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Glossary

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Amorphous
Adjective describing the lack of translational symmetry in a substance. Amorphous substances do not show any diffraction peaks. Sometimes such materials are termed aperiodic.
Antiscatter Slit
First part of the secondary optics, reduces diffuse scattering and limits height divergence of X-Ray beam.
Characteristic Radiation
Radiation caused by electronic transitions inside the electron shell when an atom achieves a lower state of energy.
Copper Tube
X-Ray tube with copper as anode material – the most frequently used X-Ray tube in Powder diffraction.
Crystalline
Adjective describing the presence of translation symmetry in a substance. Crystalline substances show discrete characteristic peaks in their diffraction patterns.
Crystallite
Term for tiny crystals, too small for the unaided eye to detect.
d-spacing
The distance between the planes of a crystalline solid. The intensity of the d-space pattern is directly proportional to the number of electrons (atoms) that are found in the imaginary planes. Every crystalline solid will have a unique pattern of d-spacings (known as the powder pattern), which is a “finger print? for that solid.
Diffraction
The scattering of waves by objects they interact with. Diffraction effects are most powerful when the diffraction objects are regularly spaced, and the spacing is similar in size to the incident wavelenght.
Diffraction Pattern
Diffractogram of a substance – can be used as a fingerprint to identify it. (Never call a diffraction pattern a spectrum)
Diffractogram
A plot of diffracted X-Ray intensities versus the scanning angle 2θ as abscissa.
Diffractometer
Instrument to analyze the crystal structure of materials by investigating their diffraction patterns. A powder X-Ray diffractometer consists in a radiation source, primary optics, a sample holder, and a detector which scans the sample along the 2θ cycle.
Divergence Slit
A simple slit that limits the height divergence of the X-Ray beam. The divergence slit is part of the primary optics and located after the primary soller slits.
Grazing Incident
The incident beam angle is kept constant and below 5° – method to investigate thin films.
Kα-radiation
Most intense characteristic radiation – actually consists in two lines α1 and α2 with a ratio of 2 to 1.
Monochromator
A device that selects certain lies of the characteristic radiation and suppresses all other lines and white radiation.
Phase
Frequently used term for a sample component. Phases can be crystalline or amorphous compounds.
Primary Optics
X-Ray optics between X-Ray source and sample.
Receiving Slit
Last part of secondary optics – limits height divergence of X-Ray beam.
Reflection Geometry
X-Ray source and detector are on the same side of the sample – most frequent geometry.
Sample Displacement
A slight misplacement of the sample from ideal position – leads to a shift of the observed signal position from the actual one.
Scintillation Counter
Most common type of X-Ray point detector. The scintillation counter first converts X-Rays into visible light, then in photoelectrons and amplifies it with a photo electron multiplier.
Secondary optics
X-Ray optics between sample and detector.
Size Broadening
Broadening of diffraction peaks due to small crystallite sizes well below 200 nm.
Soller Slit
An array of parallel slits that reduces the axial divergence of an X-Ray beam. Soller slits constitute an integral part of both primary and secondary optics.
White Radiation
Radiation which is caused by the continuous deceleration of electrons as they pass the nuclear cores of the anode material.
X-Ray
Electromagnetic waves with a wave length smaller than 10 but larger than 0.01 nanometers. This range coincides with the range of interatomic distances in materials. Therefore X-Rays are scattered by crystalline materials and give a three dimensional diffraction pattern, a subset of which is captured by the detector and presented as a two dimensional plot.
X-Ray Tube
Most common type of X-Ray source – consists in an evacuated tube, a cathode, an anode and beryllium windows. Electrons are accelerated onto the anode material with voltages up to 50 kilovolts. Through interaction with the anode material they lose their kinetic energy, some of which is emitted as X-Rays. The X-Rays are let out via the beryllium windows.