FAQ
Frequently asked questions
-
X-ray diffraction is a non-destructive technique that probes the atomic arrangement of crystalline and partially crystalline materials. When a monochromatic X-ray beam hits a crystalline sample, the atoms act as a 3D diffraction grating and produce a pattern of peaks. From the positions and intensities of those peaks you can determine phase composition, lattice parameters, crystallite size and microstrain, preferred orientation (texture), residual stress, and more.
For deeper background, Rigaku’s X-ray diffraction technique page gives a concise overview of what XRD can and cannot do, with examples from many industries.
The “XRD Basics and Beyond” blog series expands that into more practical articles on powder, thin-film, high-resolution, texture and stress measurements.
-
For polycrystalline and thin-film samples, the most commonly used XRD modes are:
• Powder XRD in Bragg–Brentano geometry for routine phase identification and quantitative analysis of bulk polycrystalline materials (metals, ceramics, minerals, pharmaceuticals, cements, etc.).
• Thin-film and grazing-incidence XRD (GIXRD) for films, coatings and near-surface layers where the diffraction volume must be confined to the top few nanometers to micrometers.
• High-resolution XRD (HRXRD) for epitaxial layers, superlattices and semiconductor structures, where you care about strain, composition gradients and interface quality.
• Pole figure and texture measurements to map preferred orientation in rolled metals, drawn wires, additive-manufactured components and geological samples.
• Residual stress measurements based on the sin²ψ or related methods, used for welds, machined parts and formed components.
• Small-angle X-ray scattering (SAXS) and wide-angle scattering (WAXS) for nanostructure characterization (particle size, porosity, morphology) beyond the unit-cell scale. -
For powder diffraction, sample preparation is just as important as the instrument. You want a fine, homogeneous, randomly oriented powder in a flat sample holder. In practice that means grinding to a suitable particle size (often <10–20 µm for most materials), avoiding preferred orientation (for example, by using back-loading or side-drifted holders), and ensuring a smooth, level surface at the correct height in the diffractometer. Poor grinding, segregation or surface roughness will show up as peak broadening, spurious peaks or strongly distorted intensities.
-
The main factors you control are the X-ray source, optics, detector and scan conditions. Source power and wavelength determine intensity and penetration depth; optics (divergence slits, monochromators, Soller slits, parallel-beam versus focusing geometry) control resolution and background; detector type (scintillation counter, 1D/2D solid-state or hybrid pixel array detector) affects speed, dynamic range and ability to capture 2D information; and scan range, step size and counting time directly influence peak statistics and peak shape.
-
There is no one-size-fits-all recipe; it depends on phase complexity, required accuracy and available time. For simple phase ID in a well-known system, a moderate 2θ range and relatively coarse step size with shorter counting times may be acceptable. For quantitative phase analysis, structure refinement, crystallite size or strain analysis, you typically need a wider 2θ range, finer step size and longer counting times to get smooth peak profiles and good statistics in the background.
-
Phase identification matches your measured diffraction pattern against reference patterns for known materials, typically stored in large databases. Peak positions are used to determine lattice parameters and candidate phases; intensities and additional peaks or minor phases then confirm or reject candidates. The result is a list of phases present and often an estimate of their relative amounts.
Most modern XRD software can search against commercial databases (such as ICDD PDF-4) or user-defined libraries and report best matches with statistical figures of merit. -
Rietveld refinement is a whole-pattern fitting method where a structural model is refined until the calculated pattern matches the observed one as closely as possible. Instead of just using peak positions and peak heights, Rietveld analysis uses every data point in the pattern. This allows you to obtain accurate lattice parameters, atomic positions, site occupancies, microstrain, crystallite size, and robust quantitative phase analysis (including overlapping peaks and amorphous corrections when appropriate).r
You should consider Rietveld refinement when you need reliable quantitative phase analysis, are refining structures from powder data, or must separate heavily overlapping peaks. -
For thin films and surface layers, standard Bragg–Brentano powder geometry is often not ideal because most of the signal comes from the substrate. Grazing-incidence XRD (GIXRD) uses a very small fixed incidence angle so the X-ray beam only penetrates the top surface region, greatly enhancing film-to-substrate contrast. High-resolution XRD (rocking curves, reciprocal-space maps) probes epitaxial strain, layer thickness and interface quality, while X-ray reflectivity (XRR) gives film thickness, density and roughness even for amorphous layers.
-
Yes. Residual stress is determined by measuring how lattice spacings change as you tilt the sample relative to the beam. If the d-spacing varies systematically with tilt angle (ψ), that indicates elastic strain, which is converted into stress using appropriate elastic constants (sin²ψ method and its variants). This is widely used on welds, machined surfaces, shot-peened components and additive-manufactured parts.
Texture measurements collect intensities as a function of sample orientation to build pole figures, from which you reconstruct the orientation distribution function (ODF). This tells you how grains are aligned relative to sample axes, important in metals, polymers, geological samples and more.
Crystallite size and microstrain are estimated from peak broadening using line-profile methods such as Scherrer analysis or more advanced profile fitting within a Rietveld refinement.
-
XRD instruments use ionizing radiation, but modern diffractometers are engineered as fully enclosed systems with multiple interlocks, shutters and warning indicators. Under normal operation with all shields and interlocks intact, user exposure is negligible and well below regulatory limits. The real safety risks arise if shielding is bypassed, doors are defeated or users do not follow standard operating procedures.
Site-specific SOPs emphasize mandatory radiation safety training, correct startup and shutdown procedures, and clear rules against modifying optics or software settings beyond your training. -
You should start from your applications, not from the instrument catalog. Key questions are: what types of samples you will run (powders, bulk solids, thin films, small volumes), which measurements you actually need (phase ID, quant, Rietveld, stress, texture, SAXS, in-situ), how many users and samples per day you expect, and what level of automation and guidance your lab requires. Budget, footprint, service and upgrade path also matter.
Subscribe to the Bridge newsletter
Stay up to date with materials analysis news and upcoming conferences, webinars and podcasts, as well as learning new analytical techniques and applications.
Contact Us
Whether you're interested in getting a quote, want a demo, need technical support, or simply have a question, we're here to help.