Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses

Temperature modulated Alternating Differential Scanning Calorimetric (ADSC) studies show that Se rich Ge0.15Se0.85-xAgx (0 <= x <= 0.20) glasses are microscopically phase separated, containing Ag2Se phases embedded in a Ge0.15Se0.85 backbone. With increasing silver concentration, Ag2Se phase percolates in the Ge-Se matrix, with a well-defined percolation threshold at x = 0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume and micro-hardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The super-ionic conduction observed earlier in these glasses at higher silver proportions, is likely to be connected with the silver phase percolation.Comment: 4 pages, 7 figure

Anomalous electrical switching behaviour in phase-separated bulk

Bulk, Se-rich \chem{Ge_{0.15}Se_{0.85-{\it x}}Ag_{\it x}} ($0 \le x \le 0.20$) glasses show anomalous electrical switching behaviour which is attributed to difference in the thermal conductivities of \chem{Ag_{2}Se} inclusions and GeSe base glass. The present results also show that there is a sharp drop in switching voltage with silver addition, which is due to the higher metallicity of silver and the presence of \ab{Ag}^{+} ions. Further, the leveling of threshold voltage (V_\ab{T}) around $x = 0.10$, is associated with the percolation of \chem{Ag_{2}Se} phase in the Ge-Se matrix

Electrical switching and thermal studies on Ge22Te78-xIx chalcohalide glasses: The effect of iodine on network-topology

Investigations on the electrical switching behavior and thermal studies using Alternating Differential Scanning Calorimetry have been undertaken on bulk, melt-quenched Ge22Te78-,Is (3 <= x <= 10) chalcohalide glasses. All the glasses studied have been found to exhibit memory-type electrical switching. The threshold voltages of Ge22Te78-I-x(x) glasses have been found to increase with the addition of iodine and the composition dependence of threshold voltages of Ge22Te78-xIx glasses exhibits a cusp at 5 at.% of iodine. Also, the variation with composition of the glass transition temperature (Tg) of Ge22Te78-I-x(x) glasses, exhibits a broad hump around this composition. Based on the present results, the composition x = 5 has been identified as the inverse rigidity percolation threshold at which Ge22Te78-I-x(x) glassy system exhibits a change from a stressed rigid amorphous solid to a flexible polymeric glass. Further, a sharp minimum is seen in the composition dependence of non-reversing enthalpy (Delta H-nr) of Ge22Te78-I-x(x) glasses at x = 5, which is suggestive of a thermally reversing window at this composition. (C) 2007 Elsevier Ltd. All rights reserved

A sharp thermally reversing window in As45Te55−xIxAs_{45}Te_{55-x}I_x chalcohalide glasses revealed by alternating differential scanning calorimetry and photo thermal deflection studies

The composition dependence of different thermal parameters such as glass transition temperature, non-reversing enthalpy, thermal diffusivity etc., of bulk $As_{45}Te_{55-x}I_x$ chalcohalide glasses $(3\leq x \leq10)$, has been evaluated using the temperature modulated Alternating Differential Scanning Calorimetry (ADSC) and Photo Thermal Deflection (PTD) studies. It is found that there is not much variation in the glass transition temperature of $As_{45}Te_{55-x}I_x$ glasses, even though there is a wide variation in the average coordination number View the r source. This observation has been understood on the basis that the variation in glass transition temperature of network glasses is dictated by the variation in average bond energy rather than $\bar{r}$. Further, it is found that both the non-reversing enthalpy $(\Delta H_{nr})$ and the thermal diffusivity (\alpha) exhibit a sharp minimum at a composition x = 6. A broad hump is also seen in glass transition and crystallization temperatures in the composition range $(5\leq x \leq7)$ The results obtained clearly indicate a sharp thermally reversing window in $As_{45}Te_{55-x}I_x$ chalcohalide glasses around the composition x = 6

Signature of a silver phase percolation threshold in microscopically phase separated ternary Ge_0_._1_5Se_0_._8_5_-_xAg_x(0\not\leq x\not\leq 0.20) glasses

Temperature modulated alternating differential scanning calorimetric studies show that Se rich Ge_0_._1_5Se_0_._8_5_-_xAg_x(0\not\leq x\not\leq 0.20) glasses are microscopically phase separated, containing $Ag_2Se$ phases embedded in a Ge_0_._1_5Se_0_._8_5 backbone. With increasing silver concentration, $Ag_2Se$ phase percolates in the Ge–Se matrix, with a well-defined percolation threshold at x=0.10. A signature of this percolation transition is shown up in the thermal behavior, as the appearance of two exothermic crystallization peaks. Density, molar volume, and microhardness measurements, undertaken in the present study, also strongly support this view of percolation transition. The superionic conduction observed earlier in these glasses at higher silver proportions is likely to be connected with the silver phase percolation

Anomalous electrical switching behaviour in phase-separated bulk Ge-Se-Ag chalcogenide glasses

Bulk, Se-rich $Ge_{0.15}Se_{0.85-x}Ag_x (0 \le \times\le 0.20)$ glasses show anomalous electrical switching behaviour which is attributed to difference in the thermal conductivities of $Ag_2S_e$ inclusions and GeSe base glass. The present results also show that there is a sharp drop in switching voltage with silver addition, which is due to the higher metallicity of silver and the presence of $Ag^+$ ions. Further, the leveling of threshold voltage $(V_T)$ around x = 0.10, is associated with the percolation of $Ag_2S_e$ phase in the Ge-Se matrix

Functionally Expanded Phase-Change Memory: Experiments on Light Influence on Threshold Voltage

We describe the first experimental results of a light influence on the threshold voltage Vt in new ternary lead-free telluride compound (labeled as SA1). Reduction of Vt on about 35% in SA1 illuminated by Ar ion laser to compare dark Vt is discovered. More than 10,000 switching cycles without degradation have been recorded. Variation of the laser power allows achieving Vt reduction in SA1 down to 40% from the dark level. This is the largest change of Vt known for amorphous chalcogenides. It opens new horizons for chalcogenide functionally expanded phase change memory. Some ideas about the mechanism of the observed effect, related with the photo-generation of charge carriers and possible mechanisms of transition from OFF state to ON state, are discussed

Photo-thermal deflection and electrical switching studies on Ge–Te–I chalcohalide glasses

Measurements on thermal diffusivity $(\alpha)$ and electrical switching studies have been undertaken on bulk, melt-quenched $Ge_{22}Te_{78-x}I_x (3\leq x \leq10)$ chalcohalide glasses. The thermal diffusivity values of $Ge_{22}Te_{78-x}I_x$ glasses lie in the range $0.09–0.02 cm^2 s^{-1}$, and are found to decrease with increase in iodine content. The variation of $\alpha$ with composition has been understood on the basis of fragmentation of the Ge–Te network with the addition of iodine. The composition x = 5 $(\overline{r}_c = 2.39)$, at which a cusp is seen in the composition dependence of thermal diffusivity, has been identified to be the inverse rigidity percolation threshold of the $Ge_{22}Te_{78-x}I_x$ system at which the network connectivity is completely lost. Further, $Ge_{22}Te_{78-x}I_x$ glasses are found to exhibit memory-type electrical switching. At lower iodine concentrations, a decrease is seen in switching voltages with an increase in iodine content, in comparison with the switching voltage of the $Ge_{22}Te_{78}$ base glass. The observed initial decrease in the switching voltages with the addition of iodine is due to the decrease in network connectivity. An increase is seen in switching voltages of $Ge_{22}Te_{78-x}I_x$ glasses at higher iodine contents, which suggests the domination of the metallicity factor of the additive atoms on the switching voltages at higher iodine proportions. It is also interesting to note that the composition dependence of the threshold voltages shows a slope change at x = 5, the inverse rigidity percolation threshold of the $Ge_{22}Te_{78-x}I_x$ system

RIGIDITY PERCOLATION AND CHEMICAL THRESHOLD OBSERVED IN Ge7.5_{7.5}Asx_xTe92.5−x_{92.5-x} CHALCOGENIDE GLASSES STUDIED FROM ITS THERMAL AND OPTICAL PROPERTIES

Author Institution: Department of Physics, Faculty of Science in Physics and; Mathematics, University of Concepcion, Casilla160-C, Concepcion - Chile; Department of Instrumentation, Indian Institute of Science, Bangalore 560; 012-IndiaThe effect of rigidity percolation and chemical ordering on the thermal and optical properties of bulk Ge$_{7.5}$As$_x$Te$_{92.5-x}$ alloy glasses in the composition range, $17.5\leq$x$\leq 60$ [co-ordination number (&lt;r$>$), 2.35 to 2.75] was investigated. The thermal diffusivity of the samples were determined using the Photoacoustic (PA) technique. In the present work, the PA technique was employed in the reflection configuration and the corresponding PA signal was analysed using the Rosencwaig-Gersho theory for the case of backing-sample-air system with the experimental data being fitted using c2 minimization procedure for determining thermal diffusivity (a). The maximum value of a, 0.85x10-2 cm2/s, was observed for the sample with = 2.4, with a monotonic decrease in a for higher and lower &lt;r$>$ values except for a small hump of a = 0.44x10-2 cm2/s observed at &lt;r$>$ = 2.67. The variation in optical band gap with the coordination number was also investigated using standard Fourier transform near-infrared (FT-NIR) Spectroscopy. This study also showed a similar variations at &lt;r$>$ = 2.4 and &lt;r$>$ = 2.67. These observed anomalies from the behaviour of thermal diffusivity and optical band gap at these two coordination numbers are correlated to the rigidity percolation and chemical threshold respectively