Recap provided by Aya Takase
Thank you to everyone who joined us for Episode 3 of MiniFlex Office Hour! As always, our XRD expert, Akhilesh Tripath, shared valuable insights and answered practical questions from MiniFlex users around the world. Below is a quick recap of the key topics we covered.
You can watch the full recording here. If you’re new to MiniFlex, it’s a benchtop X-ray diffractometer that researchers have trusted since 1973.
Here are some of the key questions Akhilesh answered during the session:
Yes. If your sample sits higher than it should, it causes all peaks to shift systematically to the right (higher 2θ values). To prevent this:
For plate-shaped bulk samples, use sample holders with wells that match your sample’s height, or opt for bulk sample holders, as demonstrated in this video. For thin samples on glass slides, a shim of matching thickness can bring the glass down to the correct depth when used with a spring holder.
Zero background holders are another excellent choice, particularly when dealing with small powder quantities. These reduce background noise and come in various types with different diameters and depth combinations for the well. Choosing the right holder often depends on the sample’s amount and size.
High background can be sample-dependent, but it can be minimized by engaging the knife edge. The knife edge acts as a barrier to prevent stray X-rays from directly hitting the detector at low angles. It’s easy to engage or disengage with a physical click.
Additionally, avoid using sample holders made of materials like glass, which contribute to the background. A narrower slit also helps, and using the variable slit mode on the MiniFlex is very effective. It adjusts automatically, narrowing at low angles and widening at higher ones, to strike a balance between reducing background and maintaining peak intensity.
The MiniFlex is available in two power versions: 600 W and 300 W. A typical power setting for the 600 W model is 40 kV and 15 mA. These settings are fixed once the unit is purchased and can’t be changed during operation.
There's also a low-power "rest mode" (20 kV, 2 mA) that helps extend the instrument’s life during idle periods.
The 600 W version provides higher X-ray intensity and thus requires shorter data collection times, typically about half that of the 300 W version. If you are doing quick phase identifications and have budget constraints, the 300 W system could suffice.
However, if budget isn’t a concern and better performance is desired, the 600 W version is the recommended choice.
The MiniFlex measures roughly 620 mm (W) × 722 mm (H) × 460 mm (D). That’s a bit larger than a microwave, yet smaller than a typical oven.
You should plan for an additional 1 to 2 feet (about 30-60 cm) of clearance around the unit for comfortable operation and maintenance, as well as space for the computer setup. Overall, the MiniFlex requires minimal lab space.
The most common mistake is incorrect sample height. Ensure that the powder fills the well to the brim and forms a flat surface. A lumpy or uneven sample can lead to errors, such as peak shifting or broadening.
Another common issue is inadequate grinding and packing. Samples should be finely ground, ideally to 10 microns or less, for best results. For samples safe to touch, a simple finger test helps: if it feels like talcum powder and not gritty like sand, it’s fine enough. Proper packing ensures consistent sample density and avoids overestimation of certain phases caused by preferred crystal orientations.
Preferred orientation happens when particles naturally align in a specific direction, especially in flat or fibrous materials. No amount of grinding removes the intrinsic shape, but you can minimize its effects using a few techniques.
One option is using a spinning capillary, which helps expose different crystal faces. You can also use transmission sample holders instead of reflection mode to access more orientations. Slurries made with ethanol can help randomize particle alignment as they dry.
Another method is the “stick in the mud” approach—using a layer of grease with no X-ray signature to hold loosely deposited particles in random directions. Advanced methods like backloading or sideloading help, too, but the sample preparation with these techniques are tricky and requires practice.
Note that even with good prep, preferred orientation may persist. Analysis methods like the WPPF (whole powder pattern fitting) and Rietveld methods offer corrections using the March function, allowing you to model and adjust for overrepresented peaks using known HKL indices and help obtain accurate quantitative analysis results.
We’ll be back every month with more questions, tips, and insights from Akhilesh. If you use MiniFlex or are curious about benchtop XRD, we hope you’ll join us live next time!
The live event information is posted on our LinkedIn event page.
Got questions in the meantime? Drop your question in the comment section of the most recent episode. Akhilesh will answer them, or we might answer it live during the next office hour.