Sample holder & stage
Most diffractometers are supplied with several kinds of sample holders for different types of specimens such as powders, bulk samples and thin films. The best results are obtained with rotating sample holders which considerably improve the measurement statistics, but they are not available for all machines. The most severe error during sample preparation is to fill the sample holder too high or low. Both result in a significant shift of peak positions which can make the interpretation difficult.
Image taken from the NTU XRD site sample holder page
The sample stage keeps the specimen fixed in the right position during the experiment. The sample holder is mounted on the sample stage which keeps the sample aligned in the beam and controls the movement of the sample.
Image taken from the NTU XRD site sample stage page