6) Xray Spectroscopy

Systems of higher symmetry have ____ peak multiplicity

higher

peak multiplicity of cubic systems

6

peak multiplicity of tetragonal systems

4 and 2

peak multiplicity orthorhombic systems

2, get three different peaks

Why does symmetry affect peak multiplicity

if lattice parameter is the same in more directions then plane spacing in those directions will the same; if the lattice parameter is different then reflections along one axis will be slightly different than along the others

What can affect peak intensity

atomic positions; temperature (positional disorder due to thermal vibrations); site occupancy; texture/preferred orientation; volume fraction of desired phase

How is peak intensity affected by phase fraction

less phase = smaller peaks; small peaks of secondary phases can be lost to background

What are the detection limits and what do they depend on

0.5-10% for powder diffraction; data quality (background noise); density; atomic number; crystal structure

What are the three main contributions to the formulism of peak intensity

experimental setup; phase chemistry (unit cell volume, multiplicity, structure factor); specimen (absorption, volume fraction)

What is the form factor, f

describes the fraction of scattering intensity that is observed with increasing angle; at the centre all e scatter in phase so f = Z; as angle increases e start to destructively interfere reducing f; the larger Z (more e) the faster it falls away