Questions tagged [crystal-structure]

In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid.

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6
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1answer
270 views

Determining structure factors for crystals from lattice and motif

I understand that the structure factor for a crystal is given by: $$F_{hkl} = \sum_r f_{r} e^{2{\pi}i(hx_{r}+ky_{r}+lz_{r})} $$ My textbook (''Structures of crystals'', Glazier) suggests that you ...
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How is the height between two non consecutive layers of Face Centred Cubic not equal to two times the side length?

In my textbook it says that the height between two consecutive layers of face centred cubic is 2*side length * root 0.6666 which also happens to be the height between two non consecutive layers of a ...
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How is this crystal structure of SnCl2 correct?

Tin has 4 valence electrons. In the picture it has made 3 covalent bond with Chlorine atoms. So, there should be one odd electron remaining. But the picture shows a lone pair( 2 free electrons ...
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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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2answers
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Stoichiometric defects in silver bromide

Stoichiometric defects (Schottky and Frenkel defects) in ionic crystals are formed due to irregularities in the ionic arrangement which maintain the stoichiometry and electroneutrality of the solid. ...
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1answer
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If I break a crystal, would the “broken” pieces also have the same crystal shape? [closed]

If I've a crystal of some particular geometrical shape and i hammer it and it breaks into small pieces. Will the small pieces have the same shape as of the parent crystal?
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Primitive cell of the bcc (body-centred cubic) lattice

I am currently studying Introduction to Solid State Physics, 8th edition, by Charles Kittel. In the section Three-Dimensional Lattice Types of chapter 1, the author presents the following figures: I ...
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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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1answer
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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 ...
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1answer
33 views

Microscopic image [closed]

When I was reading a chapter on solids structure then i thought of how the real structure would be like if seen from microscope. Hence I want the real microscopic molecular image of NaCl(common salt) ...
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How is the Born-Lande equation modified when the structure is not NaCl?

Often the Born-Lande equation is quoted (alongwith the calculation of the Madelung constant and Born exponent) with reference to rock-salt structure. But what if we take some other crystal, like ...
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Is LiNbO3 a perovskite or not?

I am collecting a database of perovskite materials and could not decide if $\ce{LiNbO3}$ is categorized as perovskite or not. $\ce{LiNbO3}$ has been identified as a perovskite [1] as well as non-...
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What are the signs in `_atom_site_label` in a CIF file mean?

I am trying to write a program that will be able to read CIF files. I am testing on a CIF file like this: ...
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2answers
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Dihedral angle of gaseous and crystalline HOOH

Why does hydrogen peroxide exhibit a dihedral angle of $111.5^\circ$ in the gaseous state? And a dihedral angle of $90.2^\circ$ in the crystalline phase? I know that in general, there is likely to be ...
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2answers
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How many nearest neighbours does a corner atom have? [closed]

Figure shows a unit cell of a cubic lattice. The atom in the middle has 8 nearest neighbours (the atoms in the corner). How many nearest neighbours does a corner atom has ? I identified the given ...
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Determining cation-to-anion radius ratio for “ideal” Anti-fluorite structure

My book under the heading of Anti-fluorite structure makes the following remark, about the radius ratio of an ideal Anti-fluorite: The ideal antifluorite would have a cation-to-anion radius ratio ...
2
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1answer
54 views

Is an amorphous solid a single phase? [closed]

Amorphous solid possess short-range order but no long-range order (e.g. amorphous silica, the short-range order is originated from the tetrahedral bonding between Si and O). Is it possible to have ...
3
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1answer
208 views

Rietveld (FullProf) general background function

I was reading through Eric Mittemeijer's book 'Modern Diffraction Methods' when I found the following statement in the Rietveld chapter by Robert Dinnebier. It is common practice to use orthogonal ...
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Get fractional coordinates from special Wyckoff positions (IUCr)

I'm trying to get the fractional coordinates for Mo and S, for MoS$_2$-2H, where 2H means the phase. MoS$_2$-2H is a bilayer, in which each layer is separated from each other by Van der Waals forces. ...
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Conception and manufacture of the Avogadro Project's (nearly) perfect silicon sphere (and, what is “atomic feeling”?)

The Avogadro Project, an effort prior to the recent redefinition of Avogadro's constant to design a nearly perfect sphere of silicon-28, apparently relied on the fine fingers of optician Achim ...
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2answers
80 views

How to identify if a material is perovskite or not?

This is more of a materials science question, but I believe many of you have referred NIST Inorganic Crystal Structure Database (ICSD) database. I am collecting a database of perovskite materials and ...
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1answer
49 views

Are HCP and Primitive Hexagonal Unit Cell the same thing? [closed]

In HCP, the [2D] Hexagonal packed layers are arranged in ABAB form. The same happens in Primitive Hexagonal Unit Cell. So does that mean they are the same? If not what differentiates one from the ...
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2answers
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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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1answer
48 views

An automated approach to visualize several xyz structures

I have several .xyz files (each composed of several molecules) and I'd like to find an automated way to visualize and save them. I'd appreciate any guidance.
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1answer
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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 ...
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1answer
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How to formally calculate the surface density of layered materials such as graphene?

Typically density is defined in units of mass per volume. In the case of graphene it is mass per area, i.e. surface density. What would be the correct way to calculate the surface density (mass per ...
3
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1answer
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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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36 views

Does a [B4O8]4- anion really exist?

I am currently collecting information for an abstract and therefore I wanted to discuss different $\ce{[BO3]^3-}$ and $\ce{[BO4]^5-}$ connectivities. I also found a book on crystallography and the ...
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1answer
30 views

Chemical bonding and crystal structure of silicon [duplicate]

I can understand that in Silicon Crystal a central Silicon atom shares its 4 valance electrons with 4 surrounding silicon atoms. And the chain continues. But then What happens to the outermost such ...
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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 ...
4
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1answer
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Understanding lattice matching of graphene on silver (111) crystal surface and meaning of the √3 x √3 lattice?

Figure 1 in Ivor Lončarić and Vito Despoja, Phys. Rev. B 90, 075414 Benchmarking van der Waals functionals with noncontact RPA calculations on graphene-Ag(111) (available in Researchgate) shows a ...
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3answers
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Choice of doping elements in semiconductors

In a typical semiconducting material, we start with silicon (group IV) and introduce atoms of group V or group III depending on whether we are constructing an n- or p-type semiconductor respectively. ...
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How to construct this spinel crystal structure?

I'm attempting to rebuild the crystal structure of γ-Al2O3 from calculated crystallographic data and am having some trouble. The primitive cell is repeated three times along the c-axis, leading to ...
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How to create .CIF file from DRX data in a paper, for compound not found in crystallographic database

I tried to recover a .CIF file with the crystal structure for the compound discussed in this 2006 paper, strontium hydroxide octahydrate - $\ce{Sr(OH)2·8H2O}$ - from Cambridge Crystallographic Data ...
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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
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Replacement for optical calcite (Glan Thompson prism)?

I notice that Glan Thompson prisms seem to be the preferred optics for doing polarimetry and have been for at least 75 years. One instrument maker says that polaroid films can be used but they tend to ...
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0answers
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Why upon melting of PEO between crossed polars colours appear?

Crystalline PEO when under crossed polars shows distinct Maltese cross pattern. Being birefringent, when polymer crystal align with the polarizer or analyser it shows extinction regions (effect known ...
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2answers
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Why are so many ionic compounds brittle?

Even when ionic compounds are strong (e.g. rubies and sapphires), they are neither malleable nor ductile in the slightest, and if sufficient stress is put on them, they will shatter, not bend. Why is ...
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1answer
238 views

Is the number of tetrahedral voids always equal to double the number of octahedral voids in any crystal?

I came accross the question whether the number of tetrahedal voids is always equal to twice the number of octahedral voids (in the case where both the voids are present). The key was given as the ...
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1answer
34 views

Unit cell structure of ionic crystal

I have a question about the structure of an LiH unit cell, and while this is related to a homework problem, it isn't the problem itself, I'm just looking for conceptual understanding. I've already ...
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2answers
385 views

Stacking two square (2D) layers to make a 3D close packed structure

My textbook states these ways of stacking 2D layers to make 3D close packed structures: Square close packing layer over Square close packing layer (though not written explicitly, the illustration ...
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1answer
28 views

XRD: Can stacking faults cause pseudo-centring?

Consider a cP lattice with a = 10 Å and an octahedron residing on each of the unit cell's vertices as shown below: The maximum symmetry will be Pm-3 m. Now, let's consider there are stacking defects ...
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1answer
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Melting point of crystalline solids

Why crystalline solids have sharp melting points but melting point of amorphous solids vary within a range? Is it because the interaction energy is equal between atoms of crystalline solids so they ...
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1answer
47 views

Why are crystalline solids anisotropic? [closed]

Why crystalline solids are anisotropic whereas amorphous solids are isotropic? Is it because in crystalline solids, X, Y and Z dimensions vary, but so does in amorphous. Please write as simple as ...
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1answer
71 views

Are clathrates and interstitial compounds the same thing?

In the book$\ce{^{[1]}}$, it's given that clathrates are compounds in which gases are entrapped within cavities of crystal lattices of certain organic or inorganic compounds. Interstitial compounds ...
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Trying to synthesize and crystallize iron (iii) ammonium sulfate

I've been following instructions (from here, the first method) to synthesize iron (iii) ammonium sulfate and crystallize it. The first attempt was a fail, I spilled most of my solution and what I ...
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1answer
52 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
716 views

Distinguishing between octahedral and tetrahedral holes

I know the question sounds a bit silly and there are many similar answered questions but my 3D visualization (imagination) is very bad. There are some images of octahedral and tetrahedral holes but ...
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1answer
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Copper (II) Acetate from 5% vinegar + salt, electrochemically

I'm trying to create Copper (II) Acetate crystals, but in these times of Coronavirus it's difficult to come by hydrogen peroxide. I could be patient, but I'm not, so I'm trying to make it ...
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1answer
60 views

Is there a crystal structure of ammonia in ionic form?

Like solid $\ce{PCl5}$, does solid $\ce{NH3}$ exist as $\ce{[NH4+][NH2-]}$ (i.e. ammonium amide)?

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