# Tag Info

### Why does x ray diffraction take place in crystals as it seems to violate the law of conservation of energy?

For your concerns about energy conservation, the issue here is that you are considering the electron as essentially free, whilst in reality it is tightly bound to the crystal structure. The crystal ...
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### Medical X-Ray - why no diffraction?

Since the lattice spacing is about eight angstroms, the issue isn't any sort of unusual lattice spacing. Instead, the issue is that bones are thick. [Another answer points out that the crystals are ...
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### What did Feynman say about cesium chloride and body-centered cubic structure?

A Google search turned up the May 2016 IAS article Errors in The Feynman Lectures on Physics; Symmetry and Crystals by Rajesh Prasad, which I think explains the remark. In Vol. II, Section 30.4 of the ...
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### Interplanar distance in FCC and BCC

The formula $d_{hlk} = \frac{a}{\sqrt{h^2+k^2+l^2}}$ is a special case of the general formula: $$d_{hkl} = \frac{2\pi}{|\vec{G}|}$$ for a reciprocal lattice vector $\vec{G}$ to the case of a cubic ...
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### What is the unit and dimension of a matrix operator in quantum mechanics?

In scattering theory, $\hat V$ is a potential and has units of energy, while the Green's function is $$\hat G_0=(E-\hat H_0+i0^+)^{-1}$$ has units of the inverse of an energy. Therefore, there isn't ...
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### Determining Brillouin Zone for a crystal with multiple atoms

Lattice and crystal structure are two different things. A crystal structure is a convolution of a (Bravais) lattice with a basis (an atom or a group of atom). A lattice is a collection of geometrical ...
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### Distance between adjacent planes in a crystal

In answer to the question: adjacent planes are planes that are closest to one another when distance is measured along the normal to the plane. It is important to understand that every lattice point ...
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### Distance between adjacent planes in a crystal

I could only find this poor-quality picture. It should give you an idea, anyway. For example, consider the first picture in the first row: $(l,m,n)=(1,0,0)$ in that case, and it is easy to verify that ...
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### Determining Brillouin Zone for a crystal with multiple atoms

Option 2 is essentially the correct approach. Just as in the your Bravais lattice example, you begin by writing down the lattice vectors $\mathbf{a}_i$ of the real-space lattice. The lattice vectors ...
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### How can a monochromatic X-Ray tube produce a spectrum in XPS?

Because the X-rays, in the Photoelectron spectroscopy device, excite the electrons from the individual core levels out and as we know the electrons from the individual core levels reside in different ...
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### Is the Compton effect observed during regular x-ray diffraction?

Yes, in fact Compton scattering is often an annoyance in x-ray diffraction when you want to study the diffuse background from crystal defects and disorder. The amount of Compton scattering is highly ...
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### What is an example of an actual crystal with a primitive cell containing more than one atom?

Diamond and any diamond-like materials (silicon, GaAs, etc.). The most transparent example is probably graphene (since it is two-dimensional) - its primitive cell contains two atoms (referred to as A ...
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### How can a monochromatic X-Ray tube produce a spectrum in XPS?

Monochromatic X-rays produce electrons from a multiplicity of orbitals, producing a range of electron kinetic energies. One can analyze the outgoing electron energy to produce a spectrum. It's a ...
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### What exactly is the reciprocal lattice and how is it connected to the Ewald sphere?

Both descriptions are correct; some people prefer the geometric description: the lattice of atoms is replace by a collection of planes, with different orientations. This corresponds to the Bragg ...
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### Why are X rays in X ray crystallography diffracted by the electron clouds rather than nuclei?

Contemplate the difference in "size" of electron orbitals to the nucleus that is contained in the center: Atomic sizes are on the order of 0.1 nm = 1 Angstrom = 10^-10 m Nuclear sizes are on the ...
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### Structure factor calculation for non-cubic lattices

The common (at least in my field...) definition for the structure factor is $$S({\vec q}) = \frac{1}{\sum_{j}b_j^2} \sum_{j} \sum_{k} b_j b_k \mathrm{e}^{-i{\vec q}\cdot({\vec r}_j - {\vec r}_k)}$$ ...
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### Why the first peak in the X-ray diffraction of an amorphous solid has significantly high, in terms of intensity than the second peak?

In a perfectly crystalline solid the distances between the scattering planes are precisely defined so the scattering angles are precisely defined. In principle the XRD spectrum would show an ...
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### Can X-ray diffraction be applied to liquids, gasses or non-crystalline materials?

(I'm going to focus on protein crystallography here) Yes, in fact Small-angle X-ray Scattering, in which (usually) proteins are not in the crystalline state, is used extensively in biochemistry, ...
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### What kind of material could be used as a diffraction grating for Xrays?

You can use whatever single crystal you have. The cheapest high quality single crystals are Si wafers. Another more DIY-type option might be taking an old GPU or CPU die and grinding it off somewhat ...
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### Do neutrons change their wavelengths when diffracted?

X- rays can be treated with classical electromagnetic equations, and diffraction presupposes elastic scattering, so no (or very small) loss in energy. Neutrons are quantum mechanical entities and the ...
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### Number of Possible Primitive Vectors and Primitive cells in a Bravais Lattice

Consider any lattice with primitive vector triplet ($\vec{x},\vec{y}, \vec{z})$. Any lattice vector $\vec{v}$ can be written as $\vec{v} = v_x \vec{x} + v_y \vec{y} + v_z \vec{z}$ where $v_x, v_y, v_z$...
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### Physical meaning of Laue's condition for diffraction from crystals

But how can a 'particular vector' equal a set of vectors= Of course it is mathematical nonsense to say, a particular vector $\Delta\mathbf{k}$ is equal to a set of vectors. \Delta\mathbf{k} = \{ \...
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### How to convert intensity arbitray units to percentage in a XRD data?

If I have a raw xrd data then how should I convert my peaks arbitray unit intensity to percentage? In olden days visual intensity scale was used by us in the interpretation of single crystal ...
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### Spot intensity in x-ray-crystallography

An interesting question. The reason is due to the mosacity in the crystals, the Bragg peaks spread and so their intensity is not measured properly, usually 0.1 degree rotation is needed to get 'full' ...
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### How do visualization programs generate electron density meshes?

Starting from the end: map → isosurface If you have electron density values in the form of 3D discrete scalar field (i.e. values on a 3D grid) you can use a computer graphics algorithm, such as ...
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The Wigner-Seitz cell of a bcc lattice is not cubic, i.e. the angles $\alpha$, $\beta$, $\gamma$ are not 90°. They are actually around 109.3°. Therefore you have to build your reciprocal lattice with ...