This helps to improve the counting statistics and minimizes the influence of preferred orientation of the powder which would otherwise result in deviations from the expected relative peak intensities. Moreover, due to the design of the instrument it is possible to spin the samples by using sample spinners. This ensures a very homogeneous temperature distribution around the sample. In contrast to direct heaters, environmental heaters are heating the sample from all sides. The second important type of heater is the so-called environmental heater (Figure 4, C). In contrast to that, very high temperatures (up to 2300☌) can be achieved with strip heaters. The advantage of the former is that a cryostat, that also allows cooling of the sample, can be introduced. Direct heaters are non-ambient XRD attachments that either have a sample holder that is placed on a resistance heater (Figure 4, A) or are so-called strip heaters, where the sample is directly placed on a resistively heated heating strip (Figure 4, B). In principal there are two types of heaters: direct heaters and environmental heaters. The investigation of these processes is not only interesting for the scientific community, but also for many technological processes used in industry.Īpplication examples will be given at the end of this article. Some of them are listed below:Īpplication fields: alloys, building materials, drug APIs, catalysts, minerals,…Īpplication fields: alloy, ceramics, polymers,…Īpplication fields: catalysts, zeolites,…Īpplication fields: building materials, pharmaceuticals, food industry,…Īpplication fields: catalysts, refractory materials, alloys,… These parameters result in a variety of material changes that can be investigated in-situ. The most important parameters are listed below: In non-ambient X-ray diffraction the sample is influenced by external parameters during the experiments. So far it has been explained what kind of information can be gained from X-ray diffraction experiments under ambient conditions. But these will not be further discussed here. More sophisticated methods of X-ray diffraction can be used to extract much more information from the samples. Also this effect can be quantified by XRD measurements. Microstrain in the sample also results in peak broadening. This can be used to extract information about the size of the crystallites. Crystallites that are smaller than ~120 nm give broader peaks. Crystallite Size and Strain: The crystallite size of the powder has an influence on the width of the obtained peaks.This can be especially interesting under non-ambient conditions. XRD allows characterizing the dimensions of this unit cell. The smallest building block of such a regular arrangement is the unit cell of the material. Unit Cell Lattice Parameters: As mentioned above crystalline materials are regularly arranged.Quantitative Analysis: If the sample is not a pure substance, but consists of several components, it is also possible to calculate the relative amounts of the individual phases.Comparison of the obtained data with databases results in the identification of the material. This can be seen as the fingerprint of the sample. Qualitative Analysis: Every crystalline material produces a specific diffractogramm.Obtainable information from a diffractogramm:
This is a plot of X-ray intensity on the y-axis versus the angle 2θ (2θ is defined as the angle between the incident and the diffracted beam) on the x-axis. The result of the measurement is a so called diffractogramm. As the wavelength in XRD experiments is known and the angles at which constructive interference occurs are measured, the use of the Bragg equation allows determining the distance between the lattice planes of the material. In words this equation can be described as follows: constructive interference occurs only if the path difference (given by 2d sinθ) is a multiple (n=1,2.) of the used wavelength of the X-ray beam. This is summarized in the famous Bragg – Equation: The magnitude of this path length only depends on the distance between the crystal planes and the incident angle of the X-ray beam. The resulting diffracted X-rays therefore have a different optical path length to travel. The incident X-ray beam is scattered at different planes of the material. Due to the crystalline nature, the atoms are arranged periodically. The dots in the graph correspond to the building blocks of a crystalline material. This is schematically shown in the next picture. This means that detectors can read-out a signal only at angles where constructive interference occurs. The scattered X-rays from the sample interfere with each other either constructively or destructively.
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