**Abstract**

In this chapter a systematic investigation of impact of mechanical activation on structural, microstructural, thermal and optical properties of MgO – TiO2 nanocrystalline composite system, synthesized via high energy ball milling techniques. Williamson-Hall (W-H) plot method was employed to understand the signature of the broadening in the XRD peaks and for the estimation of crystallite size of MgO – TiO2 nanocrystalline composite system. It revealed that the peak broadening is not only due to reduced coherently diffracting domain size but also due to a significant strain distribution. The calculated strain was 9.01× 10−3 and the average crystallite sizes were 40–60 nm for 35 hours (hrs) milled powder and this result is very much consistent with transmission electron microscopy (TEM) analysis. The SAED ring pattern indicates that the phase of Mg2TiO4 - nanoparticles was polycrystalline in structure and the distance between crystalline planes was consistent with the standard pattern for a spinel Mg2TiO4 crystal structure. To analyze the lattice fringes for the 35 hrs milled samples high resolution-TEM (HR-TEM) study was carried out and the result revealed that the each particle has single crystalline structure. Morphological studies were carried out by using SEM analysis. The thermal decomposition behavior of the milled powders was examined by a thermogravimetric analyzer (TGA) in argon atmosphere. Also, MTO nanoparticles showed a strong absorption at ~356 nm and the band gap values ranged between 3.26-3.78 eV with an increase of milling time from 0 to 35 hr. The mechanically derived MTO nanoparticles showed promising optical properties which are suitable for commercial optoelectronic applications.

**Keywords:** high energy ball milling, MgO – TiO2 composite system, W-H method, microstructure, TEM and HR- TEM, DSC-TGA analysis, optical studies
