Recent content by M Quack

As you have probably found out by now, there are several notations for crystallographic point and space groups. The Hermann-Mauguin notation you are referring to is trying to be systematic, but somehow fails gloriously. The reason that there are up to 3 symbols is that there are up to 3...

In XRD, sharp peaks indicate long range order, and broad peaks short range order. Good crystals such as LaB6 or CeO2 calibration powders or Si single crystals have very sharp peaks. The peak width can be used to estimate the size of the ordered domains...

What you want to see in Raman scattering is inelastic scattering, where the frequency/wave length of the scattered light is different from the illuminating laser. On top of that signal you get a lot of elastic scattering "background" that you have to filter out. The usual way to do that is to...

Better late than never: The following may be of interest to you: Fourier Analysis in Polar and Spherical Coordinates https://lmb.informatik.uni-freiburg.de/Publications/2008/WRB08/wa_report01_08.pdf

For an ideal, infinite crystal, and using the kinematic theory of x-ray diffraction, there is intensity only at the Bragg positions, and nothing in between. Once you consider real (finite and imperfect) crystals and multiple scattering (dynamical theory of x-ray diffraction), things become a bit...

Measurements of the phonon dispersion curves (energy vs. momentum) are very standard in neutron inelastic scattering and to a lesser extent in inelastic x-ray scattering. In these experiments you detect single neutrons and x-ray photons. Each neutron/photon enters the sample will a well-defined...

The 4 Miller indices often used with hexagonal crystals are just a convenience. The 3rd index can be dropped. 4 indices are used to make planes with the same symmetry also "look alike" in the 4-notation. The physical reason is that the a- and b- axes form a 120 degree angle. There is a third...

In the real world there are no crystals in the strict sense: No crystal is perfectly periodic because they all have finite size. So a "periodic crystal" is always an approximation - in many many cases a very good approximation. In theory you can have a strained crystal with perfectly uniform...

Hi again, read and understand this here, then let me know if you still have questions. http://onlinelibrary.wiley.com/doi/10.1107/S0365110X67000970/abstract Angle calculations for 3- and 4-circle X-ray and neutron diffractometers W. R. Busing and H. A. Levy DOI: 10.1107/S0365110X67000970

There is an article by Batterman and Cole in Rev Mod Phys that has all the details of how to calculate dynamical diffraction curves. http://journals.aps.org/rmp/abstract/10.1103/RevModPhys.36.681

CDI is recording a diffraction pattern (reciprocal space) generated by a coherent beam. Using either several CDI images from overlapping positions of the sample or additional information (support), you can then reconstruct a real space model of the sample. It is not so different from normal...

Yes. you could see Si (X-type) as a special type of the GaAs (XY) type. There are even order-disorder phase transitions where at high temperature the X-position is filled with 50% atom A and 50% atom B, and at low temperature X=100% A and Y=100% B. Beta-brass is an example. More complicated...

The absorption of x-rays does increase a lot when you raise the photon energy above characteristic binding energies - so called absorption edges. This can be used for spectroscopy. You could say that for photon energies below the edge the material is more transparent than for photon energies...

In classical physics, kinetic energy is 1/2 mv^2 or p^2/2m. In QM the momentum p=hbar k...

Yes, pretty much, but only close to the minimum (electron) or maximum (hole) of the band. https://en.wikipedia.org/wiki/Effective_mass_(solid-state_physics)