X-ray diffraction is a cornerstone technique essential for revealing the atomic and molecular arrangement within crystalline materials. There are two methodologies within X-ray diffraction: Single crystal and powder. Each approach presents unique advantages and applications in the study of crystalline structures.
This article will explore the primary differences between these methodologies, starting with single crystal X-ray diffraction.
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Single Crystal X-Ray Diffraction
Single crystal X-ray diffraction, sometimes referred to as Laue XRD, provides details about the internal lattice and structure of crystalline substances, like unit cell dimensions, bond lengths, angles, and atomic positions. The Laue XRD method leverages the principle of constructive interference of monochromatic X-rays with the crystal when Bragg’s Law is satisfied. You can read more about the Laue Method in our detailed guide.
- Provides Highly Detailed Structural Information: Single crystal XRD offers unparalleled insights into the atomic structure of a crystal down to bond lengths and angles.
- Non-Destructive Technique: The analysis does not alter or damage the sample, allowing repeated measurements or further analysis of the same sample.
- Unsurpassed Precision: This technique offers the ability to determine atomic positions with high precision, often better than a few thousandths of a nanometer.
- Broad Application Range: Besides identifying unknown crystalline substances, XRD can determine unit cell dimensions, quantify mineral amounts, and even measure purity. It can also provide crucial data like thin film properties and texture measurements.
- Sample Size & Quality: The single crystal XRD method requires large crystal sizes and is better performed on single crystal samples rather than polycrystalline.
- Data Collection Time: Acquiring a dataset can take additional time, especially compared to other analysis techniques.
- Complexity in Data Analysis: Without the proper analysis tools, the data requires careful processing, correction, and transformation to generate meaningful results, making this method less accessible to non-specialists.
Powder X-Ray Diffraction
Powder X-ray diffraction (XRD) is a technique used to identify the crystal structure of materials. The process works by directing X-rays at a powdered sample of the material.
As the sample is rotated, a detector picks up the X-rays that are diffracted at specific angles according to the distances between the planes of atoms within the crystal structure. The information collected by the detector is used to create a unique profile of the material, which can help identify its crystalline structure.
- Rapid Identification: Powder XRD provides quick and definite results (often under 20 minutes), which can be crucial when time is of the essence. The entire process, from directing the X-rays to obtaining results, usually takes a few hours.
- Minimal Sample Preparation: The need for relatively little prep makes it user-friendly and resource-efficient. The sample needs only to be powdered to specific dimensions.
- Handles Multi-Component Mixtures: The Powder XRD method can handle samples that consist of multiple components. It can detect and separate the diffraction peaks of different components in a mixture and provide comprehensive structural information.
- Versatile Sample Types: Powder X-ray diffraction can be performed on various samples. These include powders, sintered pellets, or coatings on substrates, making it incredibly versatile in its various applications.
- Requires a Homogeneous Sample: XRD relies on the assumption that each particle in an analyzed sample is identical in composition. This limitation prevents it from being completely accurate when dealing with heterogeneous samples, where mixed materials can have a detection limit as low as approximately 2% of the sample.
- Inefficient Measurement Technique: Due to its working principle, only a small fraction of crystallites in a specimen contribute to the measured diffraction pattern, thus making it inefficient.
- Limited to Reference Patterns: In the Powder XRD method, to identify an unknown substance, the diffraction pattern must match one of the existing reference patterns, potentially limiting its applications.
- Particle Size Limitations: Optimal results with XRD are obtained only when the sample particles are less than 10 micrometers in size. This limits the type and condition of samples that can be effectively analyzed.
- Peak Overlay Occurrence: For high-angle reflections, peak overlay may occur. This peak overlay may worsen even further as the angle increases.
Learn More From Pulstec
Pulstec is a leading manufacturer of electronic equipment, including the s-Laue Single Crystal Orientation System. This new and innovative system is capable of acquiring images of single crystal materials in as little as 60 seconds. It can be used to measure principle plane orientation, check and adjust cutting orientation, evaluate crystallinity, and analyze processing-related crystal growth.