XRD test is one of the commonly used tests, you may not know much about it, but this article will introduce you to the problems of the XRD test.

What is the use of XRD Test machine?

Can you see its purity? Or do you notice that it includes a particular functional group? When X-rays hit the material, scattering occurs. The coherent scattering of X-rays by crystalline substances is a diffraction phenomenon, that is, the incident beam does not diverge but its direction is changed and its wavelength remains unchanged when the incident beam exits. This is a characteristic of crystalline solids only.

The vast majority of solid-state substances are crystalline or microcrystalline or quasi-crystalline and can produce X-ray diffraction. A periodic long-range organized structure defines the crystal microstructure. The three-dimensional scene of the crystal microstructure, which contains all the details about the crystal structure, is physically transformed into the X-ray diffraction pattern of a crystal. Its X-ray diffraction pattern can be discovered using a small sample or quantity of solid powder.

Currently, the most powerful approach for studying crystal structure is XRD (X-ray diffraction) (such as the type and position distribution of atoms or ions and their groups, the shape, and size of unit cells, etc.).

XRD test machine

XRD is extremely useful for analyzing the phases of crystalline material. The number of diffraction peaks, angular positions, relative intensity order, and even the shape of diffraction peaks alters when the constituent elements or groups of crystalline substances are different or when the structures of those substances are different. As a result, the qualitative identification of the sample’s phase composition and structure can be completed by comparing the sample’s X-ray diffraction pattern to the X-ray diffraction pattern of known crystalline substances. The sample’s diffraction intensity data can be fully analyzed and calculated. XRD can do quantitative analysis of sample phase composition too.

XRD can also determine the size of the grains in the material or its orientation (texture of the material) and so on, the application is very common and extensive. At present, XRD is mainly applicable to inorganic substances and is less used for organic substances.

How to determine the quasi-crystalline structure of the sample from the XRD pattern?

How can you tell the difference between amorphous, quasi-crystalline, and crystalline structures in XRD patterns?

There isn’t a precise line that divides the three. If the sample is a more “crystalline” material, the resultant XRD XRD test pattern will have multiple or more generally independent narrow “spikes” (2 widths at half height in the 0.1°–0.2°; this width can be regarded as the “minimum width” of the crystal diffraction peak specified by the experimental conditions). If these “peaks” are greatly expanded, it may be established that the crystals in the sample have a particle size of less than 300 nm and can be referred to as “microcrystals.”

There is a Scherrer formula in the X-ray diffraction theory of crystals: the thickness of the crystal grains in the diffraction direction can be estimated from the amount of spectral line broadening.

The amorphous diffraction pattern is distinguished by a smooth shift in the intensity of scattered X-rays over the whole scanning angle range (from 2 12° to many tens of degrees), with one to multiple maxima values. Because the intensity of the direct beam is initially quite strong, it rapidly falls as the angle is increased and gradually trends to the instrument’s background value at a high angle.

From the point of view of the Scherrer formula, this phenomenon can be regarded as the result that the diffraction peaks of the crystal being greatly broadened, overlapped, and blurred due to the extremely fine grain size. The “short-range order” between particles like atoms or ions, which is the setting of the “amorphous” microstructure we imagine, is the limit of grain refinement. A maximum on an amorphous diffraction pattern relates to a frequently occurring interparticle distance in the amorphous. 

The “quasicrystalline” state is the transition between these two types and some “amorphous” materials.

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When doing X-ray diffraction, if a different target is used, will the spectrum be the same?

When doing X-ray diffraction, if a different target is used, such as a copper target or a Cr target, will the spectra of the two be the same? If different, do the position and intensity of the peaks change? Are there rules?

Different targets have different characteristic wavelengths. The diffraction angle (also often referred to as the Bragg angle or 2θ angle) is determined by the wavelength used in the experiment (Bragg equation). The use of different targets means that the wavelengths of X-rays used are different. According to the Bragg equation, the diffraction angle of a crystal face family with a certain spacing d will be different, and the diffraction angle of the crystal face family with each spacing value will show regular changes. . Therefore, the positions of the diffraction peaks on the diffractograms obtained by X-ray tubes using different targets are not the same, and the changes of the positions of the diffraction peaks are regular. 

A crystal’s own set of d-values is inherent in its structure and can be used as a marker parameter for the crystal substance. Therefore, regardless of the target X-ray tube used, a set of d values for a sample obtained from the obtained diffractogram is independent of the target material. The relative intensities between the diffraction peaks on the diffraction pattern are mainly determined by the crystal structure, but the absorption properties of the sample are also related to the wavelength of the incident rays. Therefore, the relative intensities of the diffraction peaks on the spectra obtained with different targets for the same sample will be slightly different, which is related to the target material. 

Revisit the Bragg formula and the intensity formula for diffraction, and you have all the answers to your questions.

The above is the arrangement of the three common problems of XRD. If you need an XRD test or the XRD instrument, you can contact Drawell XRD manufacturer.

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