Powder X-ray Diffraction
A rapid, non-destructive analytical technique used to study polycrystalline materials.
PXRD is a fast, non-destructive analytical technique used for the characterisation of crystalline materials (those which have a degree of order to their structure). When a crystalline sample is exposed to an X-ray beam of known wavelength, a unique diffraction pattern is generated. If more than one material (or phase) is present, the diffraction patterns for each material overlaps. By identifying each pattern in the diffractogram, individual materials (or phases) can be recognised and quantified.
Through interpretation of diffraction patterns, PXRD analysis allows:
- Identification of crystalline phases
- Measurement of crystallite/crystal domain size within discrete crystalline phases (always best to compare with microscopy techniques such as SEM)
- Calculation of unit cell dimensions through pattern indexing
- Phase quantification using simple profile fitting, LeBail, Pawley or Rietveld refinements
In addition to standard experiments, our PXRD facility can run samples under inert atmosphere (for air-sensitive samples) and under different gases and vapours to monitor the stability of materials under different conditions.
PXRD can provide a comprehensive picture of the solid state properties of any crystalline material. Get in touch to discuss contract work, or for one-off measurements.
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Powder X-ray Diffraction (PXRD) is a powerful technique to analyse single and multi-phase polycrystalline materials. It can be used on a wide range of solid-state materials, including alloys, cements, refractories, pharmaceuticals, nanomaterials, glasses, and more.
Within Newcastle University, we use PXRD for applications including:
- Phase identification – comparing the measured diffraction peaks to a database of known patterns, allowing the identification of the phase(s) within a single sample
- Phase quantification – if calibration samples are available, the quantity and relative distribution of phases within polycrystalline samples can be accurately determined. Alternatively, combining PXRD with Scanning Electron Microscopy analysis can be used to determine relative phase distribution
- Crystallite size analysis – the average crystallite size within a sample can be identified using the Scherrer equation. Through comparison with Electron Microscopy, the morphology and particle size can also be determined
Determination of phase purity
To determine accurate structure-property relationships in a material, it is crucial to ensure that the material is pure. Powder diffraction gives a direct representation of the bulk sample, with the observed pattern derived from all the crystalline components within the material.
In this case study, we will look at the determination bulk purity of a porous material known as a metal-organic framework. We will compare the powder diffraction pattern to the single crystal structure, using a whole pattern fitting method known as a LeBail fit.
More on Determination of Phase Purity.
Phase identification
When samples are chemically identical, but possess different crystalline phases (or polymorphs), powder X-ray diffraction (PXRD) can rapidly distinguish between different phases of the same chemical composition. This is important within pharmaceuticals as PXRD can determine the difference between an active and a non-active polymorph in minutes. PXRD can also be used to identify minerals (such as quartz and cristobalite – both SiO2), unreacted species, corrosion products amongst many other applications, where a solid crystalline form required identification.
In this case study, we will look at the Phase Identification from a research sample formed from a high temperature reaction of apatite-wollastonite glass mixture.
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