>>13709199powder X-Ray is really nifty stuff, because you get flexibility and temporal resolution that you don't really get anywhere else. Want to check out phase transitions at different temperatures? Want to follow reactions in sold-state chemistry? Want to quickly check the crystallinity of your material? powder XRD has you covered.
What powder XRD can't do is completely "solve" crystal structures. You can determine the crystal system, measure the key parameters of the unit cell and compare the obtained reflexes against a database. Then again, you can literally grind up any random rock you find outside and it will give you a reasonable powder x-ray that allows quick identification, even with complex mixtures.
>>13709258Debye-Scherrer is a diffractometer geometry, where you place your powder sample in the middle of a ring of photographic film, it used to be quite common, but since we have good scinitillation x-ray detectors nowadays, most powder x-rays use Bragg Brentano geometry
pic related, it's a Debye-Scherrer camera. The sample goes in the middle, photographic film on the outside, shoot some x-rays into the middle, develop the film and you're done
