DSC studies were performed to investigate the non-isotenal behavior of the glass samples. DSC studies were performed to investigate the non-isothermal behavior of the glass samples. The nature of the glass transition is very complex and even now poorly understood.
The heat capacity Cpg of the glass differs from the heat capacity Cn of the supercooled liquid. The glass transition temperature Tg depends on the rate of cooling of the supercooled liquid [1]. The viscosity of glass-forming liquids changes very rapidly in the vicinity of the glass transition temperature.
C. electrical conductivity of an amorphous semiconductor can be understood from the
Majority charge carrier reversal (MCCR) phenomenon
In n-type glass, the ratio of the higher valence to the lower valence, viz. In n-type glass, the ratio of the higher valence to the lower valence, viz. The change in the optical band gap was attributed to distortion of the field around the vanadium ions accompanying matrix modification.
Consequently, the entire phonon density of states appears in the infrared and Raman spectra resulting in a broad band instead of the discrete line. In the weak absorption tail region, it is found that the strength and the shape of the absorption tail depend on the. In the weak absorption tail region, the strength and shape of the absorption tail is found to depend on the preparation, purity and the thermal history of the material [99].
The sample holder which is inside the brass cylinder, consists of a copper block of j
The extent of the glass-forming region (GFR) of the V 2 O 5 -Sn 0 -TeO 2 system is not known. Glass samples of the system xV2O5.20SnO.(80-x)TeO2 (18 < x < 50) used in the present studies were prepared using the melt-quenching technique. The experimental observation of the glass transition temperature (Tg) is necessary to classify the sample as a glass.
This observation predicts that the thermal conductivity of the glasses increases as the V2O5 mol % increases in the xV2O5.20SnO.(80-x)TeO2 (18 From the density data, the molar volume of glasses was calculated (table 3.2) using equations (2.8) and (2.9). They reported a decrease in V-O bond covalency with an increase in V2O5 content in this glass system. Increasing the number of non-bridging oxygens decreases the average chemical bond strength of the glass, which in turn shifts the absorption edge to the longer wavelength side [18]. An increase in the number of non-bridging oxygens reduces the average chemical bond strength of the glass which in turn shifts the absorption edge to longer wavelength side [18]. When the number of non-bridging oxygen in a glass increases, the elastic moduli of the glass decrease [35]. When the number of non-bridging oxygen in a glass increases, the elastic moduli of the glass become. Thus, a sudden change in glass brittleness is observed close to the composition at which MCCR occurs in these glasses. The variation of the excess heat capacity at Tg of these glasses with composition shows an abrupt change in the brittleness of the glasses at x = 30 mol% V2O5. Thus, a sudden change in glass fragility is observed close to the composition at which MCCR occurs in these glasses. To understand the conduction mechanism in the glasses of this system, the data are analyzed in relation to the Mott and Austin model. The calculated N and R values are shown in table 3.4 (the glass density values required for the calculation are taken from table 3.2). Inset shows a typical fit of the data to relationship (3.2) (Only one in ten data points is plotted to improve clarity of the figure). The calculated N and R values are shown in table 3.4 (the values for glass density required for leaching are taken from table 3.2). Inset shows a typical fit of the data to relation (3.2) (Only one out of ten data points is plotted to improve the clarity of the figure). The parameter W can be calculated from the slope of the least-squares fit of In(aT) versus 1000/T plots for all glasses. The non-adiabatic mobility for the rest of the glasses (shown in table 3.5) was calculated using the relation [68],. The parameter W can be calculated from the slope of least squares fitted to In(oT) versus 1000/T plots for all glasses. Therefore, the conductivity data in the low temperature region were analyzed in light of the Mott-Austin VRH mechanism. The change in slope in the graphs in Figure 3.18 has been interpreted [73, 78] as the signature of the conductance change from SPH to VRH. The slope change in the plots shown in Figure 3.18 has been interpreted [73, 78] to be the signature of the conductance change from SPH to VRH. Density, microhardness and band gap measurements show the following features The signature of MCCR is more pronounced in chalcogenide glasses such as Bi-Ge-Se [156. The thermoelectric power measurements show the following features; As explained in the previous chapter, the glassy nature of the samples was limited to the observation of the glass. From the density data, the molar volume of the glasses was calculated using the relationship (2.9). The gram molecular weight was calculated. Density and molar volume data of the V205-Ca0-P2O5 glasses are shown in Table 4.2 (previously reported data are in parentheses). Therefore, overall, the density of the glass increases with increasing V2O5 mol % content. The absorption data of the glasses were recorded in the wavelength range from 190 nm to 800 nm. The presence of more non-bridging oxygens reduces the average chemical bond strength of the glass. This reduces the elastic moduli leading to a decrease in the microhardness of the glass {equation (1.42)}. Since Tg decreases with increasing V2O5 content (table 4.3), the microhardness is expected to decrease with increasing V2O5 content in this glass system. Inset shows a typical fit of the data to ratio (4.3) (Only one out of ten data points is plotted to improve the clarity of . the figure). The parameter W was calculated from the slope of the least squares fit to In(aT) versus 1000/T plots (table 4.4). The parameter W was calculated from the slope of the least squares fit to In(aT) versus. The thermoelectric power measurements on the different compositions of glasses of the V205-Ca0-P205 glass system show the following characteristics:. Measurements of thermo-electric power in different compositions of glasses of the V205-Ca0-P20s glass system show the following characteristics: The thermal activation energy AEs of these glasses decreased as V2O5 content was increased, as shown by figure 5.5, suggesting that the thermal conductivity of the glasses increases with an increase in V2O5 content. The density of the glass increases as the V2O5 content in the glass is increased and showed the maximum value at the composition with x = 20 mol V. The thermal activation energy AEs of these glasses decreased as the V2O5 content increased, as shown by figure 5.5, which suggests that the thermal conductivity of the glasses increases with an increase in V2O5 content. The density of the glass increases as the V2O5 content in the glass increases and showed a maximum value at the composition with x = 20 mol% V2O5. This explains the observed variation in microhardness of the V205-Ca0-B203 glasses with V2O5 content, shown in Figure 5.8. So despite an increase in molar volume when a V2O5 molecule replaces a B2O3 molecule, the total mass of the glass increases overall. The molar volume of the glass increases sharply [figure 5.6] after 20 mol % V2O5 showing that glassy network expands more rapidly after this composition. This leads to a decrease in the density of the glass as illustrated by the weak maximum in the density. This accounts for the observed variation in microhardness of the V205-Ca0-B203 glasses with V2O5 content plotted in figure 5.8. This low value of ACp is a result of the weak glass transition that these glasses exhibit. This low value of ACp is a result of the weak glass transition that these glasses exhibit. 400K), polaron bandwidth j, the parameter O. The dcvalion of the conductivity data at lower temperatures f.„,. Figure 5.15) suggests that the conduction mechanism is different. Therefore, the low-temperature conductivity data were analyzed in light of the Mott-Austin VRH mechanism. In addition to the specific features that arise due to the constitution of the individual glass system, the present studies revealed several features that were commonly observed in all three glass systems in specific compositions. The activation energy for thermal conduction AEj, of the three glass systems (the figure shows a significant change in the slope in the composition in which the inversion of the majority of the charge carrier was observed. Analysis of electrical conductivity based on "the Mott-Austin model found that all glasses in all three systems showed SPH conduction mechanism at high temperatures and VRH conduction mechanism at low temperatures. This observation is not surprising since the MCCR accompanies a change in the vanadium ion ratio. This subtle slope change in the microhardness value at the MCCR composite indicates a change in the average bond strength of the glass at tKis. Since ACp can be correlated with the brittleness of the glass, this observation is quite interesting. The abrupt change in glass brittleness in the MCCR composition suggests that the MCCR composition undergoes the minimum. The strong dependence of the electrical properties on the vanadium ion ratio is an interesting result of this research work. The activation energy for the thermal conduction AEs of the three glass systems (figure shows a marked change in slope in the composition in which the majority charge carrier inversion was observed. This finding is not surprising since the MCCR follows a change in the vanadium ion ratio. Since these parameters are sensitive to the vanadium ion ratio, they also bear the signature of the MCCR phenomenon. This subtle change in the slope of the microhardness values in the MCCR composition indicates a change in the average bond strength of the glass therein. The abrupt change in the fragility of the glass in the MCCR composition suggests that the MCCR composition is undergoing a 'mfiii'mold.Density, microhardness and band gap measurements show the following features;
Density, microhardness and band gap measurements showed the following features
The thermoelectric power measurements revealed the following aspects
