Lattice Parameter Measurements
Lattice parameter measurements are used in many situations to characterize materials. For example, knowledge of the lattice parameters can provide information on the thermal properties of a material, an indirect method to determine the composition in a solid solution, a measure of the strain state, or an analysis of the defect structure. Therefore, it is important to measure the lattice parameter with the highest precision. Fortunately, X-ray diffraction can provide such information to an accuracy of several significant figures if care is taken during the data collection and subsequent analysis.
Two common methods are in use to compute the lattice parameters. If crystallographic information about the crystal structure is incomplete, then a least squares method is commonly used. This method takes into account the systematic errors caused by misalignment and sample placement. If more complete information is known about the crystal structure, then a Rietveld refinement is commonly used. This method is a whole pattern fitting procedure utilizing all of the diffraction peaks and their shapes.
Among the common uses of precision lattice parameters are:
• Material synthesis
• Analysis of solid solutions
• Thermal expansion
• Strain/stress determination
• Misfit strains
• Zeolite framework composition