Basic requirements for the XRD sample preparation
The quality of the collected data cannot be superior to the quality of the sample and to the quality of its preparation and deposition.

That is:

It has absolutely no meaning to lose time of data affected by errors arbitrarily introduced by the poor care taken in sample preparation.


Obviously, depending on the final goal of the analysis (phase identification, polyphasic mixture qualitative and quantitative analyses, indexing, cell refinement, structural determination, etc.) the necessary level of “care” can vary and the time and costs of sample preparation and data collection can be greatly reduced.

The optimal condition making a sample “suitable” for diffraction analysis is that its diffraction data are reproducible on varying the preparation method.

For example, the I/Ic or RIR for the quantitative analyses are estimated through statistical analysis of different sampling and measurements.

The majority of the materials examined by XRD initially appears in a “non-optimal” aggregation state (rocks, minerals, lacquers, conglomerates, tablets, etc.) and need to be ground to obtain a fine powder.


Common case: Mortar and pestle (glass for soft materials, agate for hard materials, BN for extremely hard species.
Or: Mechanical millers with agate, metal alloy, tungsten carbide beads.

Grinding times: seconds to minutes.

Caution! A prolonged grinding may create a large specific surface (with surface reconstruction or transformation), merging of particles, loss of crystallinity or even chemical reactions (phase transitions, desolvation, polymerizations).


Other tricks:

  • to make a plastic material fragile, one can perform the grinding or milling within a liquid nitrogen environment.
  • repeated heating (10-30 min) of the sample at about 1/3 of its m.p. (in K) may eliminate defects.
  • usage of a chemically inert liquid to avoid clustering of soft particles.
  • sieving between 25 - 75 µm, also under pressure or within a flux of an inert liquid.

    Caution: Avoid contamination by the mortar or by the miller.
    Caution:Problems with ductile materials.

    Sample Deposition – Flat Plate (Bragg-Brentano)

  • plastic, aluminum or glass sample holder: dry sample in hollow space
  • avoid vertical loading (preferred orientation effects)


    Other Methods for Sample Deposition ((Bragg-Brentano)

  • Dry Dusting
  • Dusting in oil, grease, silicones, etc.
  • Back filling or Side Loading
  • Mixing with inert powder (wheat, cabosil®)
  • Volatile inert liquids (acetone, ethanol, etc.)
  • Non volatile suspending inert liquids (amyl acetate, + 5% collodion)
  • Non volatile suspending inert liquids (amyl acetate, + 5% collodion)
  • Spray drying (with “spherical” particles)
  • Thin film (for transparent materials and indexing procedures...)

    Note: often it is better to use a zero background plate as sample holder (Si or SiO2 monocrystal)


    Other Methods for Sample Deposition (Transmission)

  • Dusting on transparent films, with, or without, lacquers or inert liquids
  • Dusting on metal (C, Ni) grids

    Other Methods for Sample Deposition (Debye-Scherrer)

  • Capillary soaked into a liquid “ligand” (oils or paraffins) and then in dispersed powders. Mixing of liquid and powders can also precede the deposition.
  • Capillary loaded by gravity with dry powder and ultrasonic bath
  • Capillary externally covered by “sticking” powder
  • Sealed Capillary, with inert gases or mother liquors for unstable samples

    Preferential Orientation (or, is some cases, “Texture”)

    One of the basic assumptions of meaningful XRD is the homogeneous spatial and angular, distribution of the crystallite orientations in the different directions.

    Any deviation from homogeneity make sampling of intensities (the reproducibility of the measurement) rather difficult.

    Nevertheless, in a few cases, this effect is informative of the genesis and microstructure of the sample (deformed metal, geological sediments, rolling and cleavage, etc.).

    Elimination of preferred orientation effects (one of the most common experimental problems!) would not exist if the crystals were morphologically spherical.

    But the crystal world is intrinsically vectorial, not scalar, and anisotropy (structural and morphological) in the rule, not the exception!

    Preferred orientation, it not completely avoidable, must be reduced as much as possible, and later interpreted on the basis of cleavage properties or on the crystal structure (evidencing, whenever possible, sections with weak intermolecular contacts).

    Are accuracy values 2theta < 0.02° essential?

    Estimate of the significance of the results vs. the experimental accuracy, using numerical analysis of the diffraction peaks location.

    What is the best way to determine the TRUE (?) peak positions

    How strict is the requirement for high accuracy (not high precision!) ?

    Reference: Norberto Masciocchi, Data collection: Experimental set-ups and Sample Preparation, International Workshop on Structural Determination from Powder Diffraction Data, Villigen (CH), June 18-22 2008.

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