A brief introduction to XRD test analysis

Introduction to X-ray Diffraction (XRD) Testing

X-Ray Diffraction (XRD) is the main method to study the physical phase and crystal structure of a substance. When a substance (crystalline or amorphous) is analysed by diffraction, the substance is irradiated by X-rays to produce different degrees of diffraction phenomena, and the composition of the substance, crystalline type, intramolecular bonding, molecular configuration, conformation, and other characteristics of the substance determine that the substance produces a unique diffraction pattern.

XRD is the main method to study the physical phase and crystal structure of a substance, and it is one of the most commonly used material characterisation methods.XRD technology has the advantages of no damage to the sample, no pollution, fast, high measurement accuracy, and the ability to obtain a large amount of information about the integrity of the crystal, etc. Therefore, XRD as a modern scientific method of material structure and composition analysis, XRD has a wide range of applications in the fields of materials, biology, chemistry, medicine, machinery and other fields have a wide range of applications, XRD is widely used in the fields of materials, biology, chemistry, medicine, machinery and so on.

** X-ray Diffraction (XRD) Testing Applications **

In addition to general physical phase analysis, XRD can also be used for single crystal analysis, structural analysis, determination of microcrystalline dimensions, macro- and micro-stresses, and so on.

X-ray Diffraction (XRD) Fundamentals

When a beam of monochromatic X-rays is incident on a crystal, because the crystal is composed of regularly arranged atoms, the distance between these regularly arranged atoms is of the same order of magnitude as the wavelength of the incident X-rays, the X-rays scattered by different atoms interfere with each other, and strong X-ray diffraction occurs in some special directions, and the direction of the diffraction lines in the spatial distribution of the orientation and intensity are closely related to the crystal structure.

According to its principle, the diffraction pattern of a certain crystal has two main features: the distribution pattern of diffraction lines in space and the intensity of diffraction lines. The distribution pattern of the diffraction lines is determined by the size, shape and orientation of the crystal cell, while the intensity of the diffraction lines depends on the species of the atoms and their positions in the crystal cell.

Bragg's law: the difference between the wave ranges of two waves is 2dsinθ, when the difference is an integer multiple of the wavelength, i.e., 2dsinθ=nλ(n=0,1,2,3...), (θ is the angle of incidence, d is the spacing of crystalline surfaces, n is the number of diffraction levels, λ is the wavelength of the incident ray, and 2θ is the angle of diffraction), then the scattering waves will be in the same phase and will be mutually reinforced. All the scattered waves that satisfy Bragg's law are identical in phase, and their amplitudes reinforce each other, so that diffraction lines appear in the direction that makes an angle of 2θ with the incident ray. In the other directions, the amplitudes of the scattered rays cancel each other out, and the intensity of the X-rays is weakened or equal to zero.

Bragg's equation concisely gives the direction of diffraction of X-rays. That is, when the angle between the incident X-rays and one of the crystal planes (hkl) in the crystal satisfies Bragg's equation, diffraction lines are produced in the direction of their reflection lines, and vice versa.

Example of X-ray diffraction (XRD) analysis

(1) Spectral comparison method: Compare the spectra of the samples to be tested and the known phases, this method can be intuitive and simple to identify the phases, but the comparative spectra should be obtained under the same experimental conditions, this method is more suitable for the analysis of common phases and speculative phases.

(2) Data comparison method: the measured data (2θ, d, I/I1) can be compared with the standard diffraction data to identify the phases.

(3) automatic computer search identification method: the establishment of a database of standard phase diffraction data (PDF card), the measured data of the sample into the computer, the computer according to the appropriate procedures for retrieval, the main analytical software JADE, Search Match and so on.

Example of analysis: The figure below shows the XRD pattern of ZnO nanosheets loaded with different contents of gold nanoparticles. Compared with pure ZnO, the hybridised material showed obvious characteristic diffraction peaks of Au (JCPDS No. 04-0784) with the sequential increase of loading amount, so it was concluded that Au was successfully loaded on the surface of ZnO.