Powder Diffraction Method Analysis

Fig shows 3.13 powder diffarction pattern (it shows diffraction lines and holes for incident and transmitted beam)

If a powdered specimen is used,instead of a single crystal,then there is no need to rotate the specimen,because there will always besome crystal at an orientation for which diffraction is legitimate.Here a monochromatic X ray beam is incident on a powdered or polycrystalline sample.This method is use ful for samples that are difficult to obtain in single crystal form.

The powder method is used to determine the value of the lattice parameters accurately.Lattice parameters are the magnitudes of the unit vectors a,b and c which define the unit cell for the crystal.

It is not applicable to grains larger than about 0.1 to 0.2 μm, which precludes those observed in most metallographic and ceramographic microstructures.It is important to realize that the Scherrer formula provides a lower bound on the particle size. The reason for this is that a diversity of factors can contribute to the width of a diffraction peak besides influential effects and crystallite size; the most important of these are customarily inhomogeneous strain and crystal lattice imperfections. The following sources of peak broadening are listed in reference[18]. dislocations, stacking faults, twinning, microstresses, grain boundaries, sub-boundaries, coherency strain, chemical heterogeneities, and crystallite smallness. If all of these other contributions to the peak width were zero, then the peak width would be determined solely by the crystallite size and the Scherrer formula would apply. If the other contributions to the width are non-zero, then the crystallite size can be larger than that prophesied by the Scherrer formula, with the "extra" peak width coming from the other factors. The concept of crystallinity can be used to communally describe the effect of crystal size and imperfections on peak

3.5.2.1 Working of Ellipsometry

The following different components collaborate to compose the spectroscopic ellipsometry data,

• Source of light

• Polarization generatoe

• Analyzer

• Sample and