Powder Diffraction: 101

Powder diffraction at the APS:

The APS operates two dedicated powder diffraction beamlines. Find more information on the Structural Science group website or this overview poster on powder diffraction at the APS

What is X-ray diffraction?

Powder X-ray diffraction is a versatile, non-destructive technique that reveals detailed information about the chemical composition and crystallographic structure of natural and manufactured materials. Experimental preparation is minimal and only a small amount of powder sample is required. The distinctive diffraction pattern 'fingerprint' of crystalline materials can be used to identity and quantify different components in a multi-phase mixture, provide information about size and strain distributions within a powder sample, or to obtain a detailed model of the material's atomic structure. Powder X-ray diffraction method is also readily performed with non-ambient sample environments, allowing crystallographic changes and phase transitions to be observed as a function of temperature, pressure or other parameter. High-resolution measurements preformed at the APS afford a level of detail and sensitivity unmatched by commercial lab based powder diffractometers.

Research problems that this technique can address may include:

• Structural studies of crystalline materials
• Drug design and polymorph discovery for the pharmaceutical industry
• Development of new catalysis and battery materials for energy applications
• Quantification of mixed phase mineral and soil samples
• Novel complex oxides: structure-property relationships and phase transitions
• Grain size and stress studies of advanced metal alloys

How the technique works:

X-rays have wavelengths comparable to the distance between atoms. When a crystalline sample is illuminated with X-rays, the X-rays are scattered (diffracted) at specific angles with various strengths. The random arrangement of grains within a powder sample enables powder X-ray diffraction to measure all the these diffraction peaks in a single scan. Detectors are used to measure this diffraction pattern (typically a plot of angle vs intensity), which is then analyzed to reveal information about the crystalline phases present in a sample. For the high-resolution powder XRD measurements at the APS, sample powders are loaded in small (~1 mm) capillary tubes, and data is collected in a transmission geometry with scan times ranging from a few minutes to hours.

Why is it useful?

Many of the most interesting materials being studied today are not available in single-crystal form during the critical period following the initial discovery. However, it is precisely during this initial phase that detailed structural information is most critically needed. In addition, many phase transformations chemical processes destroy single crystals, restricting materials available to powders. Furthermore, powder diffraction studies of increasingly complex modern materials may be limited by the detail of available data. The high-resolution powder diffraction beamline (11-BM-B) at the APS, which offers the highest resolution in the Americas, exists to remove this research obstacle and to provide the structural information essential for defining the future synthetic approaches required in optimizing properties of these new materials