الفهرس 
THEORETICAL BACKGROUNDOnly 14 pages are availabe for public view
 |  | from | 172 |  |  |
| | | from | 172 | | |
Abstract
The thesis aimstoprepareand studythe physical, optical and electrical propertiesof sodium phosphate glassesdopedwith different concentrations oflithium oxide(Li2O)with concentrationranging from0- 35 mol%. Also, the thesis includes the transformation of the prepared glasses to their corresponding glass-ceramic derivatives by adding copper oxide (CuO) in small proportions ranging from 0 – 1 mol% and study the effect of annealing on as prepared glass samples.
Transparent glasses of 55 P2O5 - (45-x) Na2O –(x) Li2O (0 ≤ x ≤ 35) were prepared using the melt quenching technique. All the prepared glass samples are amorphous as confirmed by XRD. The experimental and theoretical densities are found to decrease with increasing Li2O content, and following the same trend, while the molar volume (Vm) has an opposite trend with the concentration of Li2O. The glass transition temperature (Tg) and crystallization temperature (Tc) were found to decrease with increasing of Li2O content except for glass sample with x = 15 mol%, this glass sample exhibit the highest thermal stability. The FTIR of the prepared glasses were investigated all the vibrational modes of prepared glasses. The variation of optical absorption edge, optical band gap (Eg) and Urbach energy (Eu) depend on Li2O content. It is observed that the increase of Li2O content increases the energy gap values and decrease the Urbach energy which is an indication of the increase in structural disorder of glass.The dc and ac conductivity and their related conduction mechanisms of the investigated glasses were analyzed. Activation energies ΔEdc1, ΔEac1, ΔEdc2 and ΔEac2 at low and high temperatures are calculated. It was found the behavior of both ΔEdc and ΔEac are approximatelythe same.
The ac conductivity studies of investigated glasses have been carried out at different concentration of Li2O mol% and the data has been analyzed by using Almond-West power-law[Equation 2.20]
σac = σ(0) + A . ωs
The power-law exponent S is found to decrease with increasing temperature and exhibits lower values in highly modified glasses. The correlated barrier hopping (CBH) seems to be the most interesting model related to the obtained results.
The dielectric parameters ε’ and ε’’ are found to increase with the increase in temperature and their variation with Li2O mol% pass through a maximum at 15 mol% Li2O. These results were discussed using dielectric polarization mechanism of material. The values of the maximum barrier height Wm obtained from Guitine equation were found to increase with increasing of the concentration of Li2O mol% except 15 mol% Li2O glass.
Also, the present work studies the effect of CuO on the structural, optical and electrical properties of (55 – x) P2O5 – 30 Na2O – 15Li2O – (x) CuO [0 ≤ x ≤ 1] glass and glass-ceramic systems. The undoped glass was found to be colorless, bubble-free and transparent while the color of doped glasses changed from light green to dark green with increasing the CuO content. Physical properties of the prepared samples have been studied. The amorphous and crystalline nature of the as-prepared and annealed samples has been confirmed by X-ray diffraction and TEM. Absorbance of the investigated samples was measured in (UV-Vis) range used to evaluate the optical energy gap and Urbach energy, they found to depend on the sample compositions. The value of σdc found to be the same as the value obtained from the impedance study. The grain resistance conductivity mechanism at room temperature was discussed using a Cole-Cole plot. To determine the conduction mechanism, the ac conductivity and its frequency exponent (s) found to have values ranging from 0.671 to 0.916. Consequently, the correlated barrier hopping model is by all accounts the most fascinating model identified with the obtained results. The imaginary part ε” and real part ε’ frequency dependence of dielectric constants were analyzed and discussed using dielectric polarization mechanism of the samples. The estimation of maximum barrier height Wm got from Guitini condition was found to decrease with increasing of CuO content.