Aside from making sure the powder is as fine as possible, one of the most important things you can do is make sure the top surface of your slide is as flat and even as possible. Then, when mounting it in the diffractometer, make sure it is perfectly centred and that any beam masks you're using are of the correct size to match your slide. If you're new to X-ray diffraction, I suggest finding someone more experienced to show you their methods for doing these things - good practice varies widely from setup to setup, and experience is always valuable!

Properly preparing your powder and your slide will give you better quality data. So will making sure the slits fitted to the machine are appropriate to the source and sample. In the end though, there will always be a need to collect over long periods of time to get the best quality data.

Aside from making sure the powder is as fine as possible, one of the most important things you can do is make sure the top surface of your slide is as flat and even as possible. Then, when mounting it in the diffractometer, make sure it is perfectly centred and that any beam masks you're using are of the correct size to match your slide. If you're new to X-ray diffraction, I suggest finding someone more experienced to show you their methods for doing these things - good practice varies widely from setup to setup, and experience is always valuable!

Properly preparing your powder and your slide will give you better quality data. So will making sure the slits fitted to the machine are appropriate to the source and sample. In the end though, there will always be a need to collect over long periods of time to get the best quality data.

After you have followed Philip's advice, try the following.

If the powder is not too affected by preferential orientation (flaky crystals) a reliable and fast method consists of the following:

- diperse a homogeneous and fairly thick layer (approx 0.2 - 0.5 mm) of powder on the desired area (approx 1 x 1.5cm) of a glass slide by means of a needle mounted on a handle. This way you obtain a sort of a fluffy layer of powder.

- Dispense a few drops of solvent which does not react with your powder (acetone, alcohol, etc. or even distilled water) by means of a very fine pipette. Make sure all the powder is thoroughly wetted and the surface tension of the liquid keeps the powder nicely within the area designated without wetting the rest of the slide where there is no powder.

- Leave to evaporate without disturbing on an absolutely flat surface. The powder will adhere to the surface quite nicely and you'll have to scrape it off with a blade to recover it (if needed).

- When mounting the slide on the goniometer, compensate the thickness of the layer of powder (by then reduced to some 0.05mm or less) with some thin sticky tape or gummed paper (useful also to label the slide).

If you have started with a well prepared powder (you should hardly feel the grains between thumb and forefinger), the preparation of the slide will not take more than 3-5 minutes, plus the time it takes to evaporate the solvent, of course.

Good luck!

On a glass slide, apply a piece of double sided Scotch tape (1.5 cm by 1.5 cm). Spread some powder uniformly on the tape, and use another glass slide to press the powder so that powder adheres to the tape. The Scotch tape generates very small background of X-ray scattering.

http://www.staples.com/Scotch-Double-Sided-Removable-Tape-with-Dispenser-3-4-inch-x-400/product_383534?cid=PS:GooglePLAs:383534&srccode=cii_17588969&cpncode=27-270898207-2

For what it's worth, my preferred method for large powder samples involves an aluminium plate with a square cutout through its whole thickness. Tape a glass microscope slide to the top and fill from underneath, packing tightly against the glass slide. Next, tape another slide to the bottom, turn the sandwich over and (carefully!) remove the top slide. The result, when carried out carefully, is a slide with tightly-packed powder, exactly flush with the top of the aluminium plate.