Powder X-ray Diffraction
A rapid, non-destructive analytical technique used to study polycrystalline materials.
PXRD is a rapid, non-destructive analytical technique used for the characterisation of crystalline materials, i.e. 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, then the diffraction patterns for each material is overlapped. Through identification of each pattern within the diffractogram, individual materials (or phases) can be identified 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 has the capability to 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. If you are interested in working with us, please get in touch to discuss any potential contract work, or for one-off measurements.
Our services
Powder X-ray Diffraction (PXRD) is a powerful rapid analytical technique for the study of single and multi-phase polycrystalline materials. PXRD can be used to characterise a wide range of solid-state materials, including alloys, cements, refractories, pharmaceuticals, nanomaterials and glasses, to name a few.
Within Newcastle University, we utilise 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 – providing 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 – Utilising the Scherrer equation, the average crystallite size within a sample can be determined. Through comparison with Electron Microscopy, the morphology and particle size can also be determined
Determination of phase purity
In order to determine accurate structure-property relationships in a material, it is crucial to ensure that the material being studied 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.
Within 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.
Read further, on Determination of Phase Purity.
Phase identification
When samples are chemically identical, but possess different crystalline phases (or polymorphs), powder X-ray diffraction (PXRD) is a key analytical tool as it can rapidly distinguish between different phases of the same chemical composition. This is especially important within pharmaceuticals as PXRD can determine the difference between an active and a non-active polymorph in minutes. In addition, PXRD, can be used in the identification of minerals (such as quartz and cristobalite – both SiO2), unreacted species, corrosion products amongst many other applications, where a solid crystalline form required identification.
Within this case study, we will look at the Phase Identification within a research sample formed from a high temperature reaction of apatite-wollastonite glass mixture, provided by a user at Newcastle University.
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