High-Resolution Powder Diffraction Using a Transmission Geometry Method

Table of Content

Transmission Geometry Method
Advantages of Transmission Geometry Method
Example

Transmission Geometry Method

Although the transmission geometry method is not widespread among the crystallography community, it is ideal for powder sample analysis.

The focusing Ge(111) monochromator in combination with a STOE STADI P powder diffractometer delivers pure Kα1 radiation to obtain the maximum possible resolution in 2Θ (FWHM < 0.03°) (Figure 1).

Figure 1. Sketch of a STOE STADI P in Transmission / Debye-Scherrer geometry

Advantages of Transmission Geometry Method

Reliable intensities can be obtained from the transmission geometry over the full 2Θ scale. Height displacement does not have an impact on transmission geometry data (Figure 2).

Figure 2. Height displacement in reflection mode yields a zero shift in the pattern.

The distracting effects of preferred orientation virtually have no effect on the samples quantified in a capillary. Figure 3 shows the plane crystallites in a capillary, and Figure 4 depicts the same material pressed in a reflection sample holder.

The preferred orientation has less effect on the pattern yielded by the statistic deviation of the crystallites in the capillary when compared to the periodic stacking sequence of the planes in the reflection setup.

Figure 3. Plane crystallites in a capillary

Figure 4. Plane crystallites pressed in a reflection sample holder

It is possible to measure even the smallest sample quantities (micro sampling) when prepared between two foils (Figure 5). With transmission geometry, diffraction measurements can be performed at the lowest 2Θ angles.

Figure 5. Transmission sample holder

The beam path in reflection and Transmission geometry is depicted in Figure 6. In the reflection geometry, the unaffected beam leads to false intensities up to 10° 2Θ!.

Figure 6. Comparison of the beam path in reflection (above) and Transmission geometry (below)

Example

Figure 7 presents the application of transmission geometry for low angle measurement of a Zeolite by means of a STADI P with Cu Kα1 radiation. Figure 8 is the magnified image of Figure 7, depicting the remaining hump of the main beam from an added measurement using an empty sample holder.

Figure 7. First two degrees of a low angle measurement of a Zeolite using a Stadi P with Cu Kα1-radiation in Transmission geometry                                        Figure 8. Magnification of picture 7 showing the remaining hump of the primary beam from an added measurement with an empty sample holder

 

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This information has been sourced, reviewed and adapted from materials provided by STOE.

For more information on this source, please visit STOE.

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