Investigation of ion dynamics in mixed network former glasses

Abstract

The work of this thesis is mainly based on the study of structure and ion dynamics of several new ion conducting glasses and to correlate the macroscopic ion transport properties to the glass network structure and the microscopic lengths. The organization of the thesis is as follows Chapter 1 of this thesis deals with the literature review in the field of glasses. A brief introduction to glasses is presented and their exotic features are discussed. The network structures of different type of glasses are briefly discussed. Several theoretical models and concepts used to explain and understand the ion dynamics are pointed out. Finally the scope of the thesis is presented. In chapter 2 a brief description of the preparation technique of glasses and glassnanocomposites and various experimental methods used to characterize them are presented. In the initial part of the chapter the structural characterization such as density, x-ray diffraction (XRD), differential scanning calorimetry (DSC), transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM) and Fourier transform infrared (FTIR) spectroscopy techniques are discussed. In the later part, electrical characterization techniques used to study the ion dynamics are presented. In Chapter 3 the structural and electrical properties of xAgI-(1-x)(0.3Ag2O- 0.7(0.5SeO2-0.5MoO3)) glasses have been investigated. The structural characterizations of these glasses have been carried out using XRD, FTIR spectroscopy etc. and the thermal study has been done using Differential Scanning Calorimeter. The Ag+ ion dynamics in the glasses has been investigated in a broad frequency range from 10Hz – 2MHz and in wide temperature range. The dc conductivity and the microscopic lengths obtained from the linear response theory have been correlated to the glass network structure. Chapter 4 deals with the study of mixed former effect and dynamics of Ag+ ions of xAgI-(1-x)(0.3Ag2O-0.7(ySeO2-(1-y)MoO3)) glasses. The glass formation has been confirmed using XRD. The thermodynamic properties of these glasses have been explored using DSC. The modification of the glass network structure has been analyzed using deconvolution of the FTIR spectra. The ionic conductivity of these glasses has been compared to that of the undoped silver selenomolybdate glasses. The study of relaxation dynamics in these glasses has been performed in the framework of the conductivity and the electric modulus formalism. The characteristic lengths obtained from the conductivity and dielectric spectra have been correlated to the modification of the glass network structure. In chapter 5 the study of mixed former effect and ion dynamics in silver ion conducting mixed network former glasses of composition yAg2O-(1-y)(xSeO2-(1-y))TeO2 are presented in wide composition and temperature ranges. The glass network structures and structural modification depending on composition has been investigated using FTIR spectroscopy. The ion dynamics in these mixed former glasses has been studied using the conductivity formalism as a function of frequency and temperature. The correlation of ion transport properties to the microscopic length scales and the glass network structure has been established. In chapter 6 the Ag+ ion dynamics in xAgI-(1-x)(yAg2O-(1-y)(0.5SeO2-O.5TeO2)) mixed network former glasses for different modifier content is presented. The thermal properties of these glasses have been studied using DSC. The relative concentrations of different network structural units have been determined from the de-convolution of the FTIR spectra. The ac conductivity has been investigated taking the contribution of the electrode-sample interface. The length scales of ion dynamics, such as characteristic mean square displacement and spatial extent of sub-diffusive motion of silver ions have been determined from the ac conductivity and dielectric spectra respectively in the framework of linear response theory. A direct correlation between the ion dynamics and the characteristic length scales and the glass network structure has been established for different compositions of the selenium-tellurite glasses. In Chapter 7 the summary of the thesis is presented. The possible future research in continuation of this work is also highlighted.Research was carried out under the supervision of Prof. Aswini Ghosh of Solid State Division under SPS [School of Physical Sciences]Research was conducted under DST grant and IACS fellowshi