17 ABAB stacking: Hexagonal Close-Packed (HCP) structure

[@pranav9339]

Apart from brilliant teaching, your beard and hair looks cool, prof ;)

[@shuunnya.shubham]

Beautiful explanation. Thank you, Professor.

[@robovj]

Best explanation of HCP! Thank you sir. Your lectures are very good and give clear understanding of the concepts.

[@allroundcompilations2326]

Hello Sir. We've defined lattice as the arrangement of points in space, where particles can be placed. So, can a particle (atom) be placed other than at the lattice point? Refer 13:30, where we've said that the atom inside the unit cell doesn't form a lattice.

[@introductiontomaterialsscience]

Yes, whenever there is more than one atom in the motif all of them cannot be located at the lattice point.

[@srinivasan3463]

In HCP crystal structure, when I looking at the diagram, it looks like lattice points at the corners and one is at the centre. It looks alike body centred. But there is no BCC IN HCP crystal??

[@rajeshprasad101]

But the one in the centre (atom in B layer) is not at a lattice point. Only the centres of atoms in A layer form the lattice. This is because the surroundings of A and B are different. Thus the lattice is simple hexagonal (or hexagonal P) for HCP crystal. Also note that for any body-centred lattice the centring point should be at 1/2 1/2 1/2. Here the B atoms is at 2/3 1/3 1/2 which is not really the centre if the unit cell. A related question is then what will happen if we do put the B layer atom at 1/2 1/2 1/2 and not at 2/3 1/3 1/2. Well, then it does form a lattice, but it is no more hexagonal. I leave this as an interesting exercise for the readers.

[@vedprakashsharma2388]

@@rajeshprasad101 sir if we put B 1/2.1/2.1/2 then the sequence became AAA.. Is it sir?

[@nimaipatro2960]

@@vedprakashsharma2388 no.. .. putting third layer such that it forms body centered will leads you to lesser packing efficiency....

[@jaswanthkumar8157]

Superb lecture very pleasant and understandable

[@vijayburugupalli5401]

By symmetry a simple hexagonal unit cell must contain a six fold symmetry. How does it (13.37) satisfy that?? Plz correct me if I'm wrong!!

[@rajeshprasad101]

Simple hexagonal crystal or simple hexagonal lattice has six-fold symmetry. But the six-fold axis is not visible in a single primitive unit cell. But when the unit cells are repeated to create the lattice or the crystal then the six-fold axes can be visualized.

[@luzhang1191]

According to the video at 1'58''. May I ask for sequence of A, B and C why there is no arrow from B to C (e.g. ACBC)? I thought the shape for ABCB should be same with ACBC, but why there is no arrow?

[@introductiontomaterialsscience]

You are right. there should be an arrow there as well. I just missed it,. Thanks for pointing out.

[@adityapatil2790]

@@introductiontomaterialsscience Sir then why not given explanation for ABCB/ACBC packing? As these are not giving AA, BB, CC combinations.

[@abinr8110]

clearly understanded............ thank you sir

[@jshkumar2]

understood not understanded

[@OxygenOS]

@@jshkumar2 lol

[@pranav9339]

Prof, as per geometry are 8 lattice points but effectively, only 1 atom (motif), lattice point is a geometrical concept, then how can there be only 1 lattice point, there must be 8 lattice points. Please correct my approach.

[@veenagupta3802]

Great explanation

[@ShuvamNayak]

Sir, I could not understand why you said, there is only 1 lattice point in HCP, there is 8 lattice point for HCP, isn't it?

[@introductiontomaterialsscience]

But the 8 lattice points are at the corners of the unit cell. This effectively gives one lattice point per unit cell.

[@harisankar614]

@@introductiontomaterialsscience sir my doubt is a lattice point , as u explained is just a point so how can we divide that single point and and contribute the part of a point to that unit cell ... is it possible to treat a lattice like an atom ?

[@rajeshprasad101]

@@harisankar614 You are right. We cannot really divide a point. But we can divide it in imagination for effective counting. Since 8 unit cells meet at a corner and if you count the lattice point at corner as 1 then for each cell you will get one lattice point at that corner. So that lattice point will get counted 8 times. Thus for effective counting it is better to imagine that each unit cell gets only 1/8 of the corner lattice point. So in total counting you will get 1/8X8=1 lattice point at that corner which is the correct number. I hope this clarifies.

[@buatakun191]

@@rajeshprasad101 Sir, i'm trying to understand your point, so we can imagine that if we resize the atoms in the corner to bigger size then we can look that there is 1/8 atom at every corner? One more Sir, so if there is 1/8 atom in the corner, we have to said that only 1/8 lattice point which effectively occupied the1/8 atom?

[@manishchugh9235]

Sir can I get idea about t v in hcp

[@introductiontomaterialsscience]

kzbin.info/www/bejne/gIPSlpewbJmIm7M

[@crackit5747]

It's going beyond my head.. can't understand even a single topic from material Engg.😢...

[@introductiontomaterialsscience]

Don't loose heart. Keep at it and you will ultimately succeed. Don't hesitate to ask any specific difficulty.

[@crackit5747]

@@introductiontomaterialsscience thanks a lottt sir..now I'll do my best, I'll again watch videos 🙏

[@209akashkumar4]

Aunty abb kaisa chal rha materials engg??😂😂😂