Questions tagged [crystallography]

For questions concerning crystalline structures and their properties.

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2answers
284 views

Why is the base-centered orthorhombic crystal lattice a unique crystal system?

I'm having difficulty understanding why the base-centered orthorhombic crystal system is a unique crystal system. When I draw two base-centered orthorhombic unit cells next to each other there appears ...
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35 views

Interatomic distance of alloys [closed]

In pure crystals the interatomic distance is well defined. For example: In a carbon crystal lattice, it is the distance between 2 carbons. However if we have an alloy (e.g., Silicon-Germanium), how ...
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67 views

Why is U the symbol for lattice energy?

I often see $U$ or even $\Delta U$ being the symbol for lattice energy. Why is that? Does it refer to internal energy?
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1answer
22 views

Miller Indices of Goldnanoparticles from Turkevich and Frens method

I need the miller indices of gold nanoparticles that were synthesized after the route of Turkevich and Frens. I during my research I found a lot of publications, but it looks like no one measured it ...
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0answers
84 views

How to find the atomic packing factor of Sodium Chloride (and other FCC ionic compounds in general)?

For a piece of coursework I am doing, I need to calculate the atomic packing factor of some ionic compounds. I have had no formal teaching in this area, so what I know comes from information I have ...
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1answer
34 views

What is meant by “basis” in “… its basis in particles leads to a material comprising crystallites or grains tightly bound together, …”?

I am currently studying Ultrasonic transducers – Materials and design for sensors, actuators and medical applications by Kentaro Nakamura. In chapter 1.2.1 Ferroelectricity, the author says the ...
4
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1answer
81 views

What is the precision of intensity data in XRD measurement?

I made some relative crystallinity measurements on a zeolite (crystalline aluminosilicate). Which is measured for a specific peak area and compared with a reference sample. The XRD of powder patterns ...
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1answer
73 views

Can a crystal structure of a substance appear or disappear?

I read somewhere before that some substances no longer crystallize naturally in some specific structures, although it do that readily before. Instead, new structures that never happen before become ...
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0answers
32 views

Could someone advise me on sources for crystallography and surface sciences?

I'm a physicist learning crystallography and surface science on the side of my research and I came across the concepts: surface reconstruction in hexagonal materials, unit mesh of surfaces, etc. I was ...
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25 views

Conventional unit cell for a hexagonal crystal system

The figure shows a unit cell of a hexagonal crystal system. Drawn in bold, is the unit cell. The lightly shaded one is a unit cell as well and has a six fold symmetry along an axis, hence is more ...
3
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2answers
98 views

Trouble understanding interplanar spacing using miller indices

We know that two parallel planes have the same Miller indices, this implies that we can have an infinite number of parallel planes close to one another all of which have the same Miller indices. But ...
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1answer
71 views

How to differentiate hydrous and anhydrous compound? [closed]

For an experiment, my teacher gave me containers of hydrates and their corresponding anhydrous compounds, but I have a feeling that for one of the compounds she switched the hydrate and anhydrous ...
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2answers
79 views

If stirring negatively affects crystal purity, why is it so?

My Intellectual Expectations Intuitively, I would expect strong stirring to improve crystal purity during the process of crystalization. My rationale is that strong stirring would increase contact ...
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1answer
28 views

The formation of ice crystals on/in frozen food that has been defrosted and then frozen again

I made a mistake. I put my ice cream in the refrigerator instead of the freezer and left it there for a night. I realized my folly the next day. I put it in the freezer. When I took it out, I noticed ...
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42 views

What does the order of a class mean in a character table?

I am not from a chemistry background. I am trying to see how the symmetry operations affect the stiffness tensor which led me in the path of understanding character tables. I am looking at the ...
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0answers
12 views

Examples of application of surface area maximization to crystallography or molecular geometry

Suppose that N points are chosen from the unit ball (or its boundary, the sphere) in three-dimensional space R^3. Consider the convex hull of these N points (assume N is at least 4). The resulting ...
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3answers
429 views

Are crystallographic omit maps only used with molecular replacement?

(This is in the context of macromolecular X-ray crystallography.) From Lamb et al. 2015: Model bias is the result of how maps are calculated: because the phase estimates [of the structure factor] for ...
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3answers
376 views

If you accumulate 100 identical spheres how many will end up on the surface?

So far I have asked this question in physics, engineering and math sections but have not gotten an answer in three years. If you have 100 identical spheres and group them into A sphere shape, how many ...
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1answer
46 views

Change of ionic packing upon crystals are pressurized

When rock salt crystal is pressurized, its FCC structure changes to BCC structure whereby coordination ratio changes from 6:6 to 8:8. At the same time packing efficiency of the crystal decreases from ...
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1answer
63 views

Will these K-alum crystals combine into a “cohesive/well-glued” mass?

The attempt to make a single solid mass of K-alum, using over 125 grams of McCormick K-alum powder, has resulted, in less than 2 hours, in: So besides the growth around the loop of the seed "...
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1answer
207 views

How do I find miller indices for a plane whose intercepts are fractions of the lattice constant?

[I'm talking with respect to cubic lattices alone.] For instance, if a plane has $x,y,z$ intercepts $a/2,a/2,a/2$ (where $a$ is the lattice constant) the miller index would be $[2\space2\space2]$. The ...
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2answers
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Is there a standard scholarly reference for lattice constants of crystals of the elements?

I need to discuss the lattice constants of bulk crystals of several metal and semiconductor elements. I can find plenty of tables and numbers that are probably "close enough" but for a paper ...
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25 views

Any open-source to animate 2D materials in 3D. (e.g. van der Waals heterostructures, 2D crystal layers etc.)

I want to model different 2D nano-structures, layered materials in 3D (animated version). Is there any open source where I can build these structures. Like this:
3
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1answer
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Why should the scalar product of the components along two axes remain unchanged after transformation?

A couple of proofs from Chapter 2 of "Space Groups for Solid State Scientists" are giving me a hard time (see attached image). So what I understand is: "r" was the original ...
2
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1answer
853 views

Converting fractional coordinates into cartesian coordinates for crystallography

So let's say for a given molecule I have the volume of a unit cell, the shape of the unit cell (monoclinic, cubic, etc), the cell angles alpha, beta, and gamma, the cell lengths a,b, and c, and a list ...
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345 views

How to find bond lengths from .cif files of crystal structure

I am confused about how to calculate the bond lengths within a given structure given its .cif file. I have highlighted the bond of interest in the image below. The atom coordinates are shown in the ...
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25 views

What is meant by “rotation about an axis that passes through a lattice point”?

I am currently studying Introduction to Solid State Physics, 8th edition, by Charles Kittel. In the section Fundamental Types of Lattices of chapter 1, the author says the following: Crystal lattices ...
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0answers
19 views

Crystmet or alternative metals/alloys/intermetallics powder diffraction database

Does anyone know what happened to Crystmet, the metals structure database? The website seems to have disappeared. Is there any way to access the database or is there a recommended powder diffraction ...
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2answers
99 views

Sketching lattice points, primitive axes, primitive cell, and basis of atoms

I am currently studying Introduction to Solid State Physics, 8th edition, by Kittel. Chapter 1 provides the following figure and accompanying explanations: It also says the following: An ideal ...
3
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1answer
46 views

Free refined value in Rietveld

I have a question about Rietveld refinement The author of this paper claimed that the free refined CN ligand is 1.081. However, they does not show how they got that number. They stated it was based ...
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2answers
195 views

Why rutile structure have primitive unit cell instead of body centered?

In the literature (Wikipedia), I read that $\ce{MgH2}$ have a structure of rutile. Then, I looked at its space group which is $P4_2/mnm$. From this notation, I understood that it possesses a (...
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419 views

What are the limitations of the Born-Lande' equation?

The Born-Lande' equation is used to theoretically calculate the lattice energy, $\Delta U$, of ionic compounds. It is often cited as such in literature, $$\Delta U = -\frac{k_Az_1z_2Me^2}{4 \pi \...
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1answer
510 views

Bonding and coordination of oxygen in a Ga2O3 crystal structure [duplicate]

I'm trying to find the crystal structure of gallium oxide ($\ce{Ga2O3}$). However, I find the images of the crystal structure in the peer-reviewed journals problematic. First, I hop to the wikipedia ...
3
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1answer
98 views

Origin in a crystal

I am trying to understand the International Tables for Crystallography. How can I identify the origin in the image on the left? Without knowing the origin, I cannot identify the position of the ...
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0answers
20 views

How to Visualize the crystal planes of calcite?

I've been struggling to visualize the structure of calcite. Most papers say it grows in a rhombohedron capped by (104) faces. However, I don't see why it would do this when looking at it using ...
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49 views

Reason behind more prioritising of normal spinels

According to my textbook: In normal spinels $\ce{A^{II}}$ should have occupied octahedral voids, but this factor is outweighed by greater lattice energy or smaller cation $\ce{B^{III}}$. Later, ...
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1answer
2k views

Calculate third and fourth nearest neighbours in fcc packing [closed]

My textbook has given data for third and fourth nearest neighbours to be 6 and 8 with distances  a and √(3/2)a. I have been able to calculate for the first and second nearest neighbour but it has ...
0
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1answer
81 views

Cation-anion radius ratio of manganese difluoride

How to determine the cation-anion radius ratio for $\ce{MnF2}?$ I tried to calculate the $r_\mathrm{c}/r_\mathrm{a}$ ratio using the relationships: $$2r_\mathrm{c} = c$$ and $$(2r_\mathrm{c} + 4r_\...
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1answer
157 views

Does a unit cell have to contain a whole number of atoms?

I was given this problem recently to compute the number of ions in a unit cell of ferrous oxide $\ce{FeO}$. The data given was: Side length $a = \pu{5 Å}$ Density $d = \pu{4 g/cc}$ Using the formula ...
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1answer
32 views

PdPS interlayer distance [closed]

PdPS is being considered as a layered material but when I look at its crystal structure it does not look like that. Fo example I could not figure out its interlayer distance. Does anyone familiar with ...
0
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1answer
174 views

HCP unit cell c-axis

Today I was asked to show that the perpendicular height, $H,$ of a regular tetrahedron is related to the length of a side, $L,$ of the tetrahedron, by $H = \sqrt{(2/3)} \cdot L$. I did this no problem....
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31 views

Why are colloidal dispersions stable? [closed]

Smaller particles in a colloidal dispersion are less stable than larger ones due to their higher surface to volume ratio. Therefore Ostwald ripening occurs, a process which promotes growth of larger ...
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2answers
134 views

What happens to the crystal structure of ice as it gets colder and colder [duplicate]

Not sure if this belongs on Chemistry or Physics stackexcahnge. As water freezes into ice, it turns into a solid, and expands as it forms a crystal structure. But what happens to this crystal ...
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0answers
84 views

Data-processing pipeline for protein x-ray crystallography: uncertain of terminology and order of procedures [closed]

Background: I am trying to get an overview of the data-processing pipeline for solving protein structures by x-ray crystallography, and in a very simple way understand what mathematical procedures are ...
3
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2answers
356 views

Importance of zinc blende and wurzite crystal structures for semiconductors?

I am currently studying the textbook Physics of Photonics Devices, Second Edition, by Shun Lien Chuang. In a section discussing the basic concepts of semiconductor band and bonding diagrams, the ...
5
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1answer
473 views

How do the three Miller indices (hkl) denote planes orthogonal to the reciprocal lattice vector?

The Wikipedia page for Miller indices defines Miller indices as follows: There are two equivalent ways to define the meaning of the Miller indices: via a point in the reciprocal lattice, or as the ...
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1answer
131 views

Miller Indices and the case of a cubic crystal

My textbook, Solid-State Physics, Fluidics, and Analytical Techniques in Micro- and Nanotechnology, by Madou, presents the following image and explanation in a section on x-ray diffraction and Laue ...
2
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1answer
421 views

Do we really have technology with the resolution to distinguish between layers of single atoms of materials?

My textbook, Solid-State Physics, Fluidics, and Analytical Techniques in Micro- and Nanotechnology, by Madou, says the following: X-ray analysis reveals the symmetries of crystals (lattice type), ...
3
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1answer
91 views

Interstitial defects in crystals: “high energy configurations”?

In the Wikipedia article on crystallographic defects, a type of point defect known as an interstitial defect is described as follows: Interstitial defects are atoms that occupy a site in the ...
3
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1answer
264 views

Structure of crystalline boron trioxide

I recently came across the statement The structure of crystalline $\ce{B2O3}$ consists of $\ce{BO4}$ tetrahedra, two sets of which form two types of interconnected spiral chains, three $\ce{B-O}$ ...