Editorial Feature

X-Ray Diffraction vs. X-Ray Fluorescence

X-Ray-based analytical techniques, such as X-Ray diffraction (XRD), X-Ray fluorescence (XRF) spectrometry, X-Ray absorption spectroscopy, X-Ray photoelectron spectroscopy, and X-Ray reflectometry, are invaluable in material science for analyzing the composition and structure of materials.1

X-Ray Diffraction vs. X-Ray Fluorescence

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These techniques rely on interactions between X-Ray photons, produced by electron transitions within atoms and specimens, which lead to absorption, scattering, or fluorescence.2 These interactions with core electrons form the basis of XRD and XRF studies.

Although both XRD and XRF originated over 100 years ago, they have become widely used in industrial and research settings in the past 50 years.

XRD provides structural insights and estimations of phase composition through diffraction patterns, while XRF determines elemental composition by analyzing the emitted X-Ray wavelengths.2 Both methods offer precise qualitative and quantitative data, making them essential in material characterization. Together, they enable a comprehensive analysis of material samples.

Fundamental Principles of XRD vs XRF

All substances are composed of individual atoms, and nearly all have some level of periodicity in the arrangement of these atoms. When X-Rays interact with a sample, they scatter and create a diffraction pattern.

According to Bragg’s law, the diffraction pattern depends on the X-Ray wavelength and the distance between atomic planes. By measuring diffraction angles under a predetermined monochromatic wavelength, scientists can calculate distances between atomic layers, helping them understand the material's structure and phase composition.3

XRF spectroscopy relies on the interaction between high-energy X-Rays and the atoms in a sample, similar to XRD. When materials are exposed to high-energy, short-wavelength X-Rays, the atoms can become ionized if the radiation dislodges a tightly held inner electron.4

This makes the atom unstable, prompting an outer electron to fill the vacancy. This transition releases energy in the form of fluorescent radiation, which has a lower energy than the incident X-Rays.4

The energy of the emitted photons is characteristic of the specific electron transitions within an element, enabling detection and quantification of elements in the sample.

Key Differences in Function

XRF identifies the elemental composition of a sample by measuring the fluorescent X-Rays emitted when the sample is excited by a primary X-Ray source. The energy released in the form of X-Rays is unique to each element, making XRF a powerful tool for detecting elemental components.56 However, XRF does not provide information on the structural arrangement of these elements within the sample.

In contrast, X-Ray diffraction (XRD) focuses on analyzing a material's crystalline structure. By examining the diffraction pattern produced when X-Rays scatter off the atomic planes of a crystal, XRD reveals the material's atomic arrangement and phase composition.

XRD can identify and quantify different phases within a mixture, evaluate amorphous content, solve crystal structures, and analyze crystal structure changes due to temperature, pressure, or doping.6 Thus, while XRF provides detailed elemental analysis, XRD offers insights into the structural organization and phase relationships of the elements in the sample.

Applications: XRD vs XRF

XRD is widely used in both research and industry for its numerous applications. By comparing XRD patterns with a library of known patterns, it can identify single or multiple phases in unknown samples, making it valuable for identifying mineral phases, quantifying phases in mixtures, and assessing material crystallography.7

XRD is also essential for surface and thin film analysis, texture analysis, and evaluating amorphous content. It plays a critical role in quality control and assurance, particularly in delivering safe polymeric materials, ensuring the quality of crystalline pharmaceutical samples, and identifying toxic elements in mineralogical samples. This versatility underscores XRD's broad utility in material science and related fields.8

Although XRD identifies minerals and phases, it does not reveal the chemistry, making XRF valuable for its precise elemental analysis across various industries.7 In the metals and alloys industry, XRF ensures good quality control and consistency by accurately determining chemical composition.9

Environmental applications of XRF include soil surveys, water and air pollution tests, and more. It is also crucial in cement manufacturing, metallurgy, mining, petroleum and polymer industry, paints and chemicals manufacturing, and forensics, providing both qualitative and quantitative analysis with rapid and reliable results.9

Handheld XRF analyzers offer immediate elemental analysis in the field, while lab-based systems deliver detailed process and quality control.

In the medical sector, XRF contributes significantly to diagnostics and research by detecting high levels of specific chemicals in various parts of the human body, aiding in the identification of potential illnesses.9

XRF is also used for in vivo and in situ measurements of malignant cells and tissue sampling. It also helps determine levels of harmful radiation, making it a valuable tool in medical diagnostics and assessing environmental health impacts on human physiology.

Both XRF and XRD offer comprehensive material analysis. For example, XRF can measure the total concentration of elements like calcium or iron, while XRD can determine the specific phases these elements form, such as CaO, CaCO₃, or various iron oxides.10 Combining these techniques provides a more complete characterization of chemical samples.

Advantages and Limitations

XRD

XRD offers several advantages, including rapid material identification, minimal sample preparation, and access to extensive databases of known crystalline structures.11 The technique is efficient and accurate, requiring only small sample quantities ground to less than 10 micrometers. It provides clear results by measuring internal stress, crystalline size and shape, and atomic layer spacings.

However, XRD cannot identify amorphous materials directly and needs single-phase, homogeneous samples for accurate analysis.6 While effective for large crystalline structures, XRD may miss trace elements and has a detection limit of 2 % for mixed materials. Despite these limitations, XRD remains a valuable and widely available tool for material analysis.

XRF

XRF offers fast, non-destructive analysis with high accuracy and a wide range of element detection, making it a valuable tool for both solids and liquids. It requires minimal sample preparation and has low running costs, with instruments that do not need daily recalibration. It can also provide quantitative analysis from ppm to 100 % and deliver precise and accurate results by measuring the consistency of repeated values.12

However, XRF has limitations, such as lower detectability for light elements and sensitivity to environmental factors, matrix effects, and superposition effects. Additionally, the technique requires specific sample volumes for optimal performance and reference standards similar to the test samples for the highest accuracy.6

Summary and Future Outlooks

XRD and XRF are essential techniques for material analysis, each offering unique strengths that complement the other.

XRD excels in revealing the structural and phase composition of crystalline materials, making it ideal for identifying and quantifying mineral phases and assessing crystallography.

Conversely, XRF provides rapid, non-destructive elemental analysis, delivering precise quantitative data across a wide range of elements with minimal sample preparation. Its versatility spans various industries, including metals, environmental, and medical fields. However, XRF's sensitivity to light elements and environmental factors requires careful calibration and sample considerations.

The integration of XRD and XRF in modern systems enhances their utility by enabling comprehensive material characterization from a single sample introduction. This integration reduces costs and streamlines the analysis process, offering a holistic view of both elemental composition and structural organization.2

Modern systems allow both techniques to be performed on the same instrument, simplifying the process with combined elemental and phase results. Together, XRD and XRF empower scientists and engineers to advance material science and various industrial applications.

More from AZoOptics: The Role of Mass Spectrometry in Protein Analysis

References and Further Reading

  1. Covalent Metrology (2024). X-Ray Analysis Techniques. [Online] Covalent Metrology. Available at: https://covalentmetrology.com/analytical-services/X-Ray-analysis-techniques/
  2. Jenkins, R. (2000). X-Ray techniques: Overview. [Online] Encyclopedia of analytical chemistry. Available at: https://analyticalscience.wiley.com/do/10.1002/sepspec.10152education/full/i4cc1d739cc8a1bc85c7f13f840c4e021.pdf
  3. Warren, BE. (1990). X-Ray Diffraction. Courier Corporation. ISBN, 0486663175, 9780486663173
  4. Carleton College. (2007). X-Ray fluorescence. [Online] Geochemical Instrumentation and Analysis. Available at: https://serc.carleton.edu/research_education/geochemsheets/techniques/XRF.html
  5. Igwebike-Ossi, CD. (2017). X-Ray techniques. Failure analysis and prevention. doi.org/10.5772/intechopen.72447
  6. Quantum Analytics (2021). XRD or XRF? Deciding Which Technique is Best for Material Characterization? [Online] Quantum Analytics. Available at: https://www.lqa.com/wp-content/uploads/2021/04/XRD-or-XRF-Best-for-Material-Characterization.pdf
  7. Yerly, R. (2015). Better together: XRD and XRF. [Online] Thermo Fisher Scientific. Available at: https://www.thermofisher.com/blog/mining/better-together-xrf-and-xrd/
  8. XRF Scientific. (2018). Outlining XRF Applications. [Online]. XRF Scientific. Available at: https://www.xrfscientific.com/outlining-xrf-applications/
  9. Thermo Fisher Scientific. (2006). X-Ray Diffraction Applications. [Online] Thermo Fisher Scientific. Available at: https://www.thermofisher.com/in/en/home/industrial/spectroscopy-elemental-isotope-analysis/oes-xrd-xrf-analysis/X-Ray-diffraction/applications.html
  10. Mohamed, M., Yusup, S., Maitra, S. (2012). Decomposition study of calcium carbonate in cockle shell. Journal of Engineering Science and Technology. https://jestec.taylors.edu.my/Vol%207%20Issue%201%20February%2012/Vol_7_1_001_010_SUZANA%20YOUSUF.pdf
  11. Dutrow, BL., Clark, CM. (2018). X-Ray Powder Diffraction [Online] Carleton College. Available at: https://serc.carleton.edu/msu_nanotech/methods/XRD.html
  12. Li, F., Ge, L., Tang, Z., Chen, Y., Wang, J. (2020). Recent developments on XRF spectra evaluation. Applied Spectroscopy Reviews.​​​​​​ doi.org/10.1080/05704928.2019.1580715

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