped germanium telluride glasses

Samples of bulk Ge20Te80-xPbx(2 ⤠x ⤠8) glasses have been prepared by melt quenching and their electrical switching behavior has been investigated as a function of lead content and sample thickness. The samples are found to exhibit a threshold type of switching. The switching voltages are found to decrease with increase in lead content and they show an anomaly at the composition x = 5 and a minimum at the composition x = 7.5 respectively. The samples are found to withstand about 28 switching cycles, before latching permanently to the ON state