X-ray crystallography (X-Ray Diffraction or commonly referred to as XRD) is a tool used for identifying the atomic and molecular structure of a crystal, in which the crystalline atoms cause a beam of incident X-rays to diffract into many specific directions because X-ray wavelengths are of roughly the same size as the interatomic spacing of a crystal, significant diffraction of the waves occurs. Due to the regularities inherent in a crystal structure, monochromatic X-rays are diffracted at various angles with different intensities. By measuring the angles and intensities of these diffracted beams, a crystallographer can produce a three-dimensional picture of the density of electrons within the crystal. From this electron density, the mean positions of the atoms in the crystal can be determined, as well as their chemical bonds, their disorder, and various other information. Since many materials can form crystals-such as salts, metals, minerals, semiconductors, as well as various inorganic, organic, and biological molecules—X-ray crystallography has been fundamental in the development of many scientific fields.
In its first decades of use, this method determined the size of atoms, the lengths and types of chemical bonds, and the atomic-scale differences among various materials, especially minerals and alloys. The method also revealed the structure and function of many biological molecules, including vitamins, drugs, proteins, and nucleic acids such as DNA. X-ray crystallography is still the chief method for characterizing the atomic structure of new materials and in discerning materials that appear similar by other experiments. X-ray crystal structures can also account for unusual electronic or elastic properties of a material, shed light on chemical interactions and processes, or serve as the basis for designing pharmaceuticals against diseases.
In a single-crystal X-ray diffraction measurement, a crystal is mounted on a goniometer. The goniometer is used to position the crystal at selected orientations. The crystal is illuminated with a finely focused monochromatic beam of X-rays, producing a diffraction pattern of regularly spaced spots known as reflections. The two-dimensional images taken at different orientations are converted into a three-dimensional model of the density of electrons within the crystal using the mathematical method of Fourier transforms, combined with chemical data known for the sample. Poor resolution (fuzziness) or even errors may result if the crystals are too small, or not uniform enough in their internal makeup.
X-ray crystallography is related to several other methods for determining atomic structures. Similar diffraction patterns can be produced by scattering electrons or neutrons, which are likewise interpreted by Fourier transformation. When growing single crystals is not possible, which is mostly the case, Crystalline powders Which mainly consist of millions of small crystals with random orientations can be analyzed in a Powder XRD. X-ray methods can be applied to obtain other detailed information; such methods include fiber diffraction, powder diffraction, and (if the sample is not crystallized) small-angle X-ray scattering (SAXS).
In the last century, 27 Nobel prizes have been awarded for discoveries directly resulting from the use of X-ray crystallography. The impact of the Yorkshire-born family’s work can be put no better than by Max Perutz, a recipient of one of those 27 Nobels.
Why water boils at 100ºC and methane at -161ºC, why blood is red and the grass is green, why diamond is hard and wax is soft, why glaciers flow and iron gets hard when you hammer it, how muscles contract, how the sunlight makes plants grow and how living organisms have been able to evolve into ever more complex forms, the answers to all these problems have come from structural analysis.
- Powder XRD – this can be configured for normal Powder XRD, Thin Film XRD, Variable temperature or variable pressure, Electrochemical XRD, XRD combined with DSC, Piezo, etc.
- Single Crystal XRD– this can be configured for small molecule or macromolecule XRD.
- SAXS– this can be configured as SAXS with Powder XRD or dedicates SAXS system either for material science or biosciences
- Online XRD- for Semiconductor, Galvanizing line or other coatings, Clinker line, etc.
The market for XRD is expanding internationally and in India rapidly. Earlier it used to be very much Academic but today most of the users are using this technique as a daily tool and more so in Industry. Some of the Industry which are using this technique extensively are listed in the table below:
|1||Pharmaceutical||Crystal Structure, Phase, Crystallinity, Particle Size and shape in nm range.|
|2||Automobile & Aerospace||Phase, Residual Stress, Orientation and Retained Austenite|
|3||Polymer & Plastics||Phase, Crystallinity, Crystal Structure, Phase, Crystallinity, Particle and Pore Size/Shape in nm range and Orientation|
|4||Petrochemical||Phases in various Catalysts and also particle size and shape analysis.|
|5||Renewable Energy including Battery||Crystal Structure and Phase|
|6||Paint & Dyes||Phase, Crystallinity and particle size|
|7||Mining & Minerals||Phase, Crystallinity, particle size and sometime Structure|
|8||Metals (Ferrous & Non-Ferrous)||Phase, Orientation, Residual Stress, Crystallite Size.|
|9||Catalysts & Chemicals||Crystal Structure, Phase, Crystallinity, Particle Size and shape in nm range.|
|10||Cements & Food||Phase and Crystallinity|
|11||Food||Phase, Crystallinity, Orientation, Particle Shape and size and EXAFS.|
Keeping the needs of the Industry in mind many dedicated XRD systems are being manufactured (Dedicated SAXS, Residual Stress Analysers, etc). Many attachments to these techniques are also getting introduced regularly for better study of materials like Variable Temperature, Variable Pressure, DSC, Electrochemical Cells, Variable Magnetic, and Electric Field environments.
Presently new types of 1D and 2D detectors and special advanced software are making XRD more accessible, easy to use, and fast.
The market share of each type of XRD Internationally and evolved similarly to the Indian market, depicted in the following pie chart.
The main driving Industries for XRD in the next few years in India Will be Pharmaceutical, Biotechnology, Nanomaterial research, Steel, Cement, Automobile, Heavy Industries, Renewable Energy, Government R&D projects, and Universities.
India is slowly emerging as a pivotal country for X Ray Crystallography with ASCA which was held in Kolkata and the biggest event in X Ray Crystallography, IUCr 2017 was held in Hyderabad India.