Broadening of the X-ray diffraction peaks in nano-crystalline materials mainly attributed to the following factors:
• Instrumental Broadening
• Crystallite Size Broadening
• Strain Broadening
If breadth consistent for each peak then assured broadening due to crystallite size. Crystallite size is a measure of the size of coherently diffracting domains. The crystallite size of the particles is not generally the same as the particle size due to the formation of polycrystalline aggregates. Lattice strain is a measure of the distribution of lattice constants arising from crystal imperfections, such as lattice dislocations. Other sources of strain include the grain boundary triple junction, contact or sinter stresses, stacking faults and coherency stresses.
So why those peaks sharpen remarkably as the material is heated?