Unit 5.5 - Graphite and Diamond

[@saberito91]

Can you please explain the P63/mmc Space group please

[@FrankHoffmann1000]

Hi, well, I can try it - apart from the following explanation I would recommend to watch also the units 4.5 - 4.7 and 5.1, in which space groups in general are explained. P6(3)/mmc (a) This space group belongs to the hexagonal crystal system; therefore we immediately know something about the metric of the lattice: a = b (c is usually different), and alpha = beta = 90 degrees, and gamma = 120 degrees. (b) "P" means that we have a primtive lattice (_lattice_ points only at the corner of the unit cell) (c) Then symmetry elements in three directions are specified. In the first viewing direction (=c-direction) there is a "6(3)" screw axis (rotation by 60 degrees, then translation of 3/6 (=1/2) in the positive c-direction. There is also a mirror plane ("m") perpendicular to the c-direction, i.e. in the (a,b)-plane. Perpendicular to the second viewing direction (along the a-direction) there is another mirror plane, and perpendicular to the third viewing direction there is, finally, a glide plane "c" (this means mirroring at a plane perpendicular to the [210]-direction and then translation of one-half of the unit cell along the c-direction). best Frank

[@saberito91]

Well thank you alot Sir, yes i figured it out last night, Primitive lattice '' 6 fold screw axis rotation by 360/6 and a translation by 3/6 of the unit cell'' parallel to c, mirror plane perpendicular to c, mirror plane m perpendicular to a, and a glide plane c perpendicular to [210], that's what i understood from your videos, it's been really helpfull, am working on understanding the MAX phases structure, well i've been able to see all of the mirror plans and also the glide plan c in the Max phases, ''Vesta nd PCOD were helpfull' nd i've been left with just one problem, it's the screw axis and they're translation of 1/2, parallel to c direction, i used ''space group vizualiser software'', Solidworks, vesta, the rotation by 60° is clear cause it's hexagonal, but the translation, but the 1/2 translation i couldn't see it, cause when the atoms are rotating on a axis, they're on the same (0,0,C) plane, so i think i'll search for a more understanding of the screw axes, well thank you alot sir, cause now, i am sure that i understood wright, if i can ask you something Sir, please is there any software that allows me to draw the complete lattice structure, or could we by using vesta in hexagonal structure see all the hexagon, not only the primitive cell, nd if there is an option for seeing the lattice cristallin structure, or joining two 3 primitive cells together? Best Regards Saber

[@saberito91]

Hello, Never mind sir, i think i understood the screw axes 63, that means 3 atoms on a same (0,0,C) rotating by 60° in the c direction by a translation on 1/2, i can finally see it in the max phases, :D thank you alot for your videos sir, i could never understand the space groups without theses awsome explanations, thank you thank you

[@FrankHoffmann1000]

Dear Saber, indeed VESTA is able to show more than one unit cell, choose the "Boundary..." button in the Style tab for this option. If you then look along the c-direction you should see a hexagonal pattern. VESTA is also able to generate a so called supercell, see for instance: kzbin.info/www/bejne/oGrOqZSlpdBmgrM Concerning the impact (or non-impact) of a symmetry element: if an atom lies on a symmetry element then the impact is sometimes not visible, at least for all symmetry elements with no translational component. But I do not know, if this is the case in your structures at hand (I am not familiar with MAX phases). all the best! Frank

[@saberito91]

Thank you alot sir, it was indeed really helpful!